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another 88 mj overheating


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anybody have any idea why my 88 2wd is overheating

 

the setup

88 lwb 2wd with 2 in budget boost and 31's with 3.55

converted cooling system to open last year

newer style 2 core radiator

removed heater valve and ran straight from waterpump to core and back

electric fan wired to switch

 

the problem

on extended highway runs the temp gauge slowly climbs and does not stop climbing until i slow down below 60 mph. It does not matter if i turn on the electric fan or not. It does not overheat around town at all.

 

 

this problem has been getting worse slowly over the last 3 months. I don't lose any coolant and can't smell antifreeze in the exhaust. mileage is slipping alittle but not bad. I am at a loss as to what could cause it to overheat at highway speeds and not around town.

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I would suggest getting a thermal gun and run it on the hiway untill it starts to overheat a bit and pull over quickly and check the difference in temps at the head and the radiator, it might help you get an idea of where to start looking for answers. Also ive heard cases of water flowing to fast through the radiator to cool it properly, ussually because someone left out the thermostat. It could also be that your cooling system is working its butt off at all times and when your around town driving it has just enouph guts left in it to keep you cool under light load situations but when you get crankin on the hiway it puts the heat generated over the top of its abilities. something like a heavily deposited (hard water and such) block will keep water from flowing where it should and limit your cooling system. Just a couple things that crossed my mind. Good luck oh ya what motor?

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If you have replaced the lower radiator hose with an aftermarket one, the hose will collapse at highway speeds, restricting the water flow. The reason it collapses is due to the high suction in the system at those speeds.

 

The origional AMC hoses had a spring inside to keep this from happening. I do not know if you can get an origional hose, the auto parts stores do have hoses that have an external spring, but I could not get it to bend enough to work. I ended up buying a hose meant for a chevrolet and pulling the spring out, then re-installing the spring into a "springless" bottom hose.

 

My story is here:

 

http://www.comancheclub.com/forums/viewtopic.php?f=2&t=25205

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