1990 Volvo 240DL. After 10 minutes of driving the temp. gauge doesn’t go up and there is no heat coming from the vents what so ever. I have also noticed that I get horrible gas mileage. What could cause this problem?
Are you in a really cold state? If the thermostat is stuck open and the temps are really low, it’s possible for the engine to never warm up, which would cause exactly what you’re describing.
Of course the other possibility is that you’ve lost all your coolant – so first step is to check the radiator and reserve bottle BEFORE your next drive.
Check the coolant level. Without coolant there’s no heat.
If the coolant level is fine, then I agree, the thermostat may be defective.
You may have a defective thermostat that’s stuck OPEN, making the car run very cool, and virtually letting no hot fluid through the heater hoses.
Get a good shop to test it, since this may be the root cause. Your air door of the heater system may also be stuck inthe Vent or A/C position. Have that checked as well.
The radiator is full and so is the reserve bottle.