So I bought my jeep used (1997 4.0). I figured I would replace all the fluids since it would be cheap insurance and have a baseline when the maintenance was done. The records were pretty bad. So I replace the coolant and burp the system, the temp would go up. Tried again, same thing. I have replace the t-stat and the housing. Same thing. Replaced the water pump, same thing. Replace all the hoses, same thing. Everything has been flushed completely (since I kept replacing parts). so that is good. the rad has been replaced by the last owner all metal not the stock metal and plastic.

The problem is that driving around town runs great. Light highway (ie only on there for 10 or so miles) great. If I go for a longer drive on the highway the temp will start to creep up to the red after 30 minutes or so. I can’t figure it out. The only thing left, or well two things but one I don’t want to do. The first the head or HG has a very small crack. But I am not losing coolant and the oil is not milky. This started after I change the old (really nasty) coolant. Maybe the bad coolant made the engine run better. (I don’t think that is the case). I REALLY hope its not. Or second I just give up and bring it to the dealer. I do not want to give up and drive it. So JF help!?!? Please.

And I have been searching.

 

So I bought my jeep used (1997 4.0).... the rad has been replaced by the last owner all metal not the stock metal and plastic.... If I go for a longer drive on the highway the temp will start to creep up to the red after 30 minutes or so.

I heard the all metal or all aluminum radiators have issues like these. What did you replace the radiator with? Stock?? Do you have any other issues like CEL's, running rough, high idle, and is there anything in your AC fins?

PS anything in front of your radiator like a winch, lights ro grill incerts?

 

If, you have AC, check for debris between the radiator and condenser comes to mind.

 

fan clutch

 

The fan clutch seems to be working correctly. I cannot spin the fan more than a quart turn if that when cold. I think that is how you check. Thanks for the idea.

 

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. This is normal routine maintenance that should be done on all vehicles. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat. The most important maintenance item is to flush and refill the coolant periodically. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat. Coolant should be replaced every 36,000 miles or every three years.

-Use a flushing/cleaning solution and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With a neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the 4.0 Liter thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap. An old worn out cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
- Check for any coolant leaks, hoses, fiitings, frost plugs, etc. If the cooling system is not pressurized due to a leak, your boiling point is significantly reduced.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that "looks" OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay (if your Jeep had one). Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here -

www.offroaders.com/tech/engine-overheating.htm

www.familycar.com/classroom/coolingsystem.htm

 

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. This is normal routine maintenance that should be done on all vehicles. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat. The most important maintenance item is to flush and refill the coolant periodically. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat. Coolant should be replaced every 36,000 miles or every three years.

Thanks for the info.

 

Have you changed the radiator cap and checked to see if the fan clutch is functioning properly?

 

Yes replaced the radiator cap and the fan clutch works. thanks for your ideas.

 

Mine does the same. It is the original radiator with 175,000 miles. I know my problem is a clogged radiator. When I drained it (during the flushing process) you could see the particles that were clogged in the radiator rows.
It runs perfect around town, but at highway speeds she slowly gets warmer and warmer till it overheats. The new radiator should be here soon. I follow up with you!

 

I am going to order a new one today or tomorrow. Yes please let me know what you find out! that would help a lot.

Which/what radiator did you buy? OE from Mopar/Jeep (plastic top)? or aftermarket?

 

The only thing it might be is a clogged rad, there was rust particals when I did a flush a while back but figured it still flowed water out so it would be fine. I am guessing not? maybe i will just purchase an OE radiator and see if that fixes the issue. The A/C condensor has some little stone chips in between the fins that are don't some out of the ordinally.

The stuff I replaced was swapped out with new OE Jeep parts.

 

did a little research and many people say "1 row cools better than 2" but that is based off the thickness of the cooling fins not just the numbes of rows inside the radiator. Alot of others say go with the 2 row oe replacements. Sooo... I was torn. I am going with the two row replacement. Ive read a lot that says aluminium vs copper core, and plastic vs aluminium tank. Youll have to make your own decisions mine are usually based off money. Good luck... Ill let you know in a few days or weeks how I made out. Hope I helped a little.

