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RWD - Odd Overheating Issue + Remedies

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Odd Overheating Issue + Remedies 900 1993

Hello everyone, I recently diagnosed a very strange overheating issue with my car. I thought some of this information may be useful to some.

Basic information about the car:
1993 Volvo 940 Turbo Wagon (B230FT)
Motor had a budget rebuild that entailed the following:
All new seals on bottom and top end of the motor
New connecting rod bearings
New Rings
Turbo Rebuilt
Valves Re-Shimmed (Was causing loss of compression)


Issue #1: Violent overheating that caused coolant to spray out of the cap, happened extremely quickly.

Remedy #1: I had filled the system too quickly which caused air to become trapped in the block. To fix this i removed the thermostat, drained the coolant and filled it from the upper radiator hose very slowly until it started coming out of the radiator itself. I then reattached the upper hose, filled the system to within limits and squeezed the upper radiator hose to help move some of the air to the expansion tank. I then ran the car without the thermostat until it indicated around the normal operating temperature. I let the car sit overnight as recommended by some forum users. This fixed the "explosive" overheating issue that I was having.


Issue #2: Coolant levels rising slowly and pouring out of expansion tank, was not explosive but happened rather quickly.

Remedy #2: This is all done without the thermostat in the car. I had a thermocouple that hooked to my multimeter that i taped to the outlet of the thermostat housing. This was reading about 165-170 degrees F before it would pour out. I narrowed this down by trial and error to the system not being able to pressurize due to a faulty expansion tank cap. This allowed the system to not overflow and would stay self contained up to 190 (above limits).


Issue #3: Car getting unreasonable hot at idle, temps stayed between 180-190 degrees with no thermostat and the fan running on low setting.

Remedy #3: The car had a high idle which i adjusted down to about 1000 rpm, not too much out of tolerance so I let it be and figured i would set that after the overheating issue was resolved. Turns out that the point where the break booster connects to the intake manifold had broken off and was causing a massive intake leak that was not visible until closer inspection. This caused the car to run extremely lean and generate a mass amount of heat. Once i fixed this issue the car ran much better and the temperature stayed around 130-135 degrees F. I put the thermostat back in and had no more issues. If you have this exact issue make sure that you check every point in which an intake leak could occur.

Hope somebody finds this useful, although it seems so simple I ignored the small signs of a huge issue and completely focused on the cooling system itself.

 





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New Odd Overheating Issue + Remedies [900][1993]
posted by  B230FTENTHB  on Thu Oct 25 20:32 CST 2018 >

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