Hi Guys:
The needle on the temperature gauge on my 87 740 took forever to reach the middle (normal) this morning. After idling the car for 10 min or so
every morning,the temperature usually reaches normal level by the time I take off even in the middle of the winter. This morning after that time the needle was just half way to the middle of the gauge. And only after driving about
20 miles the gauge was showing normal (or close to it) .
What is causing this? Electrical problem with the gauge,temperature sensor,
thermostat... Any ideas? Where/what should I look for?
Tks


PS Now not only the needle takes forever to reach normal level,but it drops
from there as I drive along,to go back to normal. If I turn engine off with needle at normal temperature and turn the ignition back on,needle goes
immediatly to normal...
Can anybody give me a hint?
Tks

I had the same problem on my '91 740 a couple of years ago. Sounds like your thermostat is broken. With a broken thermostat, it is always open, so engine is very slow to warm up; also, falling coolant temperature as you drive since more airflow through the radiator results in lower temp. coolant leaving the radiator. I am on my third or fourth thermostat--I have stopped counting.... just another routine maintenance step for me.

If your temperature gage acts erratically, your temperature sending unit is probably wearing out--it is a temperature-sensitive resistor. You can test by placing a 100 ohm resistor (from Radio Shack) between the leads of the wire going to the sending unit. When this is done, the gage should read normal. The sending unit is a bit tough to reach, but you can get to it to replace it. My bet, however, is a broken thermostat.

Good luck,
Jim Nau
'91 740 130k

Where is the temperature sending unit located?

Is it the same (blue or black) one under intake #3 which signals to the EFI?
--
'Can't understand why people abort Volvos, either'

Tks Jim. I'm gonna replace the thermostat and see if I solve the problem!

How old is your thermostat? Sounds like its sticking open.

My thermostat is at least 5 years old. I 'm gonna replace it and see if problem disappears. tks guys