running hot to overheating at idle

I have a 96 cherokee with 4.0L that I am having problems with it running hot (215-225) at high speeds (75-80mph) on the freeway and will over heat into the red line at idle in the drivethru or trail. Intown driving or slower freeway speeds are ok (temp will 190-200)I have never let it get into the red (shut it off when it reaches the last white line). I have replaced in the past 2 years (10,000miles) due to failure: robertshaw 180 stat, hesco highflow housing, new water pump from orielly (factory replacement), hoses, heater valve, belt, fan clutch (xj standard replacemant), fan shroud, temp sensor and sender, radiator gdi 3-row (4 years back). I have a 9 blade (no idea what year, half the jeep has 97 electrical parts on it) aux fan that will come on with a/c but without it waits till the temp is about 220. I run a tranny cooler in addition to the plumbing in the rad. Coolant is 50/50 with distilled water and i have tried redline additive with little results. I keep the jeep maintained better than a NASA project so there is little to nothing in need of replacing (even straightened all the fins on the condensor & rad and clean passageways). I can't find the sourse of the problem, if the part is new i assumed it is working but now I am not so sure.

My thoughts is this a issue with being able to cool off the fluid in the rad or a fluid flow issue since I get a lack of cooling at idle and high freeway speeds? I wonder if the aux fan motor or fan clutch weak? (how to check without replacing again?) Is the high flow water pumps able to produce additional cooling capacity since the rad is slightly larger and restricted areas such as the t-stat housing and t-stat have been improved? In my head I compare it to exhaust systems, larger pipes are better until they are no longer matched with the dispacement of the engine. I have looked at the Hesco and FlowKooler and am leaning towards the Hesco since is if a completely redesigned casting instead of a few add-on paddles but I can't find any commparible tests just one sided "oh i put on on and its great" or "they cost too much they're a waste of money"

if everything is new, you might want t look into a blown headgasket

What do the sparkplug look like?

bluejeepkid said:

if everything is new, you might want t look into a blown headgasket

Click to expand...

if the head gasket is "leaking" would that cause over heating... cause if so you answered my question that i didnt have to ask:flame: oh tand the fire is just because its cool...

Spark plugs look typical for what I have seen since I purchased it 70,000 miles ago... bright white ceramic and a little carbon coating on the metal casted case (each plug is like the next cylinder). I have in the past, on many set of plugs, had issues with the plug internatlly arcing from the center electrode (white ceramic part) to the outer case of the plug... that doesnot seem to be the case this time.

As far as a blow headgasket goes... I have not seem any fluid mixing in the motor oil or coolant nor blue smoke out the exhaust. I plan on getting another set of compression readings this weekend... last set 6 months ago were reasonable, still had problems then just new parts in the cooling system now.

YoungLifeXJ said:

if the head gasket is "leaking" would that cause over heating... cause if so you answered my question that i didnt have to ask:flame: oh tand the fire is just because its cool...

Click to expand...

YES, it can definitly cause overheating

The overheating at idle is definetely the fan clutch. Even new ones can be bad, or just not up to spec. Many of us have upgraded to the ZJ (Grand Cherokee, 4.0 clutch, which turns faster than the XJ OEM clutch. I like the Imperial brand (Hayden) ZJ clutch the best, at Advance Auto. It may solve both your problems, but should solve the hot idle for sure. Others have installed a manual toggle switch override for the E-fan so they don't have to wait for the computer to turn on the fan at 220 F. Plenty of write ups here and the mod forum on these.
IF these don't work look for exhaust leak blowing on the block.

Ran into a GM guy who does test work on designing cooling systems... told me to check the cap on the radiator. He said that for every pound of pressure dropped in the rad they call one point which is equal to 8 deg of cooling capacity. (yes there is a limit, he said for GM its max benificial pressure is 16 to 18 psi) my cap could only support a tested 7 psi. Bought a new cap last night that tested to 18 psi. I plan on testing once we hit 100 deg today.

Update*** Replaced fan clutch again... purchased both the ZJ severe duty and the heavy duty and the XJ (I could only find 1 model). The ZJ heavy duty would not allow the fan to bolt on and the severe duty hit the radiator (would have to grind off about 1/4" off the fins of the clutch to get it to not hit the rad). I installed the new XJ model and there has been NO change in temp behavior. Checked for exhaust leaks, found none.

Don't know what to tell you on the fan mounting problem. Try another brand? Did you have the blade backwards?

