Vey puzzling overheating issue, not the usual suspects!

My 87 Wagoneer, 4.0, AW4, 4x4, (had it for 4 years, and 40,000 miles) is developing a fever!

It had major overheating problems when I bought it 4 years. The major culprit then was a partially blocked radiator. It had large cold spots and some hot spots. Replaced it with an el-cheepo $98 aluminum 1 row (1-1/2" row I think) plastic tank radiator that has worked great. I also replaced every single sensor on this 264,000 mile beast since I bought it, as well as a new fan clutch (4 years ago, and again last week), new water pump last week, new thermostat last week, new bottle in last 9 months, new dizzy a few years ago, new harmonic balance 2 weeks ago, new hoses, some last week, some last summer, new thermostat e-fan switch, and temp gauge sensor, new EGR 3 years ago, new O2 sensor 2 years ago, new five-o injectors 2 years ago, new FP regulator 3 years ago, new cat and muffler and exhaust pipe last year, new wires and plugs in last 20,000 miles, new MAP and new MAT (IAT) sensors 2 years ago. The old CTS was tested and was OK last summer. Only thing that is old is the driver and the XJ body, LOL.

No coolant in oil, no oil in coolant, tranny fluid is nice red color. Exhaust is very HOT, but clean and dry. No loss of coolant that I can find in 4 years, 40,000 miles, and no losses currently.

My daughter has an 89 xj that I did a head job on last year. It ran hotter than mine right after the head job, but runs about 20 F cooler now than then (according the dash gauge, so not sure that is right). Mine is running about 35 F hotter than it use to based on IR under the hood readings. Now mine runs about 20 F hotter than hers.

Last week I installed a new fan clutch (no change), new water pump (no change) and new lower rad hose, and a 160 F thermostat like I ran the first 3 years I had the 87 (used 180 F passed 12 months), but it made no difference in the final equilibrium operating temperature or the peak temp after a highway run followed by a stop to idle (to simulate heavy traffic, lights etc.).

I hot wired the electric fan, as the T-switch in the radiator has drifted from about a 185 F cut in to about 195 F cut in, at the radiator exit. That helped some, but it is still running 20 F hotter than my daughters, who also has the electric fan hot wired (on all the time).

My O2 sensor is reading slightly lean at idle (according to the Renix MPI FSM which says over 2.45 volts is lean) or about 3 volts at idle. Idle speed, and IAC is normal (maybe I should re-phrase that, it is working properly, LOL). It drops to about 2.7 volts average at 2000 rpm, versus book spec of 2.45 V, but those numbers are lower than they were last summer when it was around 3 to 3.5 V average (it was 2.45 V, dead on when new 2 years ago).

I tried disconnecting the O2 sensor once the engine was good and hot, and while it did cool off about 10 F in a bout 10 minutes of idling, it was still running 20 F hotter than the last 3 summers. I may try it again now that I have the e-fan hot wired. Ambient here has been about 85-95 F.

My only vacuum leak is during braking (vacuum booster replacement is on my to do list).

The cooling system is holding pressure, in fact the hoses are getting rock hard. Closed system coolant bottle, coolant level is very stable, no changes in last 10 hrs of testing.

I added the two bleed holes to the new 160 F thermostat as per 5-90's specs, and I have bleed air from the dash gauge sensor twice. I added a T fitting to the water pump feed to bottle/heater core hose to bleed air during filling (which helped). Engine has run a good 6 hours, on /off cycles about 20 times now since replacing the water pump and coolant refill. Running 50/50 DI water to antifreeze - coolant.

I have run extensive IR thermal temperature measurements on the 87 and 89, and find little difference except a generally higher, 20 F higher, Temp at the thermostat housing, and the return flow to the engine from the radiator return side with all other conditions being equal. Temps around the head at the intake / injectors look about 10 to 20 F higher in various spots in general, but the temps vary a lot in those areas in small changes of distance ( Exhaust is very close to various spots like intake and injectors) and my IR T gauge samples an area, not a small point location temp.

