Overheating at idle tried everything!

[3XJFamily]

I've got a new motor 95 4.0HO 700 miles on it so far, and it's running hot especially at idle or slow speeds. Yeah I know a new motor runs hotter but, this just seems too hot. Temperature eventually climbs to 215 on the highway but once I'm in traffic or wheeling around, it gets to about 225.

If I run the heater it will drop to 205 on the highway, and when I kick on the Aux fan by turning on the A/C, it will come down to about 215.

I'm running 31's / Auto/ 3.55 gears and the motor has Accel 21# injectors, and a Banks header, hi-flow cat and a dynomax muffler. Tanked the intake, and cleaned the TB before putting it all together.

Radiator = GDI 3 core (rodded out yesterday)
Clutch Fan = New as of yesterday
O2 sensor = new Mopar
Hoses = new Mopar
Thermostat = new Mopar
Aux fan = late model
Both temp sensors, IAC and MAP replaced last year
Radiator cap Last year
Water Pump Last Year

Running distilled water and antifreeze at 50%

I guess I'll try a new Radiator cap?

I guess next step is a high flow water pump but it seems this engine should cool with good OEM equipment.

Any ideas?

[TacticalFats]

My 97 (4.0/91k miles, all new cooling system except for the heater core)has always gotten warm when idling. It'll go to the line to the left of 210 when the fan kicks on and cools it back down to just over 210. Driving around it's usually right around (over if it's warm, just under if it's cool) 210. Flogging the motor has no effect on my truck's temp (in any weather), but idling it does.

Go figure.

[BCParker]

210 is normal.

if it's running at 225, I would be a little bit concerned, but that doesn't seem especially hot.

seems like you've checked/replaced just about everything.

how is the belt?

[jfiscus]

I was having the same issues with my 93 motor and figured out that the electric fan wasn't kicking in when it should have been. I put in a switch to turn it on manually and now it does fine driving around town in stop-n-go traffic & whiel 4-wheeling. (temp never gets above 205 with the fan on)

[martin]

I looked over your list, you do list radiator hoses. Did the lower radiator hose have the internal spring? The spring is there to prevent the hose from being suck shut, if that happens no coolant flows.

Okay another over looked source of overheating is a partially clogged Cat or a stopped up muffler. Have you noticed your MPG down?

Did you replace the exhaust system when you changed the engine? How many miles on that "high flow cat" and "dynomax muffler". If they are new with the engine you may have one or both of those components bad.

I had a buddy have a tile in his Buick cat tilt and cause a huge back pressure, he had it changed and solved his high temp problem.

I found my 88 XJ actually has more cooling capacity with a 2 row Modine over the 3 row GDI I had in it. I think rodding out radiators is a thing of the past since you can pick up a replacment from 100-200 bucks. I paid $116 + tax for a new modine at the distributor here in town for my 88 XJ.

After you have had verified the things I said I'd recomment with all the over heats to install a new MOPAR thermostat and Radiator cap. My radiator shop in St Louis told me one over heat to 225F is enought to damage a thermostat. Generally if it is damaged it opens late and closes late so you have wide swings on temp.

Hope that helps

[Li0nHart]

Your clutch fan is slipping badly..replace it...temp will go down

[n5xl]

Okay another over looked source of overheating is a partially clogged Cat or a stopped up muffler. Have you noticed your MPG down?

x10000


With the list of things you've changed, thats the next best place to check...I'd change it anyway along with the muffler. For whatever reason, my better halfs XJ is hard on cats...BOTH kinds..come to think of it, the grill is busted and there are a few feathers in the radiator. Maybe kitty was having lunch! :D

[churky89]

When was the last time the cooling system was backflushed...
A clogged heater core and crud build up in the water passages in the block will cause any vehicle to over heat
Wire a switch to the aux fan...

[3XJFamily]

210 is normal. Yeah "210 straight up". . . Then when it starts nudging past that on a 50 degree day, I have to consider what it will do in July at 108. . .

if it's running at 225, I would be a little bit concerned, but that doesn't seem especially hot. Boy it sure looks hot on the guage, sure concerned the Jeep mechanic with 20 yrs experience when he saw it creeping up, and with a new long block in there, I'm especially concerned.

how is the belt? No squeal, and no sign of glazing.

Your clutch fan is slipping badly..replace it...temp will go down Tried that yesterday = no change.

Did the lower radiator hose have the internal spring? Yup.

