98 Grand Cherokee 4.0 Overheating Problem

PhilB,

You do not say if you were doing highway or around town/stop and go driving when it overheated. Knowing this would be useful in helping to determine the cause.

Given all that you had replaced 8 months back and that the cooling system was working fine till now, and assuming: 1) the pressure cap is working correctly, 2) the radiator is not clogged/has good flow, 3) the water pump/drive belt are good, and the thermostat is not sticking closed, then I'd start by checking that the cooling fan comes on when the engine warms up like it should. This is especially important if doing stop and go/around town driving when there is limited airflow through the radiator.

If you find that the fan is not operating, then check the electrical connections/fuses, coolant temperature sensor (CTS), fan relay, and the fan motor. If this is like other Chrysler vehicles, you should be able to simply unplug the connector from the CTS and the fan should default to "on". You should also be able to turn on the A/C and see both fans turn on immediately.

Good luck

Bob

Thanks. Let me add some more info.

I was highway driving, but I'm located in the NYC area, and actually the problem occurred while I was on the NJ Turnpike near Hoboken, so highway driving in this case = stop-and-go driving.

I drive mostly city (stop and go) and now that I think about it the only reason why it hasn't overheated until yesterday was probably because my trips are pretty short (5-10 minutes).

The water pump belt is new, as is the radiator cap. At the time, I did a full tune up so the plugs, wires, distributor, etc. are all 8 months old as well. The motor coolant passages was flushed at the time, and flow was good. The radiator is brand new (when I installed it) so I don't think it would be clogged. The coolant fan is belt driven, not electric, so an electrical problem can't be the cause.

There's nothing else to the system. The overflow tank is fine (not cracked), the hose to that tank is fine also. I'm not seeing any white smoke from the exhaust, so I don't think I'm burning coolant.

I think the only thing this could be is that the thermostat is sticking closed.

That's a logical place to start and a cheap fix to boot.

Steve B.

PhilB

That or a head gasket ... I'd definitely look over the whole system and if everything else is good, then try replacing the thermostat first.

Bob

when I've had a stuck thermostat in the past the top hose was cold and the bottom hot (or vice versa, don't remember). and i had no heat. but your symptoms sound close to what i had. sine you were stop and go i don't think your water pump is sucking the bottom hose shut. its also best to make sure your fan is coming on.

Let's just say it's the head gasket. I haven't done that much work on a motor since I tore down a Boss 302 Ford engine when I was a teenager (not a very long time ago but long enough). I learned a lot, but I also had a summer full of time, no job, house, wife, kids, etc.

I assume given the vehicle is a 1998 with 160,000+/- miles on it, it wouldn't make sense to have the dealer perform the operation as the cost would be prohibitive. I assume the local service station would be costly as well. Is it feasible to change the head gasket (and I assume recondition the head while I'm at it) in my own garage? Are there special tools or techniques needed, or is this just the removal and re installation of a lot of parts?

I'll check my service manuals tonight, but am just wondering if anyone has first hand knowledge of this procedure.

Thanks, Phil

Well with a sever overheating like you had it isn't unheard of for the head to warp and the head gasket to blow soon after... I'm going to remain optimistic for you though and hope it's just a thermostat.

I wouldn't hesitate to try a head swap on that vehicle. Worst case scenario you can't do it and have to tow it to a shop... you aren't out much except a two truck fee. You can have a machine shop redo the head or just buy a reman head. Add a gasket set and a half dozen random parts that break when you look at them sideways. Sounds like a good weekend project if it comes to that.

Steve B.

Thank you.

I have a bit of mechanical experience, even though I have an office job. But I have less time than I do know-how, and that's what's concerning me, how long it will take.

I checked the jeep out this evening. At first, the it ran rough, started overheating (at least the temp went up) and stalled on me, probably within 6 minutes after a cold start. I let it cool 15 minutes, then started it again, and the 2nd time it ran fine. The fan was running fine, the belt is running fine, no squeaks or anything, just normal. The 2nd time I started I just let it idle and got under the hood. The top radiator hose was soft until the car came up to temp, then I felt the pressure in it, so it seems to me that the thermostat was working at that point. Could be the the thermo works intermittently, which explains what happened when I drove home last night (see top post).

This weekend I"ll change, or just remove the thermostat altogether.