Intake at the EGR is cool, running about 145 F.

Muffler shop just tested my Cat back pressure and said the exhaust is OK, and not causing the problem, But I noticed today the Cat I pulled off the 92 jeep last week (looks like an OEM style) is physically about 4 times bigger than my new, 1 year old, # 91005 universal Magnaflow brand Cat. So I still have questions there, but for now I do know that my exhaust, while it may be a little restricted, is about the same as prior years, as I have monitored it. I have noticed that exhaust seems hotter than before!

Lastly, 4 weeks ago, the old (4 year) lower radiator hose came off the lower radiator nipple (blew off) and dumped all my coolant while on the freeway at 50 mph. This was caused in part by not re-tightening the 4 year old hose clamp on a plastic nipple that has nearly no ridge at the end to help hold the hose/clamp in place. All the coolant was gone by the time I got off the freeway and parked and killed the engine. I never saw any coolant loss, no steam, vapor. Only reason I pulled off and stopped was the Termo-dash gauge was reading 220 F, and I started to get off the freeway. It read 260 F by the time I killed the power, and cut off the engine. I waited 2 hours before refilling the jeep to let it all cool down. It ran fine with AC on, on the 30 miles drive home, just about 20 F hotter than normal according to the dash gauge that day. I topped off the coolant bottle the next morning, and it ran normal the next few days. Then one day I took my last 60 mile round trip with no problem, except for the harmonic balancer clicking enough to remind me to park it and change the HB, which I did 1 week ago. It has been running hotter again since I replaced the HB.

I have recently noticed that my dash gauge is not always reading the same as the IR T gauges, and it seems that it has always been reading lower than the true temp (20 F lower), based on sampling the head temp near the T sensor in the rear of the head, and it reads higher for a while after bleeding air off at the T-gauge sensor. But there is also about a 20 F rise from the Temp at the T-gauge sensor block area to the thermostat housing area (probably due a temp rise as the coolant flows through the head). There is also about a 20 F rise from the radiator exit to the rear top of the block near the T-gauge sensor location.

My daughters jeep after a long hard drive, idling in park, E-fan on (hot wired) is holding about 155 to 160 F at the radiator outlet (she has the same cheepo radiator I do, but hers is 4 years newer, only 6 months old) and about 185 to 190 F at the thermostat housing. She has a 180 F thermostat, mine is 160 F.

Mine, under the same exact conditions is running about 195 to 210 F at the thermostat housing and about 170 to 185 F at the radiator exit. I am getting an average 25 F drop across my radiator, and my daughter is getting about 25 to 30 F drop across hers. Both tests were with AC Off, E-fans on (hot wired). So while she is getting a slightly better delta T across her new radiator ( 5 F at most!), it does not explain the 20 F higher temps in my engine.

My engine has no known running problems other that typical old 4.0 valve train noise that it has had for 4 years and 40,000 miles. It passed a severe emissions test here about 8 months ago, with flying colors.

My last tank full of gas gave me the highest mileage I have ever gotten with this jeep/engine, so it had to be running leaner.

So now, what say you oh great gurus of the XJ overheating world?

Any way you can use an adjustable map and bump the voltage up a bit to see if you can get the o2 sensor back down to the 2.45V range? I know that on my obd2, the pcm would then pull the fuel back out, but how bout on a renix?

gradon said:

Any way you can use an adjustable map and bump the voltage up a bit to see if you can get the o2 sensor back down to the 2.45V range? I know that on my obd2, the pcm would then pull the fuel back out, but how bout on a renix?

Click to expand...

Even if I could, I tried just disconnecting the O2 sensor, which throws it into open loop, rich mode, and while the temp gradually dropped about 10 F at idle over a 10 minute span, it did not really solve the 20 to 30 F elevated operating T problem. Before, with no O2 sensor and a 160 F thermostat it would have run at about 165 to 170 F at the T housing and that was with no eFan running.