When was the last time the cooling system was backflushed...
A clogged heater core and crud build up in the water passages in the block will cause any vehicle to over heat Full backflush a year ago, Water passages in the block were clean (and dry) when I put the long block in a month ago. I've just replaced all the coolant a 2nd time = not much crud in there.

Okay another over looked source of overheating is a partially clogged Cat or a stopped up muffler. Have you noticed your MPG down? Did you replace the exhaust system when you changed the engine? How many miles on that "high flow cat" and "dynomax muffler". If they are new with the engine you may have one or both of those components bad. While I don't recall any sudden drop, mileage is bad on this rig (about 13.5 combined) but it is heavily armored, roof racked, winch equiped, 3" lift and still running 3.55 with the 31's. The cat and muffler are about a year old, maybe 10K on them. The old engine was suffering blow by bad - oil poured out of the intake when I removed it, and it was pretty crudded up in the combustion chamber too. . . hmmm. . .

Any easy way to test the cat / muffler?

I found my 88 XJ actually has more cooling capacity with a 2 row Modine over the 3 row GDI I had in it. I think rodding out radiators is a thing of the past since you can pick up a replacment from 100-200 bucks. I paid $116 + tax for a new modine at the distributor here in town for my 88 XJ. Yeah, I'd prefer a 2 row modine but I had an old GDI in the shed, and I got it rodded for $45 - more just to eliminate the obvious "replace the radiator !" solution.

After you have had verified the things I said I'd recomment with all the over heats to install a new MOPAR thermostat and Radiator cap. My radiator shop in St Louis told me one over heat to 225F is enought to damage a thermostat. Generally if it is damaged it opens late and closes late so you have wide swings on temp. Replacing the month old thermostat, and year old radiator cap were my next tasks - cheap and easy. OK, how to test the Cat and Muffler - Anyone?

[old_man]

I would take it to have a tail pipe reading done. It sounds like you are running too lean. This is common with headers on an HO. A spark plug reading will work but on newer engines it takes a skilled eye. A tail pipe sniff is the best. Surprisingly running too lean can hurt your mileage as well. If it is too lean, you might want to build/buy a MAP adjuster.

The other thing is that your gauge may be reading incorrectly. It is actually fairly common.

If it is not boiling over or losing coolant, I wouldn't worry short term.

[3XJFamily]

I would take it to have a tail pipe reading done. It sounds like you are running too lean. This is common with headers on an HO. A spark plug reading will work but on newer engines it takes a skilled eye. A tail pipe sniff is the best. Surprisingly running too lean can hurt your mileage as well. If it is too lean, you might want to build/buy a MAP adjuster.

The other thing is that your gauge may be reading incorrectly. It is actually fairly common.

If it is not boiling over or losing coolant, I wouldn't worry short term.

Since we've gone to emissions testing here, it probably shouldn't be too hard to get a sniff test done. It was diagnosed as running lean by a skilled eye, and we replaced the O2 sensor. I'd have "thought" the OEM MAP could manage manage to deliver enough fuel - expecially at idle - but, if you say it's common to run lean with headers, apparently not!

I figure the guage isn't 100% accurate but when it read a little past 210, we used a laser temp guage and read the thermostat housing at 213. On the highway it's on the high side of 210 when it's hot out, and the low side when I run the heater so I figure it's "close enough" to say that when it's climbing well past that at idle, something ain't quite right.

I had one boil over after turning it off and temp jumped up (to be expected), and also just replaced the overflow jug which I found a crack and slow leak in.

Trying not to worry short term but, got a lot invested so looking for a permanent fix - especially before it gets hot out.

[Johnny V]

I might have missed if it was asked....but did you purge the air out of the system?

My '89 had the same behavior as yours after I installed all new hoses, pump and thremostat. It overheated on warm days. Purged the air out using the temp sender hole and all is good now.

[jfiscus]

Air trapped in the block can cause these same types of symptoms in the closed system. I had assumed you upgraded your cooling at the same time as your engine when I posted my earlier post.

[CommandoXJ96]

i really doubt it would be possible; but i had it happen to me recently - check your Heater Control Valve.

[3XJFamily]

did you purge the air out of the system? It's an open system with an OEM thermostat - little weep hole at 12 o'clock, I figured it would purge any air after a few cycles. I put it nose down and checked via the temp sending unit this morning. Just coolant under pressure came out, no air . . .

check your Heater Control Valve. No leaks and heater works fine. I had disconnected the lines to the heater core, tracing down a drip, trimmed them up and reconnected. Lucky me the heater core was not bad, and the valve didn't break!

