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overheating/overcooling??

H

hangubus

NAXJA Forum User
Location
California
91 Laredo 4.0-

1) overheats up hills, on hot days, idleing, and at speeds over 75mph. (220-240 degrees) i turn the heater on and if it still goes up i pull over and let it cool. Its boiled over once and im sure it would every time if i let it.

2) Temps. drop to about 160 degrees on cooler days when going down hills. To be honest i havnt spent a lot of time on this problem....very bussy college student. any help would be great! where to start?
 
Does the lower rad. hose have a spring in it? It could be collapsing. If it doesn't get one from the dealer. I couldn't find one anywhere else. Mine gets hot while idleing until the elec. fan kicks in. Make sure yours is working. HTH. JIM.
 
Recently fixed a similar problem with my 91 4.0. Turned out the main problem was the thermostat stuck open. After checking everything else, I also had a problem with the cooling fan not turning on without the ac running, had to replace the coolant temperature sensor on the water outlet.
Now it sits at 195* all day long with no problems. :D
Hope this helps.
 
sorry that didn't fix it for ya.
The next reasonable thing I can think of is either the water pump or mechanical fan clutch is bad or going bad, both are very common problems.
Could be as simple as the radiator is old and clogged up.

Someone who knows the cooling system better may be able to direct you on how to test the water pump and radiator.
There are enough overheating problems with the 4.0 XJ that someone here is sure to know the fix.

best of luck.
Paul
 
Check to see if there is anything blocking the airflow through the radiator (dirt, plastic bag, bugs, etc..).

If there is no airflow blockage and it's still overheating at speeds over 75mph then it's probably a plugged radiator or bad water pump. At highway speeds, the air flows through the radiator faster than the fans can pull air. Plenty of air and no cooling means no flow.

K
 
Cann't remember if 91 is a closed or open system, but if it is a close system they have a bad problem of the rad swelling up if it over heats causing reduced air flow threw the rad. Plus the closed system is bad about getting air pockets in them, causing over heating.
 
Low speed overheat is usually fan clutch, high speed overheat is usually radiator or water pump not being able to move enough coolant.
 
While looking for parts nows a time to look at upgrades I bought my alumanum rad for the same as a autozone special and it does a WAY better job.
 
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