I suspect there is currently a slight wiring voltage loss (resistance) between my ECU and the O2 sensor (C101 bulkhead perhaps), but if it was the real problem it would have run real cool when I discoed the O2 sensor in a test earlier this week.

But thanks for the suggestion.

It sounds to me like it is running really lean once it comes out of cold loop. How do the plugs look ? It could have to do with partially blocked injectors that the ECU can't compensate for which means it is probably also running lean when it's in cold loop. Other option might be to try a colder plug for a while but I'd lean towards the injectors myself. The only real way to tell is to pull them and put them in a fixture and check the pattern they are throwing. No engine analyzer is going to be able to do that.

When the lower hose went, it probably got coolant all over and into everything in engine compartment. Could some of the sensors/injectors/connectors/etc. be semi-shorted/poor connecting/ full of coolant ? ? ?
Throttle body probably got a snoot full thru the air intake, sensors there, too!

Good Luck,
O

Silly question - when you were playing with the IR, did you happen to draw thermal maps of both engine compartments for comparison? This sounds like an oddy, and that information could be useful for the rest of the class...

What effect would coolant have on the O2s and Cat Conv.??? (comming thru the engine.)

O

orange said:

When the lower hose went, it probably got coolant all over and into everything in engine compartment. Could some of the sensors/injectors/connectors/etc. be semi-shorted/poor connecting/ full of coolant ? ? ?
Throttle body probably got a snoot full thru the air intake, sensors there, too!

Good Luck,
O

Click to expand...

Good question, Well it was already running about 20 to 30 F hotter earlier the day it later blew the lower hose off, then it was normal the next few days, then back to running hot again, so I kinda ruled that sort of thing out. The coolant came out at the lower radiator nipple, and I saw no signs of coolant above that area immediate area. I had not considered the possibility of it hitting the 2 sensor, which does not like silicone or silicates (silcates are in the coolant). But once again the O2 sensor and ECU seem to working, just running ever so slightly lean based on measurements, and it overheated the first time before any coolant escaped thus kinda rulling out that possiblity, but I will keep it in mind, in fact I may go wash off the lower drivers side area where the CTS and O2 sensor are, with DI water and solvent.

No coolant got into the air intake that I know of, but I will check the air filter right now to see if there is any slimy ethylene glycol residue.

5-90 said:

Silly question - when you were playing with the IR, did you happen to draw thermal maps of both engine compartments for comparison? This sounds like an oddy, and that information could be useful for the rest of the class...

Click to expand...

I thought about that, but No. I did check it many times before on both engines in about 20 spots, and I saw no significant changes, except that mine is uniformly about 20 F hotter at water pump inlet, T-stat exit, and at radiator entry and exit, and If I run the AC it is about 30 F hotter, an if I push it on the highway for a while with AC then stop in heavy traffic when it is 90 to 98 F outside it peaks up to about 230 F at the T-stat exit.

I did note that the #3 and #4 injectors seem to get about 20 F hotter than #1 and #6, due to the exhaust and intake pipe, and heat shield locations on both jeeps. Here EGR was a little hotter than mine, about 15 F hotter.

orange said:

What effect would coolant have on the O2s and Cat Conv.??? (comming thru the engine.)

O

Click to expand...

Silicates in the coolant would leave a light coating on the catalyst bed, possibly "poisoning" it.

Whether they'd burn off in time would depend on precisely what silicates they are, and whether they'd actually poison the bed or not would also depend on what silicates they are, and whether they can be split into things that would have an affinity for palladium, platinum, and/or rhodium.

Current ambient (during todays tests) 84 F.

CTS and MAT decoupled ohms were dead on to spec at 100 F (about 1380 ohms), and CTS was dead on at 170 F (During early warm up about 384 ohms) and MAT was good at 200 F (engine off, saturated, 250 ohms).

