Not warming up
 

So my car seams to be not warming up properly. When the car is at idle it will warm up to normal temperature but when start to drive then the temp starts to fall. I'm not to sure what could be the problem I replaced the thermostat with a fail-safe about 2 months ago.

A defective T-stat/coolant temp sensor. The OEM is Vernet (French)/Wahler (German). Or, if the ambient temp is overwhelmingly cold, you could cover the front of the A/C condenser with a sheet of cardboard/aluminium to block ram air.

JPN

Well I'm in 10 degree weather and I'm not having any ambient temperature problems so it's unlikely someone in Sacramento would.
It sounds like the thermostat might be at fault if it's opening too much and allowing too much water to circulate. Once you start driving you're spinning the water pump faster so you're moving more water and the speed moves more air through the radiator dropping the temperature and the thermostat should close some to hold the temperature steady.
It's a pretty tested rule of thumb that an 850 at it's proper temperature will sit at about 3 O clock on it's dial. It might rise a little and drop just a little but it should move either way much.

You might want to try a different thermostat or just to find out what you're really at, tape a thermometer to the upper hose and see what the actual temperature is at idle and with the engine held at 2K or 2.5K rpm.

Do you notice any bubbling in the reservoir tank ?? Any loss of coolant ??

well i pulled out my thermostat and it was stuck closed so now with a new one the car runs like its supposed to.

Thanks for the help everyone.

Must have been stuck open, if it were stuck closed the car would have overheated.

@RSPI, when is it a good time to replace your thermostat? is it part of the maintenance thing that needs replacing?

my bad i meant stuck open it was stuck closed last month lol

This is a design feature of the Motorad so-called "Fail-Safe" thermostat. In theory if the thermostat sees a coolant overtemperature it locks open. The problem is that that temperature will often be reached in a properly functioning cooling system.

This is a completely ill-conceived and pointless design, in my opinion. It is not "fail-safe", it is "guaranteed to fail."

so that would explain why it got stuck open about a month after i replaced it

What thermostat is this, and where is it located?

My car has the same problem.

It's the thermostat and gasket at the end of the upper radiator hose.

How to:
http://www.matthewsvolvosite.com/rep...0-or-xc70.html

its the coolant thermostat
its really easy to get to.
it only has 2 torx screws holding it down just make sure you dont round the torx out cause that will make the job a lot longer.
if you follow the little line from the coolant over flow tank down to were it hooks up to the metal, the upper radiator hose also is conected to that, the thermostat will be rite under it.