But....when I shut the car, I heard a hissing sound. Upon some exploration, it seems to be coming from below/behind the water pump, below the head. The hissing sound continued for awhile after the car was shut down, like something was depressurizing or re-pressurizing.

The car has a/c, and it's blowing cold, wonder if that's the source of the sound.

I love my Jeep, and don't want to give it up. The thought of getting a new one is nice, I'd love a Wrangler with a 6 speed. The thought of a new car payment is not nice.

Anyone recommend a shop on the east coast specializing in Jeep rebuilds....if I'm gonna do the head, I may as well have the entire thing looked after I suppose.

Phil

If the A/C was running, then the hissing sound is normal and may simply be the A/C pressure equalizing itself when the compressor is shut down. Try the same experiment with the A/C off/not running.

Bob

This weekend I"ll change, or just remove the thermostat altogether.

But....when I shut the car, I heard a hissing sound. Upon some exploration, it seems to be coming from below/behind the water pump, below the head. The hissing sound continued for awhile after the car was shut down, like something was depressurizing or re-pressurizing.

The car has a/c, and it's blowing cold, wonder if that's the source of the sound.

Phil

That is the first step I would take, but if you are waiting for the weekend don't drive the vehicle until then. You might get away with one good overheat but don't press your luck,

Probably just the a/c. Keep an eye on the water level once you start driving it just to be sure.

You are being courted by the she devil known as "might as well". Might as well will cost you a fortune on a job like this if you don't keep her in check. Doing the top end, might as well do the bottom end. Cooling system is open, might as well replace the radiator and water pump and all the hoses. Look at all these old rubber lines, might as well replace them all. Watch out for this temptress...

Steve B.

You couldn't ask for an engine that's much easier to do a head gasket on than a Jeep 4.0. Fortunately both the head and block are cast iron, so its much more tolerant of overheating than an all-aluminum or and aluminum-headed engine.

The most sophisticated tool it would require is a torque wrench.

Ok, we seem to be good. The hissing was the a/c. The overheating was the thermo, I removed it this evening, I had another gasket on hand but not another thermo, so I just pulled the thermo out, cleaned the goose neck, re-gasketed and put the goose neck back on. Ran it for

20 minutes or so and everything was cool. We'll see what the next few days bring.

Thermo was only a year old, and very rusted. Don't understand why, I run with 100% Prestone, no water. So I'm sure there are other issues. Still weighing my options with this Jeep.

Thanks everyone for your help, and encouragement.

Phil

hey Phil you live in an area that gets cold in the winter? and if you do , do you run straight anti-freeze in the winter as well?

Ok, we seem to be good. The hissing was the a/c. The overheating was the thermo, I removed it this evening, I had another gasket on hand but not another thermo, so I just pulled the thermo out, cleaned the goose neck, re-gasketed and put the goose neck back on. Ran it for

20 minutes or so and everything was cool. We'll see what the next few days bring.

Thermo was only a year old, and very rusted. Don't understand why, I run with 100% Prestone, no water. So I'm sure there are other issues. Still weighing my options with this Jeep.

Thanks everyone for your help, and encouragement.

Phil

Yes, NYC - freeze/thaw. I run straight anti freeze winter/summer. Although, come to think of it, the Prestone container I think says "do not add water, 50/50 mix". I have to check, I may be confusing it in my mind with the coolant I use for another car.

Thanks.

You shouldn't run antifreeze any higher than a 70/30 ratio. 50/50 gives you protection to -34. 70/30 gives you protection to -84. Straight antifreeze freezes at -8 and it doesn't carry away the heat as well as properly mixed antifreeze which can cause overheating problems.

Steve B.

phil, not having a thermostat in it my really hurt your fuel milage . computer thinks it s cold all the time and runs rich

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Thanks, intend on putting a new thermo in, just didn't have one on hand to run this test. It's a PIA to change with that fan shroud in the way, but if I keep the Jeep I need to do plugs, oil etc, so I'll deal with it all in one sitting.

Thanks.

Np. It's the 50/50 mix, I checked the container last night.. So I think I'm covered. Am starting anew thread, went and took a new Wrangler and Grand Cherokee for a test drive yesterday.....

Phil

Don't understand why, I

Why do that? You realize that straight glycol has significantly less heat transfer capability than a 50/50 mix, don't you? And also the corrosion inhibitors are intended to work WITH water, not without it.