OT tech question...Jeep - PeachParts Mercedes-Benz Forum

davestlouis · #1 08-11-2007, 11:29 PM

I just bought a 1997 Jeep Cherokee (little square 4 door wagon), 4.0L, automatic, 4wd. It has been HOT here and I have a cooling issue. It has done the following twice, only in the heat of the day, in bright sunshine:
-toodles along at 210-215 degrees, with the A/C blasting, for 30+ miles
-out of the blue, the temp needle climbs to 260, within 5 seconds or so, just a quick sweep of the needle
-if I turn off the A/C it drops, right back to 210ish, in about 5-7 seconds.

I refuse to believe that the coolant can change temp that quickly. The first time it happened, I stopped, popped the hood, and the coolant wasn't boiling in the overflow tank, wasn't making any gurgling noises, wasn't smelling "hot"

The second time, my wife pulled off, parked, and she said it puked some coolant on the ground...I had filled the overflow to the top the evening before, so I'm not sure if it was overheated or not.

The oil looks good, there is no sign of oil in the coolant, just can't tell what's going on. The only other thing that seems a little weird to me is that the car goes from stoen cold to 150 degrees before I get out of my subdivision, which is the quickest of any car I've ever had.

Any thoughts?

No pinging, no weird smells, none of the symptoms I associate with overheating.

Matt L · #2 08-12-2007, 12:28 AM

A bad electrical ground between the engine and body can cause a high temperature reading on many vehicles. I don't know if your Jeep is one of them.

An easy way to tell is to increase the electrical demand to the body and watch the gauge. The headlamps are a good candidate. Yours sounds like it is intermittent, so you might try turning the lights on and off when it displays this symptom.

If you filled it to the top and the engine really was hot (but not necessarily overheated), losing coolant upon shutting the engine off is normal.

BamaMB · #3 08-12-2007, 12:54 AM

You may have a sudden passage between the combustion chamber and the coolant passage. Hot combustion gases could be entering the coolant system and giving you the high temp readings. Check the torque on the head bolts, but you may need to pull the head and check to see if it is warped.

kerry · #4 08-12-2007, 09:47 AM

I'd try using a non-contact thermometer in the vicinity of the temp sensor when it happens to see if it is a true reading or a faulty sensor.

davestlouis · #5 08-12-2007, 10:39 AM

I'm finding on Jeep forums that this is fairly common. Seems the cooling system is marginal when new, and with age the radiator gunks-up and give coolant temp spikes. Further, these engines are prone to air bubbles which are tough to burp out. There's no eivdence of a head problem...yet.

The solution seems to be, start with a thermostat and rad cap, then a new 3-row radiator if a good clean-out doesn't work.

I started with this forum because with other brands of cars that I've had trouble with, good tech advice is tough to find. The Jeep guys seem to actually analyze tech questions and try to give substantive answers, much like the people on this forum.

TwitchKitty · #6 08-13-2007, 12:14 PM

260 sounds high, 245 is nothing.

I bought another Cherokee, 2000 this time. I missed my last one as soon as I sold it.

The advice to check with another thermometer is good. Clean your radiator/condenser with chemicals like mag wheel cleaner. A dirty radiator will not dissipate heat as designed. Clean the fan blades, dirty blades don't move air as designed. Watch and listen to your fans for proper operation, feel for air flow. The air off of your radiator/condenser should be hot. Check the specific gravity of your coolant. Pressure test your cooling system.

I have had several Cherokees over many years but very few problems with any of them.

Change your transmission fluid before it looks like it needs it. Transmissions make a lot of heat when they are not exactly right or are working too hard.

PaulC · #7 08-13-2007, 12:19 PM

A lot of radiator hoses have a metal coil spring-like insert that prevents the hose from collapsing and impeding coolant flow under certain circumstances. Sometimes this spring is not replaced when a hose is replaced, or corrodes after many years. Does the Cherokee require such a spring? Might be worth looking into.

PS: Did Jeep ever specify a heavier duty radiator for special use/export models?

mrsbnz · #8 08-13-2007, 07:22 PM

Try burping the rad.

LUVMBDiesels · #9 08-13-2007, 07:28 PM

Quote:

Originally Posted by davestlouis

I'm finding on Jeep forums that this is fairly common...

...The Jeep guys seem to actually analyze tech questions and try to give substantive answers, much like the people on this forum.

I am looking for a good place to go to talk about the '74 CJ...

I also think that what you are seeing is due to air in the system. The Suburban used to do the same thing. Everything looks good and then BAM the needle has swung all the way over and the stupid "check gauges" light has come on. Then just as quickly it would swing back. I spent some time getting the air out of the system and now it behaves normally, for a Chevy that is

Try running the heat on full with the radiator cap off. Rev her a few times to see if you can push some air out of the system. You might also want to do the trick of removing the upper hose from the radiator and filling the block that way.

PaulC · #10 08-13-2007, 07:29 PM

Do you have auxiliary lights or a winch that may be partially obstructing radiator airflow?

JD Tetterton · #11 08-13-2007, 07:38 PM

I own an 89 jeep pickup with the 4.0. I have had the truck for the last 10 years. Great truck but as mentioned the coolant system is very prone to air bubbles. The best way I have found to keep this under control is to park the truck on a steep hill (with the front up) remove the cap and bring the motor up to temp. You can see the air bubbles coming up. I only have had to do this maybe once a year. The truck has 189,000 miles with no major work! I love that thing. Hope this helps.

J.D.

mrsbnz · #12 08-13-2007, 07:41 PM

http://www.pirate4x4.com/forum/

davestlouis · #13 08-17-2007, 12:04 AM

I really like these little Cherokee's...they are compact, have great visibility all around and seem to run a lot stronger than the '02 Grand Cherokee my wife has with the same 4.0L engine. The thing I had not anticipated was my teenagers' friends oohing and aahing over it, and asking if I would sell it...several of them want to make a mudder out of it. A coworker just bought a similar one, but with the 2.5L 4 cylinder in it and he is hating every minute of it, calls it an underpowered little turd. I haven't drien it for several days, I've been working too much to play with the cooling system...maybe this weekend I'll get a little time to tinker with it.

TwitchKitty · #14 08-18-2007, 01:47 PM

The Grand Cherokee weighs a thousand pounds more but has the advantage of coil springs on all four corners. The Cherokee, with coils front and leafs in the back, will always have unbalanced suspension action.

LUVMBDiesels · #15 08-18-2007, 05:25 PM

Quote:

Originally Posted by mrsbnz

http://www.pirate4x4.com/forum/

Thanks for the link!