Why does my car overheat only while driving uphill?

Factual Questions
1

Short version: My 1993 Jeep Cherokee overheats, but only when it runs uphill for an extended period of time. I can run it on the level indefinitely, in 90-degree heat, at 60 mph, with the a.c.blasting, without overheating or losing any water from the radiator. However, if I drive up from sea level to about 3,000 feet, the warning light comes on, and in response the motor shuts down. When I check the radiator the water is boiling and it is a couple of quarts low. I have had the problem “repaired” five times, by two different garages which have mechanics of excellent reputation, but they seem to be unable to get to the root cause. Help!

Long version: I live in Panama. I bought my Jeep used in 1995, and there were no problems when I bought it. In 1997 I had to replace the engine because the block cracked after I stalled out while trying to ford a river (that’s another long story), but the car ran fine after that.

This problem first developed in February of last year. The car overheated while I was driving on the flat on a highway near Panama City. I brought it in to my mechanic, who has always been reliable. He had to replace the head gasket, which had been burned out.

A couple of weeks later I drove it to western Panama, a seven hour drive. At the six-hour point, there are several long hills. The car overheated and stalled out at the top of one of the hills. Having no way to contact a tow-service (which would have taken many hours), once the engine cooled enough I put in more water and drove to the next major town (very slowly, refilling the boiling-over radiator at every gas station). The normally one-hour trip took five hours. At the garage there (which I was assured by locals was one of the best in town, and they did seem to be competent) they said there was a hairline crack in the head, and it would have to be replaced. Since they couldn’t do it right away, I flew back to Panama City. I flew back out a couple of weeks later, and they assured me the problem was fixed. But when I tested the car by driving into the nearby hills, once again it overheated at 3,000 ft. I took it back to the shop, then flew back to Panama City. I came back two weeks later, after they had “fixed” it again (and, they said, tested it by driving it into the hills). But when I tried it, it overheated again. At that point, I decided that I better just get the car back to Panama City, fixed or no. With plenty of spare water, and by topping it up when it overheated, I was able to nurse it through the hills, and then had no problem when I reached the flat. Back in Panama City, my own mechanic looked at again. He replaced the head gasket (burned out once again) and the thermostat (again). But when I took it into the hills again, it overheated at 3,000 ft! At this point the head has been replaced, the head gasket fixed, the thermostat replaced, the radiator cleaned, the radiator cap replaced . . .

Since then (seven months ago) I have driven the car to work, plus a few extended trips to places where I didn’t have to deal with hills. The radiator has apparently not lost a drop of water in all this time. My next option is to take it to the dealers, but I am reluctant to go to them because they are crooks and have blatantly ripped me off in the past. So before I do that, I thought I’d ask the Teeming Millions. So, all you automotive geniuses out there, what’s going on?

  1. Why does the car overheat only while going uphill? If there is a problem, why doesn’t it show up when I drive on the level?

  2. How is the radiator losing water? There are no obvious signs of a leak.

2

I’m stumped. Perhaps your radiator cap is bad and not holding 6 psi (or whatever) like it should? That’s all I got, good luck!

–Tim

3

I’m not a mechanic, but from personal experience with my elderly (87’) car, I’d have to say the problem is running your air conditioner. Going uphill puts extra strain on the engine anyway, and having the AC on drains power to my car, too, even just driving on a level surface. It has almost over-heated on me going uphill several times, so I did the sensible thing and stopped using the AC when driving up the steep hill near my house. While not the world’s best solution, it’s the most affordable one.

Wouldn’t the water from the radiator be condensation from running the AC?

4

Sounds like a problem for the Click and Clack Brothers: Car Talk on PBS. Ever listen to them? They’re on locally on Saturdays at 10 am, but times may differ in Panama. They also have a syndicated Sunday column. Give them a call, email, or whatnot. They may not know the answer, but we’ll all have yaks listening to them not know the answer. It’s even remotely possible that they will know.

5

They replaced the head gasket how many times?
I would be looking for something like timing problems.
I suppose brakes hanging up could cause it but after a year and three months they should have worn down so the problem would disappear.

6

Colibri, it can be any number of things and you would need to run some tests but I can give you one cause which happened (and is happening) to my car and it drove me crazy until I figured it out.

My car overheated once and after that started doing exactly what you are saying, except it was so seldom that I never cared. But it started getting worse and the car would overheat more easily. Note that it has nothing to do with going uphil, only with how much you are asking from the motor. The motor has to work much harder when you are going uphill.

