Having problems with your 1990 Subaru Legacy ?

Overheating radiator without leakage - 1990 Subaru Legacy

Posted / edited by AnonymousUser on : 15-04-2019

Answers :

I posted this in a different web sight I hope it helps.


Re: Overheating and blowing cold air
I have been a mechanic for 20 years. Your problem is the heater core is\015\012plugged. The cold water from the radiator blows directly at the\015\012thermostat keeping it closed even when you are overheating! BAD\015\012DESIGN!! If you look at the water flow charts in AllData you will\015\012understand. If you rev the motor to 3,000 rpm's the turbulent HOT water\015\012at the water pump impeller (near the thermostat) will reach the\015\012thermostat to open it and the car's temp will fall very fast to the\015\012correct temperature. If you remove the thermostat it will not overheat\015\012but will run way to cold. If you bypass (loop) the heater core it will\015\012not over heat.
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The hot water that leaves the heater core returns to the engine at\015\012the thermostat. It is the only hot water introduced to the thermostat\015\012to keep it open and allow the water to flow from and to the radiator. I\015\012normally just back wash the heater core and get large chunks of rust\015\012flake out then its fixed. Back wash then froward wash repeatedly many\015\012times. Also flush out the motor so you don't re plug the heater core. I\015\012hope you have now blown the head gaskets or cracked a head yet. Make\015\012sure to run the proper coolant in the car so you don't promote more\015\012rust flakes. And bleed the air out as mentioned in detail by other\015\012posters.
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Nobody knows this little secret. Not even Subaru mechanics at the\015\012dealer, no TSB (Technical Service Bulletins a special note after the\015\012fact to mechanics). After days and days of trouble shooting a 1993\015\012Subaru Impreza (2.0?) I looked at the water flow chart and then it was\015\012clear what was happening. This phantom overheating problem stumps the\015\012best mechanics and sends many Subarus to the crusher.
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\015\012http://www.subaruoutback.org/forums/...threadid=17264
Are the cooling fans coming on? To test fan circuit turn ac on, fans should come on. If they do, than it could be the temp sensor for the fans. If not than check fan fuses.
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