07 duramax classic 2500 not heating up the cab like it use to

[ippielb]

This is false. If one hose is hot, and the other is not, then the coolant is NOT circulating properly. The heater box doesn't remove enough heat for you to feel a difference in the hose temps. Both hoses should be too hot to touch. If one is untouchable, and the other, you can hold your hand on, the core is plugged. Flush them separately from a full system flush. They need to be flushed by themselves. Garden hose works great. Back and forth multiple times.

Dawn dish soap, any kind of non foaming dish soap works good for cleaning cooling systems. Got that trick from a mechanic at CAT.