Please help me!

ok, heres how it goes. ive got a 90 Cherokee 4.0 Laredo. AW4. It has a new radiator, water pump, thermostat (180). new upper and lower hoses, and new coolant overflow bottle. all the other hoses are fine. also, there are no coolant leaks. and the clutch fan is working and i wired the electric fan to a switch inside. i can start it up, let it run for maybe five minutes max with the electric fan going all the time. the temp gauge keeps climing past 210 degrees. the oil looks regular (not like its mixed with water) and there is no water coming out of the exhaust. the thing that puzzles me is that i can put my hand on the valve cover when it says it's past 210 degrees and it feels like its around 140 degrees max. keep in mind that the 90 Cherokee 4.0s dont have a temp sensor in the goose neck for the thermostat. with all this being said, what do you guys think is my problem with the Jeep? any help would be great and ease my mind a little. thanks in advance. :bawl:

isnt there a temp sensor on the back of the engine, close to the firewall? that would be the one i'd check....

Buy one of the mini hand held infrared temperature readers at Harbor Freight tools for like $10, then take temperature readings of the radiator inlet, outlet, thermo housing, etc to see what the real temperatures are. Then you will know if it is the gauge sensor that is off, or the engine that is overheating.

so the temp gauge is right. what could my problem be with the Jeep wanting to heat up way past 210 degrees in five finutes?

jk333 said:

so the temp gauge is right. what could my problem be with the Jeep wanting to heat up way past 210 degrees in five finutes?

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Possibilites:

The wrong thermostat, i.e. it is not allowing enough water flow to meet OEM standards, or a defective, though new, thermostat. Is it an OEM thermostat, which one, brand and part number did you use?

Air still trapped in the engine, and thus restricting flow. Burping trapped air out of 4.0s has been reported to be an ART here. Not burping them has been reported to cause overheating, and rapid boilover. I would read some threads on burping the air out, and try that first, it costs nothing but some time!

The O2 sensor, or the wiring from the ECU to the O2 sensor to the ECU ground could be partially defective (but not dead) giving bad data to the ECU, and thus causing the ECU to run the engine very lean (air/fuel ratio), which can overload brand new cooling system. You can read up on O2 sensor testing for the 90 Renix, at the end of a thread "The ReniX Files" that I started.

Exhaust pipe restrictions, like an internally damaged Cat converter, or partially blocked exhaust system can cause overheating, but is usually noticable as a lack of WOT power.

Any combination of the above.

Lastly, but very unlikely, is wrong water pump rotation direction, or loose impeller on the shaft, also unlikely since it is new, so put it at the bottom of the probabilyt list?

Hose spring missing in the lower radiator hose can cause problems, but not at idle in the driveway.

Thermostat is stuck, or not really filled up with coolant. Turtle tanks are notorious for leaving air in the system, you replaced it and drained a lot out, it will need to be burped a few times to really fill it.

A 180 stat is too low for the fuel injection and will run on "choke" trying to warm up the engine. A 195 stat is really required for max fuel economy.

You can change out the neck to a '92 up and wire in the temp control for the fans through it - works for me when it changed out to an open system.

Lower hose springs just keep the hose open when the pump is cavitating from a clogged up radiator that won't flow. Not your problem.

Carefully feel the upper hose while it's hot. The hose should also be hot. If not, then, like TiRod says, you may have a lot of air trapped (common with closed systems). Does your electric fan come on? Do you have AC? Does the fan come on when you turn on the AC?

thank you Ecomike for your help. when replacing the thermostat, i bought it from the Jeep dealer, so im assuming that that is the most reliable source. i did try to burp the cooling system, but didn't have very good luck. and since then the Jeep has been rolled around, and the water level didn't drop in the coolant overflow bottle, so im not sure that that's the problem, but it could be. the exhaust i don't think is the problem, i just had it in the shop for a new cat.and they checked out the whole system. however, i will check the O2 sensor and the ECU. you know the one thing i forgot about was that it might possibly be the head gasket. But, the main things ive heard about the head gasket going out is: water comes out of the exhaust and the oil looks like a milkshake. but my Jeep doesn't do anything like that. what do you think: head gasket? :shiver:

RE: Carefully feel the upper hose while it's hot. The hose should also be hot. If not, then, like TiRod says, you may have a lot of air trapped (common with closed systems). Does your electric fan come on? Do you have AC? Does the fan come on when you turn on the AC?


the upper hose doesn't get that hot.im not sure about the burping the system becaue i have tried filling the bottle shaking the rig and moving it around to make the water go down, leaving the coolant bottle cap off over night, but the coolant level doesn't go down. i run my electric fan all the time from start up to shut down (hard wired) i do have AC.

If you change out the thermostat, always drill a 1/8 inch steam hole in the new one.

Works for all engines.

Sounds like you have trapped steam or a bad temp sensor.

With the engine cold (at least cooled a bit), take the cap off the bottle. Try squeezing the upper hose like you were pumping it. You should see coolant squirting out the return line into the bottle.

My '88 is closed too and fully burping it can be tricky. Some people suggest parking on a steep downhill (or jack the back up as far as you can), and remove the temp sensor on the back of the head. If you tilt far enough, this will be the high spot and air will come out until it's full.

When I replaced my radiator, hoses and poly (turtle) bottle, I had no problems with burping it, I just ran it, cooled it, topped off the poly bottle itself while running and after cooling it, all with the cap off, a couple times and that was that. I never let it get hot enough to boil over with the cap off while purging the air. Is the poly bottle cap also new???? The plastic cap is a 16 lb pressure cap, and if it does not seal on the plastic bottle properly it will not hold pressure and thus will get too hot.

