Skip the auto shop - Our mechanics make house calls

Q: New thermostat and truck is still blowing only warm air. It blows cold air when idling

asked by on

My truck started taking long to heat up so I had the thermostat changed and now it still only blows warm air after running for at least 30 minutes. When I sit at red lights the truck blows cool air

My car has 179000 miles.
My car has an automatic transmission.

A: Trapped air in the cooling system can somet...

Trapped air in the cooling system can sometimes account for this but you are indicating that you are getting heat, at times, which would indicate that coolant is flowing. There is a heater control valve and you want to make sure that the valve is fully open. If it is not fully open, delivery of heated engine coolant to the heater core will be much reduced. Once you have confirmed that the heater control valve is fully open, check the temperature of the heater hoses leading to the valve. The hoses should be hot, just like the radiator hoses. If the valve is open, the hoses are hot and the heat is still inadequate in the passenger compartment, that means the blend door in the dash is stuck in the wrong position, not allowing air flow over the heater core, and/or the heater core itself is plugged and thus not allowing adequate circulation of hot engine coolant. If you desire that a certified Mechanic from YourMechanic diagnose and fix your no heat condition please contact YourMechanic to set up a mobile visit.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: battery voltage drops dead....

The wire hanging may be an engine ground. Check the wire to see if it is black and see if it is broken or has a large eyelet where it should be connected somewhere. If it is the main ground...

Q: Heater blower stopped putting out heat.

If the blower doesn't work at all (i.e. it doesn’t blow warm OR cool air) then the problem is likely with the blower motor or its circuit. Blower motor control can be complex on late model vehicles, especially European ones,...

Q: Car not starting

Based on your description it is most likely the starter. However I would not eliminate the battery without fully testing it. I would recommend hiring a qualified mechanic to test your battery for proper voltage and charging. I would also...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.