Heater blowing cold on the highway

[Steve6L]

Well recently it has been about -20 here and heater works great when my truck is idling or cruising around town. However I soon as I get on it on the highway and go say 70+ the heat goes away and I'm left with cold air. What could be causing this? A side note if I stop and rev it up my coolant temp drops from 190 to 172ish slowly however if I just stay on the highway it will stay up at 190...

Thanks for any help from a very cold Canadian after Driving 5 hours today.


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[Xcler8]

No idea but I feel you on the cold haha alberta is no Mexico.


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[Steve6L]

Anyone got anything here?


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[Tuscany]

Head gaskets. Is it puking coolant or are there any coolant leaks?

[Steve6L]

Bryan how could head gaskets cause a drop in interior temperature? And yes it pukes coolant, puked for about a year now. I just do not know how that would cause my temp to drop.

How about my bypass coolant filter being clogged? Could that cause any problems?


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[Tuscany]

If it has blown head gaskets it will push the coolant out of the degas bottle causing it to lower past the heater core (it sits HIGHER than the degas bottle and rest of the cooling system) so while there is enough coolant to continue circulating through the system and keep from overheating (for now) it will not reach the heater core and produce heat in the cab. That is the first indicator I used in my truck to diagnose blown head gaskets on mine last winter when they blew.

Either that or your EGR cooler is ruptured (if it's still intact, no description in your sig for an EGR delete).

[Steve6L]

Egr cooler was ruptured and deleted not to long ago. Poured 2L into degas bottle today hahah guess you were right, how long did you limp yours for? Where's the coolant going though doesn't look like its pouring out the degas bottle although it is pretty dirty


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[Tuscany]

It's getting pushed out of the degas bottle. May be a little at a time or a lot at a time and dries before you notice it. I drove mine like that (babied) for a few months however I don't recommend doing it as it can and will cause the head gasket to leak worse and worse over time. That will make it puke A LOT and can cause your truck to overheat. When that happens you significantly increase your risk of cracking the heads and costing yourself thousands more in repairs because you have to buy new heads then.

[Steve6L]

Ah I see so that pretty much guarantees that my head gaskets are gone. Well I can add rebuilding motor to the ever long list of things to do, including swap out rear diff, new tranny and coil over front swap


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[Tuscany]

LOL I would worry about the engine and trans first!