Cleaned the CTS wires and connector, and the O2 sensor with brake cleaner (chlorinated version).

With the AC off, I got to 170 F at the thermostat housing, and 140 F at radiator return after about 5 to 10 minutes of idling. Then peaked at about 180 to 185 F at T-stat and 150 to 155 F at radiator outlet. Turned on AC to get it hotter faster. Got up to 200 to 205 at T stat housing, and 170 to 175 F at radiator return. So I am getting close to a 30 F delta T across the radiator, maybe 3 degrees less that my daughters new radiator, at idle, in park.

I tried bleeding air from the rear block at the T-sensor, but got no air that I could see, just coolant. One thing is for sure, during warm up the T-sensor gauge combo reads a lot cooler than my IR gauge reads on the head near the coolant sensor, so the coolant itself from the radiator must still be a good 30 to 40 F cooler at the T sensor before it makes the final trip through the head to the T-stat housing, the upper radiator hose pressure (hand squeeze sensor) says the dash gauge may not be too far off.

All the tests were done after I inspected and cleaning the spark plugs (as needed).

Plugs 4,5 and 6 looked REAL good, almost new, just a trace of white powder on the ground electrode and insulator. 1,2 and 3 had some thicker white residue on the insulator and harder (not soft) white residue on the ground electrode, and a trace of light black carbon on the ground body (below the threads). I did run some injector cleaner last week, so it may be residue from that, but some of it was a little thicker and older on plugs 1,2 & 3. By thicker I mean 5 to 15 thousands thick, 20 at most on the outer, back side of the electrode, 5 thou on the tip insulator. # 2 had some, about 20 thosands thick in the curved inner ground electrode area. These are Bosch Platinum single tip spark plugs I have been using for about 20,000 miles (40,000 at most, as I think I changed them 2 years ago in a test with new ones). These all ohmed out at greater than 15 megohms, so they are not leaking voltage to ground.

All the residue came off with a SS wire brush.

I compared the exhaust velocity on my daughters 89 to my 87 today, and they are exactly the same at idle, so it does not seem to be a backed up exhaust.

5-90 said:

Silicates in the coolant would leave a light coating on the catalyst bed, possibly "poisoning" it.

Whether they'd burn off in time would depend on precisely what silicates they are, and whether they'd actually poison the bed or not would also depend on what silicates they are, and whether they can be split into things that would have an affinity for palladium, platinum, and/or rhodium.

Click to expand...

The silicates (sodium metasilicate) in the old green coolant formulas can coat over the metal catalysts permanently given enough coolant, but that would not be causing my problem, and I am not loosing coolant, except for that one instantaneous dump 4 weeks ago.

Ecomike said:

Current ambient (during todays tests) 84 F.

CTS and MAT decoupled ohms were dead on to spec at 100 F (about 1380 ohms), and CTS was dead on at 170 F (During early warm up about 384 ohms) and MAT was good at 200 F (engine off, saturated, 250 ohms).

Cleaned the CTS wires and connector, and the O2 sensor with brake cleaner (chlorinated version).

With the AC off, I got to 170 F at the thermostat housing, and 140 F at radiator return after about 5 to 10 minutes of idling. Then peaked at about 180 to 185 F at T-stat and 150 to 155 F at radiator outlet. Turned on AC to get it hotter faster. Got up to 200 to 205 at T stat housing, and 170 to 175 F at radiator return. So I am getting close to a 30 F delta T across the radiator, maybe 3 degrees less that my daughters new radiator, at idle, in park.

I tried bleeding air from the rear block at the T-sensor, but got no air that I could see, just coolant. One thing is for sure, during warm up the T-sensor gauge combo reads a lot cooler than my IR gauge reads on the head near the coolant sensor, so the coolant itself from the radiator must still be a good 30 to 40 F cooler at the T sensor before it makes the final trip through the head to the T-stat housing, the upper radiator hose pressure (hand squeeze sensor) says the dash gauge may not be too far off.

