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Discussion Starter · #1 ·
Got a strange one here. Temp will get to and maintain 190 most of the time, but if I drive at about 70-80MPH consistently (2000-2500 RPM) for 10-20 minutes, the temperature will start creeping up. If I slow down or put it in neutral and rev it to 4000 rpm for a few seconds that seems to get some coolant flowing through the radiator or whatever is blocked up to get the temperature back down.

I've read the heater cores get plugged up so that's what I was going to look into next. I replaced the thermostat (what a job!) thinking it was getting stuck but the problem remains. Upon reassembly I discovered the oil cooler housing was leaking coolant and oil so that's been replaced as well. Changed the oil after replacing the housing and found lots of coolant in with the oil. I'm hoping that was just because of the vacuum/pressure testing I did discovering the leak in the housing and wasn't actually driving it with that much coolant in the oil. No issues holding a vacuum or 1.5psi pressure for 20 minutes with new housing in place.

So aside from draining the coolant again (maybe just clamping off the lines) and checking out the heater core, any other ideas? I know on other cars the heater core is typically bypassed with a valve until the heat is turned on but could a blocked heater core cause an issue like this? Does coolant always flow through the heater core? I did turn on the heat when the car was running at the pictured temperature and there was hot air coming out.

About the rest of the christmas tree on the dash- I have new ABS speed sensors to install today since I got electrical faults for both front wheel speed sensors...

Speedometer Trip computer Odometer Motor vehicle Tachometer
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Discussion Starter · #2 ·
I bypassed the heater core and it still overheats... Need ideas on what to check next. If the car is driven at about 70mph at a rather consistent RPM it will start to overheat after about 20 minutes. The trick to rev the engine will get the temp to come back down. Maybe it's some other contamination in the system blocking the flow, or one of the other coolers (charge air or transmission) blocked off?
 
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