Heaters blowing hot when still but blowing cold when moving. What could cause this?

ANGELRAE

MEMBER
2002 VAUXHALL ASTRA
12,700 MILES

Ive got air out the system, and the hoses are hot. Someone said theres air getting in the engine which will cause my head gasket to go and it will need skimming, is this right?

Monday, March 26th, 2012 AT 9:31 PM

1 Reply

DRCRANKNWRENCH

MECHANIC
3,380 POSTS

Not understanding the statement. You will usually have over-heating issues with a head gasket leak.
You are having signs of a bad thermostat that is stuck on open and cools the engine too much when in motion and can only get hot enough for the heater at idle.
Antoher issue is that the fan may not be coming on. Replace the thermostat first and see if that solves the problem.
Some newer cars with aluminum engines just have heaters that don't always stay hot. They just dopn't hold heat very well.
If you have a temperature gauge just keep an eye on it. If it continues you might be able to play with the heater core valve wchich allows more or less coolant into the heater core as you adjust the heat setting. It may be a cable or electric. You will see it on one of the heater hoses at the firewall.