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Old September 29th, 2013, 12:46 PM   #1
yyj87
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Default 4.0 cooling issues

97 4.0l with a pile of miles in a 91 wrangler.


I started having cooling issues a month ago, it runs 210 on the dot 50% of time. Engine load, outside air temp and vehicle speed do not seem related in any way.


When it is started cold it will rise in temp to 240* then drop like a rock too 100* and slowly climb back up. At an idle or while driving it bounces between 200* and 230* with occasional spikes to 250*

3 weeks ago I drained the coolant (looked chunky orange and gross)and refilled with a mixture of vinegar and water, ran it for an hour and drained it and refilled with distilled. I flushed it with distilled 3-4 times, the last time I drained it all looked clean. I replaced the tsat refilled with 50/50, burped it and drove it expirencing the same issue. I can see a good even flow of coolant through the top of the rad, it doesn't over heat to the point of blowing the cap off the resivour. I pressure tested it and it passed. No milk shake, no funny colored spark plugs, no oil in the coolant.

The water pump is a year old.

My thermometer tells me the guage reads accurately.

I'm at a loss...
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Old September 29th, 2013, 12:56 PM   #2
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I'd guess either you have air in the system, or a leaking head gasket. You said you pressure tested it, but maybe it leaks when hot?
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Old September 29th, 2013, 01:17 PM   #3
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Faulty temp sender or gauge?
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Old September 29th, 2013, 01:28 PM   #4
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I'd guess either you have air in the system, or a leaking head gasket. You said you pressure tested it, but maybe it leaks when hot?
I pressure tested it cold and hot. seems like I would have fluids mixing or a funky spark plug if the head gasket were bad. Leak down test on all 6 cylinders came back dead even.
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Old September 29th, 2013, 07:24 PM   #5
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Check and see if radiator is same temp from to to bottom, also check the fans
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Old September 29th, 2013, 10:56 PM   #6
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Check and see if radiator is same temp from to to bottom, also check the fans
I rigged that fa do that it is always on and it made no difference.

I'll check rad temps tomorrow.
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Old October 17th, 2013, 08:36 PM   #7
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Replaced water pump again (I found it had a grimy bearing), replaced head gasket, new rad (slip of a wrench doh) and put another new tstat in.

Same symptoms!

I'm still at a loss. It still pressure tests good and the rad new rad is doing its job.
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Old October 17th, 2013, 08:45 PM   #8
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block look clean or is it full of scale ?
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Old October 17th, 2013, 10:49 PM   #9
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what belt set up are you running ? v belt or serpentine, then tell me what waterpump your running tj or yj ? the impellers spin a different direction and will overheat if its not spinning the correct way
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Old October 17th, 2013, 11:27 PM   #10
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Sounds like an air pocket and or bad thermostat.
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Old October 17th, 2013, 11:42 PM   #11
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Is the belt routed correctly letting the water pump spin in the right direction? I know it sounds stupid, but have seen it numerous times.
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Old October 17th, 2013, 11:49 PM   #12
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Just looked at my Chrysler jeep service manual for my 2000 xj and quote when coolant temperature reaches approximately 103c(218F) or when air conditioning is requested,the power train control module(PCM) provides a ground path for the fan relay.when coolant temperature drops below approximately 98C (209F) the PCM opens the ground path to the relay. So your jeep is running they way it should be. Your thermostat starts to open at 195 F and the cooling fan comes on at 218F so your good
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Old October 18th, 2013, 12:41 AM   #13
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^^
this
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Old October 18th, 2013, 07:48 AM   #14
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Quote:
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block look clean or is it full of scale ?
It was not scaled, it was dirty but not nasty

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Originally Posted by sandfox4 View Post
what belt set up are you running ? v belt or serpentine, then tell me what waterpump your running tj or yj ? the impellers spin a different direction and will overheat if its not spinning the correct way
Yj water pump, it flawlessly for 2 years.
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Old October 18th, 2013, 07:50 AM   #15
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Quote:
Originally Posted by WACKO1 View Post
Just looked at my Chrysler jeep service manual for my 2000 xj and quote when coolant temperature reaches approximately 103c(218F) or when air conditioning is requested,the power train control module(PCM) provides a ground path for the fan relay.when coolant temperature drops below approximately 98C (209F) the PCM opens the ground path to the relay. So your jeep is running they way it should be. Your thermostat starts to open at 195 F and the cooling fan comes on at 218F so your good
The block is newer but pcm, much fan & everything else is 1991 yj.
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Old October 18th, 2013, 07:52 AM   #16
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Originally Posted by 88yjproject View Post
Is the belt routed correctly letting the water pump spin in the right direction? I know it sounds stupid, but have seen it numerous times.

While burping it if I bump the throttle it draws the coolant down in the rad.
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Old October 18th, 2013, 08:48 AM   #17
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Quote:
Originally Posted by WACKO1 View Post
Just looked at my Chrysler jeep service manual for my 2000 xj and quote when coolant temperature reaches approximately 103c(218F) or when air conditioning is requested,the power train control module(PCM) provides a ground path for the fan relay.when coolant temperature drops below approximately 98C (209F) the PCM opens the ground path to the relay. So your jeep is running they way it should be. Your thermostat starts to open at 195 F and the cooling fan comes on at 218F so your good
Reread the original post. The temps are a bit higher than what you posted and not normal operating temp at 250. Assuming the gauge is correct.
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Old October 18th, 2013, 11:30 AM   #18
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Reread the original post. The temps are a bit higher than what you posted and not normal operating temp at 250. Assuming the gauge is correct.
I checked gauge with a therrmomiter touching the head next to the sensor. It was +/- 5*..

Guage was the first thing I tested.
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Old October 18th, 2013, 11:45 AM   #19
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Replace temp seńsor
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Old October 18th, 2013, 04:37 PM   #20
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Replace temp seńsor



I have confirmed that the sensor for the gauge is reading correctly and I have a mech fan.

Please explain....
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