740 Heater Low temp air

1990 740 Turbo. Good fluid antifreeze/water mix level in the radiator
"tank" . The temp sensor is about 11:00 (close to cold) compared with the
12:30 (just over half WA) it normally is and the air temp from all the vents
is lower than it was a few weeks ago. We have a cold spell here in WA, it's
been in to 20 most nights. Maybe the thermostat is stuck OPEN?

 

It sounds to me like a perfect thermostat failure. If your interior heat
had been normal, one could have suspected the temp guage or sensor. In
your case, replace the thermostat.

It is a very easy job to replace it. Max 1 hour if you drain some of the
coolant and refill. 10 minutes if you let coolant spill and replace. Not
so environmentally sound though.

After replacing, keep an eye on coolant level for the first days, it
often takes a while to get all air out, and the level goes down a bit.

Good luck!

--
Gunnar

240 Turbo Wagon '84 200 K Miles
940 Wagon '92 150 K Miles
on Swedish roads