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2000 JGC V-8 overheating/ occasionally only !!

I posted here about this before, and got some good info.

Symptoms again.......... the car never overheats in town. Does not overheat sitting at a redlight.

On the highway, at 70 mph or so, the engine runs about 10-15 degrees over what it normally does. Normally, it runs between 190-200 degrees, and now runs from 200 to 215 degrees. (Some will say this is normal. Maybe, but not for my car. First 120K miles, it ran cooler).

At times, if I go up a long, steep grade, it will overheat rapidly, up to

250-260..... it has not been boiling over. If a long steep grade is 2 miles long, it will heat up like this, and then after the road levels off, the engine will cool down to 210 degrees after 2 or 3 miles.

Here is the funny part............ it will not do this every time I go up a steep grade. I can do the same grade two times in one day..... same outside temperature, and one trip it will run 210 degrees up the hill and on the second trip it will almost boil over. So, it is not consistent.

Here is what I have done. New thermostat, 190 degrees. New coolant, and flushed radiator. One year ago installed new fan clutch. New serpentine drive belt (fan belt)

Jeep has original water pump and radiator. Mileage is 130K. Engine is fine.

I am not a mechanic, but I think there are just two main things left. I think the water flow is restricted by a clogged or bad radiator, OR I have a defect in the water pump.

Questions: How can I diagnose the most probable culprit. the water pump or the radiator?

Can't radiator shops do a flow test on the radiator ? Would that test also give a hint about the operation of the water pump ?

Are there other possible mechanical problems other than the water pump and radiator, given the steps that I have taken already to cure this problem ?

If you had to guess , would you vote for a new water pump or a rod-job or new radiator?

Remember two things...... the car NEVER overheats at idle or at slow speed. It only overheats at higher speeds, going up steep hills. And, the overheating is erratic. The very same conditions/ temp/ road grade/ etc will not give the same result each time.

Whaddduuuyaaaa think ??

Thanks !!

--james--

Reply to
James
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Reply to
L.W.(Bill) Hughes III

Bill, do you think the thermostat only malfunctions when going up a steep grade ??

I had thought about the radiator cap and took it off today and looked it over. It "looked" fine, and the rubber gasket looked fine.

How can one test for 15 lbs ?? Or, as a general rule, how can I know if the radiator cap is ok ?? Can that part only be bought from Jeep ?

--James--

Reply to
James

Reply to
L.W.(Bill) Hughes III

Are you sure the temperature sender is working properly?

Next time your overheating, turn on the inside heater on full blast and watch what happens to the temperature.

The pump can be wearing, but that's not usual. A clogged radiator is alway a possibility. Basically you just drain it, and look inside.

I just replaced my radiator after it sprang a small leak. Didn't look that bad but there was some buildup. Not bad for a 1993 ZJ.

Reply to
DougW

My nickle is on the clutch fan. I know it was replaced 1 year ago but I strongly suspect that is is the culprit here. Its engagement temp is too high and thats why sometimes it cools and sometimes not. Ram air a lone will not always cool the engine especailly a V8 in a GC because it is a tight fit. At the link below you will find instruction on have to tweak the adjustment of a clutch fan because most of the time a little twaeking will cure them.

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TheSnoMan.com

Reply to
SnoMan

Sno man, I had been under the impression that a problem with the clutch fan would make a car overheat at idle and slow speeds, such as when stopped at a red light. Maybe I am thinking about the electric fan though..........

I didn't know they could be adjusted. I will study the site.

Thanks !!

--James--

Reply to
James

A clutch fan is centrifical and bimetal thermostat controlled. It engages when the bimetal control lets fluid into clutch disc area faster than centrifical force can remove it. This is why it can sometimes cool better at low speed because the centrifical forces are not purging fluid from it faster than it is being replaced. Also at low speeds the engine is making less power on average and needs less cooling generally. When you put a big V8 in a small car the cooling system has to be just right for it to keep its cool. I would consider a electric fan as a last resort because it cannot come close to matching the air flow capabilies of a engine driven clutch fan. To do so would require more electric power than you vehicle can produce to sustain it.