The last stock OEM XJ clutch I bought was worse than the new one I was replacing. The ZJ worked better than any new clutch I have ever had.

The high speed problem sounds like the tubes in the radiator are getting clogged. Come to think of it, clogged radiator tubes might show up at idle too.

I have noticed that the newer radiators, last 15 years or so, are supper thin, and as such can clog must faster than the ones I grew up with.

update: fan clutch made contact with radiator on last offroad trip. since I had to put in a new fan I converted to all electric fans... 16" 3000cfm (radiator probe controlled thermostat) on right in place of machanical fan and on the left the factory computer controlled electric fan. I put in a new all metal 3 row radiator and a highflow hesco water pump.

New setup warms up much fast and so far no temps over 220 (thats when 2nd computer controlled fan comes on) onroad, offroad however it will still over heat even with both fans running (override switch).

Did compression test for head gasket and I think these figures are within ok standards.
measurements in psi, first dry second with 2.0 ml of oil:
#1- 135, 140
#2- 145, 150
#3- 130, 140
#4- 135, 135
#5- 135, 150
#6- 130, 140

I am still experiancing low power on highway, and overheating on the trail... am I expecting too much from this rig??? What else is there to check???

Anything obstructing air flow to the radiator? Trans cooler, p/s cooler, a/c condenser, big bumper, winch?

If your fan is hitting your radiator, I'm guessing your motor mounts are shot, maybe even your tranny mount.

joe_peters: I have a tranny cooler and a/c condensor, both have been inplace for many years prior to and problems. fyi, I have cleaned and straightened out the fins on both. running a/c while sitting still in comparison to a/c off with fan override switch on, results in significantly hotter temp. however in both cases both will reach an overheated temp.

Begster: The fan hiting the radiator issue has been solved. Yes the motor mounts are new as of 6 months ago; the tranny mount could use replacement but it is still in decent shape.


Today I took apart the distributor and found alot of build up on the new cap and rotor (no offroad driving since I put it on about a month back) clean everything up and put back together. Road test proved better throttle response but since it is 30-40 degress cooler right now i cannot replicate the situation.

Well, the low speed I would have attributed to a weak fan clutch, the high speed would be obstructed air/coolant flow.

What is the condition of your lower radiator hose? For years the XJ lower hose had a spring in it to prevent collapsing, but that has been mostly done away with, even at the dealerships. You might consider a high quality lower hose.

Do you have any exhaust header leaks? An exhaust leak against the block could be adding to your temps.

How is your transmission? If it is generating too much heat that could be a contributing factor.

Any belt driven accessories failing? Power steering, alternator, etc.?

Can you put some space between the a/c condenser and tranny cooler?

And lastly, rent a block tester and check for combustion gasses in the coolant.

-What fuel MPG are you getting ?

-Try another thermostat ? -holes at 12 & 6 o'clock?

-after 'burping' is the radiator cap NOT being opened ?

Good Luck,
Orange

Anyone have experience restricting fluid flow? It allows it more time in the radiator to cool. I saw it on GoJeep's site:

http://go.jeep-xj.info/HowtoRadiatorRestrictor.htm

Might be worth a try if you're at wits end.

smcdonaldaz said:

Anyone have experience restricting fluid flow? It allows it more time in the radiator to cool. I saw it on GoJeep's site:

http://go.jeep-xj.info/HowtoRadiatorRestrictor.htm

Might be worth a try if you're at wits end.

Click to expand...

This is a controversial issue. I know racers have been doing this for years, and many claim success with it.

I think more flow is more likely to solve overheating problems. The orifice used for racing is to eliminate the possibility of a stuck thermostat, IMHO. They select just the right orifice to get the optimal operating temperature, and to help hold a stable operating temp and heat flow.

A few things to look at

Are you sure the gauge is accurate? '96 was a transition year, but the older models had a one-wire temperature sender for the gauge on the back of the head near the grounding strap (newer models consolidated the gauge with the sensor in the thermostat housing). If you have a dedicated gauge sender, you need to compare it against other readings, either with an IR gun on the thermostat housing or a scanner hooked up to the computer that reads the sensor in the thermostat housing.

If your fan clutch was contacting the radiator I'd suspect you have an oversized radiator, and probably have very fast coolant flow. Restricting the hose with a PVC insert will slow it down.

There are also the "traditional" problems that would cover high-temps at cruising speed--dead or dying water pump, clogged cat, etc.