All the tests were done after I inspected and cleaning the spark plugs (as needed).

Plugs 4,5 and 6 looked REAL good, almost new, just a trace of white powder on the ground electrode and insulator. 1,2 and 3 had some thicker white residue on the insulator and harder (not soft) white residue on the ground electrode, and a trace of light black carbon on the ground body (below the threads). I did run some injector cleaner last week, so it may be residue from that, but some of it was a little thicker and older on plugs 1,2 & 3. By thicker I mean 5 to 15 thousands thick, 20 at most on the outer, back side of the electrode, 5 thou on the tip insulator. # 2 had some, about 20 thosands thick in the curved inner ground electrode area. These are Bosch Platinum single tip spark plugs I have been using for about 20,000 miles (40,000 at most, as I think I changed them 2 years ago in a test with new ones). These all ohmed out at greater than 15 megohms, so they are not leaking voltage to ground.

All the residue came off with a SS wire brush.

I compared the exhaust velocity on my daughters 89 to my 87 today, and they are exactly the same at idle, so it does not seem to be a backed up exhaust.

Click to expand...

By the time you read the post above you may be wondering if I have an overheating problem.

Just keep in mind that at 100 F outdoors (we have gotten very close to that already this year!, Yikes!), my numbers will be about 15 F higher, then tack on the engine loaded, adding more heat, AC running at 100 F (versus 85 in todays evening tests), and the tranny adding a heat load to the radiator, and then a traffic jam at 5 pm, and I will headed for 230 F easily, or higher with a plastic bottle in the closed system that is showing signs of stress this month. Not to mention radiator nipples that have already let go of one radiator hose under high pressure due to a poor (smooth almost straight ) shape at the end.

And is now running considerably hotter than the 89 jeep with the same exact hardware, and about 20 F hotter than previously.

Test results:

Fuel pressure is 30-42 psi, 30 after a rapid accelleration, then decel bottoms at 30. At idle it is 42 With out vacuum and 33 with vacuum attached to the FPR. No fuel leaks at the FPR.

Intake manifold Vacuum is 17.5" at idle.

19" at 2500 rpm. 20" at 3000 rpm, 25" peak at rapid decel from 3000 rpm and 0" going from idle to WOT for 1/2 second.

All indications of normal engine. Actually not bad for 264,000 miles.

Has anyone hear heard of low refrigerant change (seemingly normal working AC) causing overheating in heavy traffic?

Ecomike said:

Test results:

Fuel pressure is 30-42 psi, 30 after a rapid accelleration, then decel bottoms at 30. At idle it is 42 With out vacuum and 33 with vacuum attached to the FPR. No fuel leaks at the FPR.

Intake manifold Vacuum is 17.5" at idle.

19" at 2500 rpm. 20" at 3000 rpm, 25" peak at rapid decel from 3000 rpm and 0" going from idle to WOT for 1/2 second.

All indications of normal engine. Actually not bad for 264,000 miles.

Has anyone hear heard of low refrigerant charge (seemingly normal working AC) causing overheating in heavy traffic?

Click to expand...

Typo corrected, "low refrigerant charge"

I changed the air filter this evening.

Also bought a new bottle cap, # 7035, by CST, made in Germany, it has a different internal structure than the China cap does. It was in stock at Autozone! $6.99, The plastic on it feels harder than the china cap does.

Planning to buy and a try a 2 row all metal (copper/brass) radiator to try next, and I will check the R-134a charge this weekend in the AC to see if it is low.

On another note, I rented a radiator and radiator cap tester, and nearly blew up my diesel jeep radiator before I discovered the pressure gauge was only reading 9 psi when it was already at 18 psi! Good thing I checked the radiator hose at 9 psi on the tester gauge and figured out it was fubared. I won't have many nice words for O'Reiley when I return it!

5-90 has about convinced me that is not the engine, not a cracked block or cracked head or head gasket. There is no unusual blow by in the crank either.