----------------- TheSnoMan.com

Reply to
SnoMan

Reply to
philthy

I had this EXACT problem 10 years ago with a Ford vehicle.

Problem: clogged radiator. After replacement, heat was never a problem again.

Reply to
Outatime

Reply to
philthy

Not alway true, all it does tell you if the fluid has leaked out of it because it leaks in to clutch area normally when it sits overnight after gettting warm. It does not tell you if the bimetal coil is working properly for your tempature conditions.

----------------- TheSnoMan.com

Reply to
SnoMan

I do not think so here because at times is runs cool under same conditon as it sometimes runs hot. If raditor was plugged it would be hot all the time. Also, anoth thing, if you do not here the clutch fan humping when gauge is climbing you know it is not doing its job.

----------------- TheSnoMan.com

Reply to
SnoMan

As I said earlier, I had this exact problem 10 years ago. It often ran very hot, other times it ran cool. As the OP mentioned, it runs hot after freeway driving, as mine did. Experience has taught me that a plugged radiator will not always run hot all of the time.

Reply to
Outatime

Clutch fan failures are a LOT more common than plugged raditors these days. 15 years around I had a old plow truck start over heating one day plowing snow for no reason when it had been doing fine for a few years. It turned out it was the clutch fan because it was not cooling properly with the disturbed air flow from plow in transport and engine was over heating. Replaced clutch and all was well.

----------------- TheSnoMan.com

Reply to
SnoMan

The clutch fan would *seem to be* eliminated, because of the freeway only overheating. But, and I don't have one of these vehicles, there is a lot of equipment under the hood of a JGC V8, potentially blocking the air flow. SnoMan could be right. Now in my Suburban I can drive all day long on the freeway without any overheating, but GM left some room under the hood. ;^)

Earle

Reply to
Earle Horton

There is a misconception about clutch fans not providing any highway cooling. Sometimes it is needed because ram air does not do the job. On hot day i can hear the fan come in from time to time on my old suburban and my 2000 K3500 even on highway. Because of this my temp gage never exceeds 210 at any time and rarely even gets that high. I will gladly have a like extra fan noise from time to time from a agressive clutch fan that keep engine temps stable rather than a conservative clutch fan setting that lets temps spike wildly before it engages. I have had to "tweak" the clutch fan bimetal coil on my old burb a few times due to it aging but it still the original one otherwie after 17 years and over 180K miles.

----------------- TheSnoMan.com

Reply to
SnoMan

I will have to agree.

We put a new fan clutch into our Cherokee a few years ago and it recently started overheating (red light on, no blow out) sometimes on the highway, particularly on this one 20 mile uphill run.

So I check everything and then just because, stopped it with the light on and tried to spin the fan. The sucker spun free!!!! It was a new OEM one too.... Grr...

I am going to try that spring indexing, thanks for the write up.

I am almost tempted to index the spring for full on so the fan works all the time...

The vehicle either sees a '5 minute to work drive' or a trip on the highway.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
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Reply to
Mike Romain

Just remember, I little bit goes a long way with adjustments. I would suggest that you do not go from broke and figure on maybe having to remove it a time or two to get it just right. Try about 1/8 inch index cahnge for starters in your case and go from there. 1/4 inch is a very big adjustment here that may leave it engaged almost constantly at times. The weakness of the bimetal coiled clutch fan concept is that it reacts to the tempature of the air coming through radiator core not coolant so on a cool day it is possible to have it run hot and not have fan engage because the air is still not that hot because it started out cooler. WIth proper tweaking you can usually find a good compromise.

----------------- TheSnoMan.com

Reply to
SnoMan

Holy Jeezus.

Do me a favor and either explain to me how a fan clutch will work properly with a plugged radiator (intermittently or not) and sort this out:

"The weakness of the bimetal coiled clutch fan concept is that it reacts to the tempature of the air coming through radiator core not coolant so on a cool day it is possible to have it run hot and not have fan engage because the air is still not that hot because it started out cooler."

...or please stick to the Chevy Plow Forum.

Jon

Reply to
Jon

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