No heat below 35 mph?

[Dboy11]

So as I was driving into work this morning I noticed that going down the highway the heater works awesome. Then, every time my speed drops below 35mph, it will start to blow cold air. Any ideas? Its not that cold yet but definetly need to figure this one out asap!

 

[12vriviera]

my guess is on highway ur vacuum pump at speed can over come leaks or a failing pump. Quick check with a vacuum gauge will confirm or deny that one..

 

[Dboy11]

Thank you sir! I will do check it this weekend. I do not like cold air when its cold!

 

[jwfrauts]

Have you checked the coolant in the Degas bottle? Mine done that when it was low on coolant. Anytime I slowed down it would blow freezing cold. Filled it up and never blew cold again.

 

[SINNER]

Vacuum pump is electric on 6.0's so do not even bother with that. Def. check the coolant level because as stated above when low it does exactly what you are talking about.

 

[Bustedknuckles]

You know 6.0s have problems with head gaskets blowing causing pressurization of the cooling system?oke:

 

[Dboy11]

Ok so i will check the degas bottle, I also do have one bad injector and am fixing that **** this weekend.

 

[Dboy11]

Have you checked the coolant in the Degas bottle? Mine done that when it was low on coolant. Anytime I slowed down it would blow freezing cold. Filled it up and never blew cold again.

That fixed it...Thank you !

 

[BC06PSD]

Water low or water pump is taking a dump. I think I read somewhere the impellors are notorious for breaking. Could be what's left of the impellor can only move the water at a higher rpm.