Where do you have the temperature sensor located? Do you have a laser temperature gun to verify the coolant temperature as you change from heat to a/c and visa versa?
If its a mechanical gauge and it is fluctuating that fast I would definitely think its a gauge issue.
Which is what Foxtrot was saying or that's how I took it anyway,or air in the system
That is unusual. I thought it was immediate. It does seem like a flow issue where for some reason the heater control valve is going shut when you switch to cold and stopping the flow through the heater core. Not sure why that would happen unless its on max ac as was stated earlier and this shouldn't cause the temp to rise. Have you checked the coolant level also?The gauge only fluctuates when I switch from hot to cold. It gradually increases to about 220 after about 10 minutes. Within 30 seconds it goes back down to 195 when I switch it to hot.
And the gauge is in the intake by the thermostat. Only place for it.
Bout a year ago when I put the motor in. heater core is brand new, radiator is brand new, hoses are new. heater valve is new.When was the last time the complete cooling system was flushed?
It's been doing it since I put this motor in. When I ran with no heater core it was fine. I think the heater core is the issue, which is odd. Factory cores aren't aluminum, yet you can only buy aluminum cores nowadays. I think that may be my issue, it's letting too much heat build up in the box with everything off. Either that, or my heater valve is malfunctioning and letting coolant go through even when everything is off. The left hose (bigger of the two) will get hot regardless of what happens, and the hose with the heater valve will only get hot upto the heater valve. The routing is the same on the SBB as the 3.8, and I'm sure I have that correct. Larger hose (with the pre molded end, kind of hard to misplace it) goes to the nipple on the water pump, smaller hose with the inline valve goes to the pipe fitting on the intake.Did this just start or has it been like this?
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