Hi,
For a few months I thought the temp guage on my 1990 740 wagon was sticky. If I tapped the dash, sometimes it would show OK.
But, now that winter is here, no amount of tapping shows any engine temp. Plus I can get a tiny bit of heat, but not enough to stay warm, plus it hit me the other day when I was driving and could see the exhaust in my rear view mirror, even though the engine had been on some time.

I think it's simply running cold. How likely is it that the thermostat is stuck open?

Everything else runs fine. I'm out of town right now, and can't check if the heater hoses build pressure. (didn't want to drive for hours if the engine wasn't heating up)

Thanks.

Hi
I don't know where you are or your outside temperatures, but I live in Thunder Bay Ontario. With serious winter, although the coldest this year has been -25C.

I had the same symptoms as you described; changing the thermostat did the trick -and now i have toasty warm heat. Volvo themostats are designed with the default setting on failure as "open". That's why you only get a little heat, and you don't get overheating.
The replacement volvo thermostat is relatively expensive: about C$25, compared to about C$10 for a generic thermostat to fit GM/Ford etc.

Good luck
Duncantee

can also be a very low temp thermostat; make sure the cooling system will hold pressure before putting in a hotter one.
--
Stef (81 245 B21A SU M46 3.91 330000km, 81 244 BW55 3.31 220000km)

It's very likely. We've had to replace the thermostat on our 91 Volvo 740 twice, and I'm due to do it again. Every time the part gets replaced, the issue gets fixed.

A temporary solution would be to cover the front of the radiator with a thin piece of plastic (think rubbermaid tub lids) that covers about 3/4 of the grille intake. This will lessen the amount of cold air that runs through the engine, and will thus reduce the efficiency of the heat exchange that the vehicle is getting.

I've been doing this for the winter until I have the time to actually order and replace the thermostat itself. It's been working great.

Do not check on the thermostat until you have a new one to install. Get a Volvo brand, they are not expensive and hold up very well.

Labor to check the t-stat is the same as to install a new one. If the old one is good, you have a good spare.

Goos Luck,

Bob

:>)


PS You have topped up the coolant, right? Coolant so low that it doesn't reach the temp sender won't send any temp to the gauge.