No heat at idle.

[08_6.4stroker]

Hey guys my 6.4 has been having this problem lately when I'm driving I have heat but when I slow down and the rpms drop below 1000 I don't have heat. Egr is deleted, It's not loosing any coolant, it has only puked once after I filled the reservoir too full. I have done a pressure test and it gets up to 16 psi and stays there even at max boost. I'm kinda thinking it's head gaskets but I'm not sure. I can see bubbles come up in the degas bottle when I start it when it's cold but I don't see any when it's up to temp. Truck is an 08 job 1 with 130k.
Thanks for the help!

 

[Stroked777]

Have you drained te cooling systems recently or added any stop leak to it? Does the truck get to operating temp

 

[08_6.4stroker]

I haven't drained the coolant since I did the egr delete which was two years ago. And I haven't added any stop leak to it. It gets to operating temp. When I have the block heater plugged in and I start it in the mornings it blows warmish air but once I drive it it goes cold. Would the heater core be plugged?

 

[Stroked777]

If it was plugged you wouldn't have much heat at all I would think. Could be a blockage in a line

 

[greasltn]

You might want to check the water pump. I've seen a couple where the impeller slips on the shaft and will not circulate the coolant at low RPM.

 

[08_6.4stroker]

I suppose it could be the water pump I might take it apart and have a look.

 

[Stroked777]

You might want to check the water pump. I've seen a couple where the impeller slips on the shaft and will not circulate the coolant at low RPM.

I was gunna say maybe a broken impeller blade but I can't remember if they are plastic or metal

 

[greasltn]

lmpeller is plastic.

 

[Stroked777]

lmpeller is plastic.

So a broken blade Is a possibility,

 

[greasltn]

A broken blade is possible, but most likely impeller is just free spinning.

 

[Gary]

I'd try chemically cleaning the heater core, I do it often on all makes of vehicles. I have been using CLR with good luck, I'm gonna try VC9 on the next one.
Just remove the heat hoses from the engine, then flush with a garden hose both ways, then I blow the water out, add the cleaner let it sit for a hour, flush with the garden hose, put the hoses back on and your done.
I've done this on 100's of vehicles over the years and don't ever remember it NOT working, 6.0's and GM dex-cool vehicles are the most popular, I wrench for a living.

 

[08_6.4stroker]

Well pump doesn't have a broken blade and doesn't look like the impeller has slipped. I'll be replacing it regardless along with new thermostats and see what happens.

 

[08_6.4stroker]

Gonna bump this up. I have supplemental heat so my truck starts heating pretty much right away. Now once the coolant gets to about 160 degrees all heat goes away until the thermostat opens at 203 degrees. Now after that the coolant stays right at 190 and I have heat. Until I shut the truck off and the coolant temp gets below 160 then it goes back up to 203 I get heat and it drops to 190. I've already replaced the thermostats for a second time. I've also replaced the rad since it was leaking. Not sure what the problem could be.

 

[DarkSide2.6]

I know you have a 6.4 but I had a 6.0L with no heat at idle and poor heat driving, put in a new thermostat and that fixed it.

 

[webb06]

Gonna bump this up. I have supplemental heat so my truck starts heating pretty much right away. Now once the coolant gets to about 160 degrees all heat goes away until the thermostat opens at 203 degrees. Now after that the coolant stays right at 190 and I have heat. Until I shut the truck off and the coolant temp gets below 160 then it goes back up to 203 I get heat and it drops to 190. I've already replaced the thermostats for a second time. I've also replaced the rad since it was leaking. Not sure what the problem could be.

Is the coolant getting pressurized?

 

[08_6.4stroker]

I have already put two sets of thermostats in. And yes the coolant does get pressurized.

 

[webb06]

I have already put two sets of thermostats in. And yes the coolant does get pressurized.

I would put a gauge on the bottle and see how much pressure there is. Are the egr coolers still on?

 

[08_6.4stroker]

I would put a gauge on the bottle and see how much pressure there is. Are the egr coolers still on?

Egr coolers are off. And I did put a guage on it and it was right at 16 psi no matter how high I got the boost.

 

[webb06]

Egr coolers are off. And I did put a guage on it and it was right at 16 psi no matter how high I got the boost.

16 is too high for normal. The cap is probably popping off. I would take a guess you have a blown head gasket.

 

[08_6.4stroker]

16 is too high for normal. The cap is probably popping off. I would take a guess you have a blown head gasket.

Well I guess that's possible. I just don't understand why it consistently stops at 160 degrees. But wouldn't it take more boost then 15psi to get exhaust gas into the coolant system to cause a vapor lock? It stops heating while cruising down the road with boost below 15. But when it is heating and I bring boost up past 40 it stays heating.