Anyway, I could tell you the long process until I figured it out but I’ll cut through the chase and tell you: When the car overheated the first time, the head gasket was slighly damaged. Hardly noticeable but enough to communicate the water circuit to a cylinder. When the car overheats the pressure in the coolant circuit forces water into the cylinder. I was loosing water very slowly through the tailpipe! As this happened the car overheated a few more times and the gasket got worse and the problem got worse. I have been living with this problem for a couple of years now but the car is at the end of its life. Now it will overheat just too easily.

Just to confirm my suspicions I had a compression test done and sure enough a couple of cylinders are communicated.

My advice is to not let the car overheat again as the problem will get worse. If it is the gasket you will need to replace it sooner or later but if you are careful and know what you are doing you can get a lot of miles before you do it.

Good luck. I am looking for a new car :slight_smile:

7

Colibri, I missed the part about you already have the head gasket replaced. My hunch was right on track. Note that if the motor overheated badly the head may have warped and needs to be flattened again. Just replacing the gasket will not do as the new gasket will not last long. That’s the reason I am getting rid of my car.

8

Another vote for timing. Either you timing is retarded, or whatever works as a vacuum advance is working too well, causing the timing to retard too much at low vacuum (i.e., going up a hill.) Has anyone replaced any sensors, or the vacuum advance (if they still had those on Jeeps in '93 in Panama)?

I don’t know Jeeps, but you might check that the vacuum hoses are hooked up correctly. This can also throw your timing off.

This is a dumb question, but it’s not pinging under load, is it?

9

Here’s a couple of WAGs. I really know nothing about Panama, so I’m not sure how severe the hills you are talking about are, but if they are substatial, then it might be worth looking for.

If the hill is steep , and you tend to drive fast then you(or the car if its an automatic) will use a lower gear, which revs the engine a lot more, creating much more heat than on flat land driving. Also if the altitude is a fair amount higher, then the boiling point get lowered a fair amount. You may have a weak point somewhere in the cooling system that will leak when it gets to a high enough pressure. When you hit the boiling point it will boil fluid and steam out, creating a chain reaction where it loses a bit of fluid, then with the reduced fluid it cools less efficiently, which increses the heat, and boils off more fluid, etc. Until the car overheats. The fact that you keep blowing the head gasket might point to a defective block that can’t seal very well, and that might be the weak point.

10

Colibri:

Does the engine boil over and loose the water, or does it loose water and then boil over because you opened the radiator hot?

Every time before you use the vehicle, check that the radiator is full and the overflow resevoir is not filled to the top. You would have a bad cap, if the resevoir is full and the radiator is low. The cap is letting the excess out when hot, but not sucking it back when the radiator cools. Check that the line from the radiator to the resevoir is not cracked, and that the resevoir is not cracked. You then loose the overflow water and air sucks back into the radiator, when the radiator cools. Bit by bit the radiator loses fluid in either situation.

You have a engine leak if the radiator is not full and the resvoir is empty after finding the line and resevoir have no leaks. Don’t foreget that the frost plugs might be leaking also.

A simple check for a minor engine leak is to put alluminum foil over the radiator instead of the cap. Drive the car around, and the unpressurized radiator shouldn’t force water through the head leak. When you stop the fluid level should be checked that it is basicaly full while hot. The level will be low when cooled because the hot fluid will not go into the resevoir.

Some reasons for the engine to overheat the fluid. The radiator may also be cooling the transmision, and an added transmision cooler whould help. Is the radiator clean or are a number of the cores pluged. Does the airconditioner use the radiator for cooling at all. Radiators are sometime double purpose.

11

I’m going to suggest the frost plugs be replaced. At high altitude the cooling system should remain at 15 psi. A leaking frost plug would have less atmospheric pressure to counteract the cooling system pressure. Water dribbling out the frost plug would evaporate immediately. The loss would be almost nothing at sea level, but increase as your altitude increased. A frost plug is not very expensive, and not likely something a Panama mechanic would consider. The head gaskets could be the consequence of the engine over heating, and not the cause.

Let us know what happens.

12

Thanks a lot folks, some of these ideas sound like real leads. Especially the one about frost plugs, as it might well be something a Panama mechanic wouldn’t think of - and that’s the sort of thing I’m looking for.

A couple of points:

  1. I did have the head replaced - that was one of the first repairs that was made. There was a hairline crack in it. However, I am not sure if that was the initial problem, or whether the crack resulted from driving an overheated car for five hours. In any case, the problem was still present immediately after replacing the head.

  2. The change of altidude (and air pressure) itself could have something to do with it. However, I am not really going that high - sea level to only about 3,000 ft - so I am not convinced that’s the problem. I am more inclined to think it has something to do with the engine working harder.