Update:
I made the run to work this morning, (72 outside) and the temp fluctuated 205 to 215 (normal but not steady) the whole way in and never heated up at stop lights - even dropped to 205 once. Seems like I used to see the temp guage drop in the mornings when the thermostat opened but, it just climbs straight to 210 . . Makes me suspicious of the thermostat.

I've got to run some errands at lunch so I'll see what it does and try and get a sniffer on the tail pipe for cheap. Tomorrow morn it's supposed to be 38, so at least in the short term, my problem may be undetectable.

[langer1]

It's a new motor they don't run hotter when new.
What happens is the heat is transferred faster with the nice clean passages.
As the crud builds up the temp gauge will not go from 205-215 it will level out around 210.

[3XJFamily]

It's a new motor they don't run hotter when new.
What happens is the heat is transferred faster with the nice clean passages. I'll buy that heat transfer is better with clean passages and any additional heat from friction during the break-in period is either insignificant or a myth.

As the crud builds up the temp gauge will not go from 205-215 it will level out around 210. but the sensor is a yr old (see my original post).

My complaint in the original post was that the "Temperature eventually climbs to 215 on the highway but once I'm in traffic or wheeling around, it gets to about 225". . .

So. . . this morning I see 205 in traffic (instead of 225), and a fluctuating 205-215 on the hwy (instead of a steady climb to 215).

[langer1]

I'll buy that heat transfer is better with clean passages and any additional heat from friction during the break-in period is either insignificant or a myth.

but the sensor is a yr old (see my original post).

My complaint in the original post was that the "Temperature eventually climbs to 215 on the highway but once I'm in traffic or wheeling around, it gets to about 225". . .

So. . . this morning I see 205 in traffic (instead of 225), and a fluctuating 205-215 on the hwy (instead of a steady climb to 215).
Well great it's still clean.
Just one thought, temp senders are fragle, it's very easy to mess them up if you over tighten them.

[black93xj]

Did you get all of the air out of the system? Sometimes that causes it to rise in temps. Try some water condioner. And just an idea could your ac condencer be packed full of corosion and not allowing air through the radiator?
Some times they look ok but if you hold them flat and shake you get piles of aluminum dust.

[cmeuzelaar]

...when I kick on the Aux fan by turning on the A/C, it will come down to about 215.

I didn't see anything that stated that you checked the coolant temp switch for the aux fan in your list. I'm not certain if newer jeeps have those (I have an '89), but if it failed, it would explain some of the cooling problems you're seeing.

[3XJFamily]

Yup, checked the temp sender at the back of the head just this morning, no air. A/C condenser was pulled and cleaned when the radiator was out. Switch for the Aux fan was replaced a year ago, and I watched it switch on once when I had the boil-over.

Took it out at lunch 205 on the highway and pretty much 210 at idle. I hadn't tightened the temp sender enough so had a leak there- tightened it up, topped off the radiator - and no more problem.

I'm really leaning toward a bad/sticky OEM thermostat (right out of the box) being the problem - if it happens again, that's next on the list. . .

[Johnny V]

Took it out at lunch 205 on the highway and pretty much 210 at idle. I hadn't tightened the temp sender enough so had a leak there- tightened it up, topped off the radiator - and no more problem.


You probably just fixed the problem and didn't even know it...by purging the system while driving!

[3XJFamily]

You probably just fixed the problem and didn't even know it...by purging the system while driving!

That's what I'm thinking too. Running it hard all weekend and it never had a problem, around 210 all the time now.

[Panama XJ]

95 HO engine use 21 lbs/hr @ 39 (21lbs/h@ 39) psi but Accel rate 21 lbs/hr @ 44.1 psi so you are getting about 19 lbs/hr @ 39 psi.

[3XJFamily]

95 HO engine use 21 lbs/hr @ 39 psi but Accel rate 21 lbs/hr @ 44.1 psi so you are getting about 19 lbs/hr @ 39 psi.

&^@#!! I hadn't thought of the slight difference in psi rating as having that big of an effect when I picked those out but, I just did the calculations and you are right.

I am still planning on getting the emissions tested. But, wouldn't this be a lean condition at Wide Open Throttle as opposed to idle?

Dealer prices on injectors were ridiculous when I checked (but I may have a line on a discount). If not (credit Dr Dyno), these may be my next choice:
Accel 24.4lb/hr @ 44.1psi (ACC-150124) = 21.6 @ 39 psi
Chevy LT1 24.0lb/hr @ 43.5psi (Part no. 17124248) = 21.5 @ 39 psi

Since my cooling problem has gone away, I'm gonna start a new thread in Mod Tech regarding the injector issue and let this one die.