98 Grand Cherokee 4.0 Overheating Problem

Have a 1998 Grand Cherokee, with about 158,000 on it - practically
still new.

I replaced the radiator, top and bottom hose, water pump, thermostat
and all gaskets - all new parts. Everything worked fine for about 8
months. Last couple weeks, starting running a bit hot, no fluid loss,
no leaks.

Yesterday, it overheated bad, pressure built up so much that the
bottom rad hose blew off. Pulled over, let it cool down, put the hose
back on. Refilled with fresh anti freeze. Got maybe a mile, and it
over heated again. No fluid loss. Let it cool. Started out again, the
temp indicator went fully to the right, but I had to get home, so I
went for it.

Every so often, the temp indicator would drop to about 220, then red
line. Went back and forth like this the rest of the way home - maybe
12 miles.

It was clearly running hot, and overheating, so I don't think the
problem was the temp sending unit.

Bad thermostat maybe? I'm thinking maybe it was getting stuck closed,
then finally opening and I would see the temp drop, then close up
again.

Any other thoughts on this?

Thanks in advance.

 

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

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.

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

 

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

 

PhilB wrote:

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.