I replaced radiator this summer it has a new waterpump too sometimes the temp fluxuates from 210 to 225 or so . The other morning it was cold so I let it warm up. I go back out and its blowing cool air until I drive it it gets warm. Today at stop light it goes cool and I take off again it blows warm again. Any Input? Tstat? Core? Thanks guys!

 

Vacuum/blend doors issues? Maybe when youre on the gas it creates enough vacuum to properly actuate the blend door?

 

could be clogged heater core, could be blend door problem, the more you're on the gas, the less vacum the motor will make, check your vaccum canister too sounds like maybe it inst storing the vacuum properly.

 

How do I check these

 

also make sure to check the coolant level. My Chevy trk does this when the
level drops.

 

Coolant level is fine

 

Also curious about this, I noticed the same thing today. But I think I am just a little low on coolant in my case.. Hopefully.

 

Heater blend door is cable operated so that's not it. If it were a vacuum issue all that would happen is the air would come out defrost and would still be hot.

Do you still have the factory heater valve in the heater hoses? It could be sticking closed.

 

No mine dont this summer I got rid of the factory closed system. Put in a open system with All new hoses.

 

The heater control valve has nothing to do with open or closed system. It was used on both. Did you eliminate it in the process of converting?

 

Yeah I plumbed it all straight

 

Sooooo do I need it or what? talk about leaving me hanging lol

 

You don't need it and that means something else is the cause.

 

Hard tellin

 

Still have the original type closed cooling system with the bottle on the passenger side firewall?