 

A good way to check your radiator is to simply get it to operating temperature, (thermostat open) and rest the palm of your hand briefly on various areas of the front fins on the all around the front surface of the radiator. If the thermostat is open, the surface temperature of the entire front of the radiator fins should all be the same. If you feel considerably cooler parts, then your radiator has clogging. This is how I tested mine, and fixed my 3 row core radiator. I had cool spots, had it rodded out and there was a lot of gunk, a real lot that could not be seen just by looking through the radiator cap opening. Problem solved for me. I had the same exact symptoms you are currently having with your cooling system. Zero problems now, works perfectly now.

 

thanks Ship and Shine. I will order a new radiator.

 

Stay away from radiatorbarn.com... IMO

 

double

 

So I thought the overheating problem was fixed. I drove about 2 hours this morning, and everything was fine. On the way home (the outside temp was about 91 in NJ) I drove for about 30 minutes and then the temp started to creep up. Until the temp when to red. Pulled over and turned the heat on and drove home. Any other ideas? I have replaced everything but the res bottle. I checked the upper hose and it was soft. I am not losing coolant from what I can tell. I guess the next thing is a possible head gasket on the exhaust side maybe letting in the hot gases? Or a crack on the heads? Any help would be great. I am guessing that the just running 35's and not re-gearing can’t be the problem. Or is it? I can’t even tow a boat if I wanted to.

Thanks guys

 

Have you ruled out a faulty temp gauge or sensor?

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I have not I guess. I should just replace the sensor.

Also, after driving when the jeep is up to temp the upper rad hose is firm. but this last time when the jeep over heat (and the time before) the upper rad hose was soft/squishy. Could that mean that my new radiator cap could be bad?

Recap: over heating on the highway (sometimes) after 20 or 30 minutes of driving. replaced everything minus the temp sensor. I am in need of help please.

 

I gave in and brought my Jeep to the local shop. He ran a Hydro carbon test from the radiator to see if exhaust gases are leaking in. came back okay. He said do anything flush. He was stumped. I drove over to the STS / Firestone auto shop and then said the same thing. I am going to replace the T-stat again and flush the engine again.

compression is fine.

Anyone have any other suggestions? I am out of ideas.

Thanks,

 

Forgive me if this was already suggested, there are some lengthy posts on this thread...

Have you verified there is a spring inside the lower radiator hose? I have heard that at high speed, hoses without a spring inside will collapse. Just another idea for you to consider.

Good Luck!

 

This brings me to the solution. Which is very weird? I have bought all Jeep Brand parts figuring they were on the Jeep when new and did not want any problems with cheap parts.

Yes I have the OEM lower hose with the coil inside on the jeep, but thanks for the heads up.

So I went to two shops and they said the head gasket is not showing signs of failure. And maybe just flush the coolant again. So it got me thinking that if the block and head gasket is good, then it has to be a flow problem. So I head over the Pep boys and pick up more coolant I have spent over 200 dollars in coolant so what the hell, worth a try. Then head over to Jeep for a temp sensor, maybe the one I have is bad. So new gasket and T-stat. Then I was thinking, maybe it is not opening up enough. So I head over to AutoZone and buy a few T-stats. All of the three that will fit. I throw them all in boiling water and see which ones open the best/farthest. The cheapest 4.99 did the trick. I was shocked, the two Jeep brand T-stats did not open enough to cool my Jeep and caused it to over heat. I returned the un-used T-stats to AutoZone and now left with two Jeep brand expensive T-stats.
Anyway, problem solved buy a 4.99 T-stat. Thanks for your help everyone!!!! I am signing up for a membership her. Tons of great info and help people!!

:cheers2:

 

Good to hear you finally solved your problem and can enjoy your Jeep again.

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I had the same problems/symptoms. I changed the thermostat and that didn't work. Flushed the radiator and found it was all clogged. New radiator and no more overheating.

 

Okay thanks good to know.