2006 XC70 Heats up then cools down at stop lights

[IVIUSTANG]

Hi Guys,

Last winter I had the fun of slow coolant heatup, so I replaced the thermostat and coolant. Also in the summer I did a complete timing belt job including water pump.

However I am still having the same symptoms as last year, at -15C or colder the car warms up really slow, and once it finally is up to operating temperature; at stop lights or when idling the temperature gauge will actually dip down a few lines. When it is -25C like tonight the temperature gauge goes to around 1/4(when halfway is normal) when my car is idling. I can't handle this, it will get to -40C and I need this car to be a heating machine!!!

My previous Volvo(1998 S70 T5) heated up MUCH faster than my XC70 and it didn't have the temperature drop.

Anyone have any ideas other than thermostat or coolant?

Thanks,
Jesse

[JRL]

Either it was a bad thermostat or a coolant temp sensor but that usually throws a code

[sjonnie]

Anyone have any ideas other than thermostat or coolant?
How about your fan? Is that coming on when it shouldn't? Could be a problem with the relay or your temp sensor as JRL suggested.

[IVIUSTANG]

Fan is operating normally, and no codes according to Dice. I really don't want to believe this is the thermostat since I just replaced that with the Volvo part and I wasn't a huge fan of the job. Anything else it could possibly be before I put another $100 thermostat in this beast? My car has the identical symptoms before and after the new thermostat and coolant; I troubleshoot electronics for a living and in my line of work I would attempt to find another reason once the most probable is ruled out.

Thanks,
Jesse

[vtl]

Check hose temperature with bare hand, should be cold when thermostat is supposed to be closed.

I had to change mine twice: first one was microdamaged, even saw steam escaping t-stat assembly.

[hoonk]

Buy an infrared thermometer - ($15-$200) You will then be able to compare what Vida says the coolant temp is, what the gauge indicates and the actual coolant temperature - (can check heater output temp also - I imagine that would be important at -40!) A new temp sensor comes with the thermostat assembly, and that part number has not been a common replacement. (so I would not expect 2 sensors to be bad) The sensor used in the earlier cars did commonly fail, as well as the thermostats would not close all the way. That would usually set a temp sensor code because it took too long for the car to warm up.
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