I've never heard of a low aircon charge causing overheating - but that doesn't mean anything.

I don't care for aluminum radiators - seems as though they collect scale and crud too quickly. I prefer copper.

I'll keep kicking this around in the back of my head, and see if anything else comes up...

Just a thought -
- Could it be the Transmission pumping extra heat into the radiator? IR readings might show where the difference with other Jeep is comming from. *The extra heat has to come from someplace*!
-Swap O2 (or other easy, & fast stuff)with other Jeep for quick testing?

Regards & Good Luck,
O

I like to troubleshoot from simple to hard. Check the cap on the football and make sure it isn't stuck closed. The levels in my football rise and fall depending on motor temp. Yours remaining stable may or may not be a good sign. I can actually watch the flow through the football with the lid off (and the heater off)
As I'm understanding things, you are thinking lean is possibly causing excess heat? Possible... lean at idle is troubling. Though if the O2 sensor were very far off you'd likely notice some sort of lean detonation at around 22-2400 RPM, during middle to low vacuum conditions. Have you tried a vacuum gage yet? Fuel starvation (be it fuel supply or O2 or timing) often makes the Renix buck in the mid range.
In my experience the 4.0 idles a bit rich normally.
Low air flow tends to overheat them at idle or low RPM's no matter how good your motor/cooling system is. My temps. tend to drop in minutes (10 to 20 degrees depending on the ambient), below the aux fan on temp. (my thermal switch typically closes some higher than yours, around 207 F).
The hoses shouldn't be that hard, especially the top pump to radiator hose. The water pump does tend to push better than pull, but the only time I've noticed the top hose really hard was from a partially plugged radiator or air in the system building excess heat/expansion.
A simple test to check your radiator heat exchange, is to lightly spray the radiator with water, temps fall quick. The water evaporating off of the radiator leeches heat quick. If your radiator is covered in coolant, it may be a factor in poor heat exchange.
The system is balanced through rather broad parameters. How fast the coolant flows through the radiator is one. Too slow and you may get good heat exchange but poor volume. Too fast and you may get good volume but not get sufficient heat exchange. Poor heat exchange is also form poor or low air flow.
The coolant flow is generally from bottom to top and from rear to front. The Hottest coolant should be at the thermostat housing.
The football and heater supply lines bypass the thermostat and are helpful for keeping a fresh (real motor temp.) coolant flow at the thermostat. It's possible to have cool coolant at the thermostat and hot coolant behind the cool coolant. If that makes any sense. The different temperatures don't mix well, though they will eventually exchange heat, it can be a slow process. The football/heater supply lines keep a fairly constant (true motor temp) flow of coolant by the thermostat. Though when the heater valve malfs, you generally notice at the temperature gage, it will take wild swings from cool to hot.
I probably haven't helped much, just throwing a slightly different outlook out there, so you don't get locked in a logic loop.
If your motor is running excessively lean, you can generally see it on the plugs. A hot reading is better than a cold reading. You can also look down the spark plug hole with a flashlight and see the top of your piston. You may get a better reading there. Too lean tends to burn a clean porous (to pitted) spot on the piston top.
Remember the piston exhaust gases are under a lot of pressure, the cooling system is generally below 16 PSI, you may not lose enough coolant to even notice, but still be getting exhaust gases into your cooling system. This can heat things up quick. Sniff in the football opening and see if you can detect any exhaust smell. I've tried the litmus exhaust gas testers for the coolant in the past with mixed results. A leak down test, with a leaky head gasket, almost always shows some sort of bubbles or foam in the coolant. Tiny exhaust leaks into the coolant can be hard to troubleshoot.
Lastly, another oddball thing I've run into, is the radiator hoses sometime separate. The inner liner gets really soft and collapses into the hose, the outside looks fine.
I put and elbow into the radiator draincock position and a short piece of hose poking out past the sheet metal. Plugged it with a threadless bolt (sawed off the threads) and a hose clamp. I can save most of my coolant and use it again if it isn't very old.
Sorry about the book, I'm just trying to be helpful and think of some oddball solutions you haven't already looked at.
Check your belt routing again just for the heck of it. I actually thought it was impossible to do it wrong, my son proved me wrong on that assumption. Like I said, I most always troubleshoot easy (basic) to hard, cheap to expensive.
Smear a little coolant on a piece of paper, test it with an ohm meter. Coolant is actually a fairly good conductor, much better than water. No telling what kinds of grief it may cause if it gets into the wrong connector.