  3. The radiator cap has been replaced, and was holding at least 14 psi the last time I had it checked.

  4. I believe the head gaskets burning out are a result of the engine overheating, not the cause.

  5. The radiator has been full before starting everytime I have tested the car by driving uphill. Somehow the system loses water - in a non-obvious manner, such as boiling over - in the course of driving uphill. However, it’s possible there is some problem in the link betweent the radiator and the overflow reservoir.

  6. I don’t think running the a.c. is the root of the problem, as the car overheats when going uphill even with the a.c. off. Anyway, around here I don’t want to have to shut off the a.c. every time I want to drive uphill!

  7. I will probably try running this by Click and Clack as well.

I’ll respond to some of the other points people have made once I have a chance to go over the answers in more detail.

13

My .02
You are right around the changeover year for the Cherokee’s cooling system from a closed to open unit. Don’t ask me what the differences are, because I can’t recall. I do know that the older ones were plagued with problems. If you want specifics, I highly recomend you go to one of the Jeep webboards on the net. I am sure you will get some help there. I don’t have any current URLs, but if you do a google search I am sure you will find some.

My solutions:

Check timing.

Put in either a cooler or NO thermostat.

Power flush the entire cooling system out.

14

had a simular problem, it was the waterpump impeller (it was wearing away, the fins were getting smaller.

Also if it is a AT, I suggest manually switching to a lower gear for hill climing as stated in your manual - it should make your jeep run cooler.
Do you have a temp gague - if not get one - they are cheep and you need one. When the temp starts climbing, turn off the a/c. if up some more turn up the heat to full and (vent) fan to full - slow down.

you should also check the fan and radiator flow (both air and coolent. Many fans have multi speeds (if electric) make sure all speeds are working.

15

Overheating is usually due to one of the following, so it’s really just a process of elimination:

Low coolant level
Bad thermostat
Radiator blockage
Radiator hose collapsing during acceleration

You also keep saying there is water in the radiator. But coolant needs to be a 50-50 mixture of water and antifreeze (which is usually glycol + rust inhibitors).

Lots of folks think that antifreeze is only important for climates where the temperature dips below 0 C. Not so, daddy-o. Depending on the vehicle, it can be just as important to use antifreeze in very hot climates. This is because the antifreeze will increase the boiling point of the coolant. (Some people will say this isn’t so because thermostats open around 180 F. But other parts of the engine may exceed that temperature.)

16

Yes, you’re right. I do refill it with coolant when I have the opportunity. But sometimes when it’s overheated on the road I’ve had no recourse but to refill it (temporarily) with water.

17

Remove the oil fill cap. Look at the underside that is in the valve cover. Is there a yellow, yellow green, or yellow brown coating on it? You’re getting blowby into the engine crankcase, if this is the case.

18

I agree with BERNSE…you gotta flush the entire cooling system.

Lots of times, minerals precipitate out of suspension in the coolant mixture and adhere to the coolant passages.
Not only do these deposits restrict the flow of coolant through the engine, the deposits themselves are somewhat insulating, preventing the heat from leaving the engine the proper way, thus the engine overheats.

Simply drain the system and refill with water and coolant flush. start the engine and turn up the heater all the way
(Antifreeze circulates through the heater core, remember).
Let the engine run for half-an-hour, drain, refill with plain water, run 5 minutes, drain, then refill with 50-50 mix.

Just to be on the safe side, run the heater to the max when going uphill…the heater core is essentially an extra radiator.

19

The head gasket situation gives pause for thought, beyond the good ideas offered so far.

Heads can warp or even crack for a number of reasons, usually due to excess heat but even in these modern times, a bad casting or even a slew of them from several batches can occur. Castings are aged or seasoned with heat and time to remove internal stress that could deform a head after machining, or unusual temperature variations during service.

Head gaskets have evolved a bit over the last 30 years, but certain principles remain the same. When torquing down a head to specs, shade tree mechanics normally need only observe rather simple basic procedure.

When there is a repeat problem such as yours, greater care should be given to solve at least the one while searching for the others.

Assuming flat mating surfaces on the head and block, clean threads on the nuts and studs, a high temperature anti-seize compound on the threads and faces to reduce friction (but will not cause future loosening of nuts, due to thread pitch and such), and a moderately accurate torque wrench, new gasket installations are normally successful.

Some manufacturors have made claims over the years that their gaskets don’t need to be re-squeezed after a car has run through a couple hundred miles of temperature fluctuations—balderdash! Heads should be re-torqued! There are some or even many who never do, and have no problems. You have other issues, so eliminating one possible problem could aid in finding the root evil.

On modern vehicles, labor costs to remove what is needed to access the head nuts can sometimes jack up the overall cost of an otherwise simple job, a bit.

None of this is to imply that your main problem does not lay elsewhere, but still a strong recommendation nonetheless.

20

I have never, ever retorqued the head on any vehicle I have owned. Be it new or used.