'90 240 wagon.
I just changed the thermostat the other day and now the gage is all over the place.
When I'm doing in town driving, stopped in traffic and not going over 40 the temp reading is fine. Half way up where it should be. But when I'm out on the highway doing 70 80 mph. the reading is almost in the red.
Any ideas what this might be? Some type of vapor lock? Bad water pump? bad thermostat?
Any ideas?
Thanks
Andrew

are you sure it is not the temp gauge it's self, dose that year have the temp conpinsator circut board that Volvo started installing to snub out rapid fluxations?

Well, it may be that there is an air pocket in the system. The thermostat needs to be installed with the little air venting mechanism pointing "up." See the pix in the 700/900 FAQs (they had the same engines as the 200s) at:

http://www.brickboard.com/FAQ/700-900/Cooling.htm#Thermostat_Replacements

So, I'd reinstall the thermostat, make sure that the venting nipple is pointed upward, top off with coolant, and then run the car up to operating temp with the coolant recovery cap off. Watch for the coolant level to go down some after reaching operating temp. Top off again and it should be OK.

Hope this solves the problem.

Mike
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Mike Brown Greenville, NC 1996 965 105K 1994 940 135K 1986 244 137K

I'd vote for the bad thermostat, if this just started suddenly when you installed it. Either that or you put it in wrong....