Re: Very puzzling overheating issue, not the usual suspects!

In the past 4 years, it has always run cooler with the AC on than with it off. The reason being that the when the AC compressor clutch engages it also turns on the electric fan (back up to the primary mechanical fluid clutch drive fan). The electric fan is working, but when I turn on the AC now the cooling system is getting hotter, where as in the past it use to always run cooler with the AC on. In other words, the last four years it ran cooler with the AC on, than off, because the electric fan adding more cooling to the engine coolant system than the heat the AC added to the engine load and condenser to radiator load.

So far there is absolutely no sign of a head gasket leak.

I ran it at idle in the driveway today, in park for 60 minutes non stop, at 100 F ambient, with the electric fan bypassed to run all the time, and it held about 175 F leaving the radiator and 205 F leaving the thermostat housing. (those are todays results, at 90 F ambient, a little better with the second new clutch, as the first new clutch was working one minute and then not the next, I got lucky and caught it playing hooky earlier today, working one minute and not the next, brand new clutch!

But at 90 F ambient, driving 25 miles at 50 mph, with AC on max, it got to 225 F at the thermostat housing and 185 F at the radiator outlet (with the new clutch, which I pre tested on the stove with boiling water this time). The dash gauge read about 195 F, and the IR gauge read about 198 F near the T sensor. If I stopped to simulate 5 pm stop and go traffic with AC still on it would have gotten hotter and probably overheated, especially if it had been between 2 to 5 pm at 100 F instead of just 90 F.

I will be checking the AC pressures next.

Other than a possible AC problem, I am leaning towards upgrading the radiator to a 2 row, copper/brass rad. While I have gotten away with an el-cheapo radiator for 4 years, specifically a one row, 1.5" row, aluminum radiator with plastic tanks, I don't think I have pushed it this hard in 100 F weather , with a completely, properly working O2 sensor, ECU system, and a working AC system set up with R-134a I did the r-12 conversion late last year), all at the same time. I have tended to drive my diesel jeep in the summer the last 4 years, and the gasser in cooler weather. In fact I just completed the R-134a conversion in August last year I think.

orange said:

Just a thought -
- Could it be the Transmission pumping extra heat into the radiator? IR readings might show where the difference with other Jeep is comming from. *The extra heat has to come from someplace*!
-Swap O2 (or other easy, & fast stuff)with other Jeep for quick testing?

Regards & Good Luck,
O

Click to expand...

Thanks, but in this case my problems do show up with tranny in park.

8Mud,

What about the AC issue, question I have raised. I know you have a lot more AC experience than I do.

I did have some pinging a month or so ago, but it was Valero gas, stopped when I went back to Citgo gas. Also I ran some FI cleaner through it the last tank. No more pinging at all.

What do you mean by checking plugs hot versus cold? Why, what do you see different?

You mentioned a litmus test, I heard that once before, does the excess CO2 in exhaust turn the coolant acidic, carbonic acid?

How much does your coolant bottle (football) liquid level change from cold to hot?

Mine stays the same, cold to cold, morning to morning. Maybe changes a little hot to cold, 1/2" at most. and hard to view or use unless you are on level ground each time, but never enough to alarm me like a leaking cap does when it boils over.

I have good flow through the football. I have no heater valve, it was not used in 87.

Right now, turning my AC seems to be the trigger, but I have hot wired the e-fan to keep it cool with AC off.