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90 Overheating


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I built a 1990 4 door for my brother. I picked the rig up for 500 so I could have the rear axle with LSD and discs. I put my 88 axle in and put a new upper and lower plenum gasket in. new rear main seal, shocks and a coolant temp sensor. We also put the heater core, dash, stereo seats and other misc parts from his 90. I did the timing and some other stuff. I drove the rig form Fort Bragg,CA to Astoria, OR. The whole time the rig was hot, did not boil or get into the red though. It get almost to the line and stays there. Since this I have replaced the water pump and the thermostat with no change in the operating temp. It has oil, water and all the other fluids needed. Compression is good on all cylinders and I have flushed the system twice, it drains clean each time. The radiator is from his 90 that ran cool all the time. The radiator does not get evenly hot when the car is hot, and there is even some cold spots on it when the coolant is steaming over to the recovery bottle. Any help? I am completely confused.

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I think you are making the mistake that the dash temperature gauge is actually reading acurately. There are two temp sensors, one for the gauge, one for the ECU; which one did you replace? Are you sure it was the right sensor and/or was good? What is the output of the sensor, does it fall into proper range? (assume 1994 FSM values if it is the same part #)

Have you checked the coolant temp independently with something like a meat thermometer?

If it drives, runs fine, doesn't blow hoses or boil over, how hot is it?

 

B

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It boils over, not sure how hot actually. I replaced the one for the ECU not the dash. The heater intermittently goes cool then back to hot. Really confusing.

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Maybe the cooling system has air in it? Try bleeding it and topping up; short of a clogged rad (unlikely if the coolant comes out clean) I can't think of what else would let the rad have cold spots.

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Best way to get the air bubbles out of the cooling system is park on an incline so the nose of the Pathy is up higher thus the radiator is at the high point so any air towards the back of the heater core will force it's way towards the radiator cap end. Only open the radiator cap when it's not hot, then run the engine and top it up, wait for the radiator to 'burp' out any air bubbles and keep filling until it stops belching out anymore air bubbles.

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may not need a radiator, wouldn't hurt to replace it being a 90 but, when my old 94 was running hot, not real hot but above or near half, I replaced the fan clutch and it never went near half again, that was driving mid summer in too hot Florida.

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Fans electric or clutched work only up to 35mph. After that speed the air coming across the radiator is faster than what they pull. So with that driving under normal conditions would lead someone to the problem. Armadas had a huge cooling problem with the ac on. So I used to install a heavy duty fan clutch that would actually lock up at a certian temp. the downside is noise

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  • 3 weeks later...

I might try the fan, the thing was hot driving from CA to OR at all speeds(about 3/4 on the meter). If not, im thinking of just going with some E fans, pretty cheap on EBay or amazon.

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maybe too hot a thermostat, and try cleaning the vanes of the radiator, if they are all clogged and not allowing air flow the heat can't dissipate.

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I would replace the radiator. I know you said the other truck ran cool but @!*% happens. Also have you checked the water pump?

Edited by adamzan
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my 5 cents

 

check your top and buttom rad hoses, 1 should be a little cooler then the other as the radiator cools it, if you get extreme temp differences or as you say cold spots then there is a interruption in the water flow,

 

you can try a simply trick to see if its your cooling system or your engine that is the issue, when the temp goes up turn your heater & fan to full if the temp comes down most likely your cooling system and the only way to fix it is systematically changing/replacing parts

including

 

thermostat check/replacing

radiator honing out or new replacement

 

if it doesn't go down it possibly your head or faulty gauge

 

my sister was having similar issue we didn't find what was causing her over heating until it was blowing big white clouds out of her exhaust and she almost hydro locked the engine 2G & a family friend later the car drives better then before,

 

that was my 5 cents hope you get it sorted

 

Mike

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It has a brand new thermostat and water pump, The heater works but does not effect the temp of the truck and occasionally the heater got cold when driving and the engine was really hot. I think I'm gonna have him put a new radiator in it. There has been no smoke and compression was well within spec. so I'm taking heads off the cause list for now.

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  • 4 weeks later...

Just replaced the radiator with no change. Top hose is hot, all other hoses are cool, bottom, heater hoses and the radiator. Im thinking clog. Any suggestions on how to track this down, I'm just gonna start pulling this thing apart. I know its not the heads cause there was so much pressure in was blowing out the overflow and the top hose past the clamp.

Also the heater blow cool air

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was going to say if one hose feels hot and the other doesn't than the thermostat isn't opening, if your heat goes hot to cold sometimes than you have air in the system and need to open the air relief screw to bleed it out.

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  • 2 weeks later...

On the back of the intake plenum at the top is a small screw with a label that says DO NOT OPEN HOT!. When filling the cooling system, just remove the screw, add fluid to the radiator until it comes out the hole and reinstall the screw. That removes air from the system. I have come across a lot of bad t-stats out of the box. It is very common and with a good one, your engine should be running 190-210 F to keep the engine happy That comes out to about the middle of the temp gauge in the dash.

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its generally worth testing new/old thermostats in a old electic fry pan fill up with water and set to heat up to needed temp and with a temp probe and wait to see when /if opens then turn off and wait to see when it closes if its in spec all good if not try another till you get a good one.

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