I run a 165 F thermostat on my 87, and the 90 model OEM does list an optional, OEM Jeep, specifically a 180 F thermostat. The 87 to 90 Renix seems to happy with a 180 F thermostat. The newer HO 91 and later models may need the 192-195 F thermostat.

I like the checking the upper radiator hose ideas! All it takes is a large air bubble right under the thermostat to hold up, or delay the coolant flow, and keep the thermostat closed.

" Lower hose springs just keep the hose open when the pump is cavitating from a clogged up radiator that won't flow."

I think it is actually peak flow at WOT, high rpm that colapses the hose, not a clogged radiator.

For those of you that have NOT read the entire thread (Before replying), he has a NEW radiator, water pump, hoses, Jeep Dealer OEM thermostat, and tutle bottle JUST installed, and a verified good working fan clutch. It is overheating at idle in just 4 minutes, in the driveway, in Park, AC off, Electric fan basically hot wired on all the time.

"when replacing the thermostat, i bought it from the Jeep dealer, so im assuming that that is the most reliable source. i did try to burp the cooling system, but didn't have very good luck. and since then the Jeep has been rolled around, and the water level didn't drop in the coolant overflow bottle, so im not sure that that's the problem, but it could be. the exhaust i don't think is the problem, i just had it in the shop for a new cat.and they checked out the whole system. however, i will check the O2 sensor and the ECU. you know the one thing i forgot about was that it might possibly be the head gasket. But, the main things ive heard about the head gasket going out is: water comes out of the exhaust and the oil looks like a milkshake. but my Jeep doesn't do anything like that. what do you think: head gasket? :shiver:"

Ok, the new thermostat could be bad. If you pull it, it can be tested in a hot water pan, along with your new IR thermo toy to test the water temperature!

You can test the lean fuel, partly defective O2 theory by simply disconecting the O2 sensor, which forces the Renix ECU to run the engine rich, and cold, unless one of the other sensors is giving bad data like the CTS, IAT or MAP sensor, which can under certain partial failure modes can also make it run lean, but it would eliminate the O2 sensor and circuit as a possible cause of it running lean. Just for test purposes (as it reduces gas mileage) I know from experience that you can disconnect the CTS (coolant temp sensor as well as the O2 sensor at the same time on Renix, and Renix will run it cooler and richer with out any other problems, other than poor mileage, so it makes an easy test procedure.

Now for that nasty head gasket question, head gasket leaks can take many forms. So yes, even though all your head gasket leak tests are negative so far, it is possible, but I don't think it is probable based on your current symptoms. Head gasket leak (exhaust leak into the coolant system) usually shows up as free combustion gas flow blowing fluid out of the open turtle bottle with the cap off, or a foam over with the cap off shortly after starting the engine.

It is possible to do a pressure a test on the coolant side of the system for a very small leak, but the turtle cap is somewaht unique on the 87-90 Renix, so finding a radiator pressure cap test rig may be very difficult, might be easier to rig up some heater hose and pipe fittings with some custom gadgets and pressure gage than to find a rig to fit the turtle bottle cap.

There is an inline hose adapter available that uses a standard 16 lb radiator cap you can buy (anybody got the link??) and install on the upper radiator hose that simplifies pressure testing the coolant system / head gasket.

Also, the heater core could be leaking, but I would still make sure the thermostat is not bad out of the box, and that the system is fully burped before moving on to the more exotic possibilities.

Thanks again EcoMike. i will take the thermostat out and test it in hot water and i will explore the O2 sensor and CTS routes as well.

When the thermostat is out for testing , fill the block and the radiator through the upper radiator hose, until coolant overflows from the block / thermostat housing. Then once the thermostat and housing is back on, fill the upper radiator hose while elevating it, and then quickly shove it on the thermo housing as fas as possible. It will reducing the amount of burping needed.:sunshine:

jk333 said:

Thanks again EcoMike. i will take the thermostat out and test it in hot water and i will explore the O2 sensor and CTS routes as well.

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So my neighbor works at the local Chrysler Jeep dealer. i was talking to him and he said he would help me in his spare time. we tried about everything. and finally determined it is a bad head gasket. so it looks like im gonna have to shell out some dough for that one. anyways, just thought i'd give u guys an update on what's going on. thanks to all of you who gave me advice on the cooling problem, especially Ecomike.

So do you know where the head gasket is leaking from and into???? And how bad the leak is?

Sometimes they can be sealed with a coolant chemical additive if they are in the right place and small enough. If so it might last long enough to buy you some time if you are strapped for cash. The block sealers only cost a about $10.

jk333 said:

So my neighbor works at the local Chrysler Jeep dealer. i was talking to him and he said he would help me in his spare time. we tried about everything. and finally determined it is a bad head gasket. so it looks like im gonna have to shell out some dough for that one. anyways, just thought i'd give u guys an update on what's going on. thanks to all of you who gave me advice on the cooling problem, especially Ecomike.

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Stupid question, is the thermostat installed correctly. You can put them in backwards way too easy even if you know what you are doing. Don't bother asking how I know.

old_man said:

Stupid question, is the thermostat installed correctly. You can put them in backwards way too easy even if you know what you are doing. Don't bother asking how I know.

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No bother at all, HOW DO YOU NOW? :doh:

And all this time I thought I was the only one that did dumb stuff like that. What's really irritating is when your consistant, and do it backwards twice in a row.:twak::roflmao: