If someone could please tell me what to try next, I would really appreciate it. I have a 1988 S10 Blazer 4WD 4.3. I have no heat and I have tried the following: New tsat, flushed the heater core twice, the blend door is moving, unclear how much. The inlet hose to the core is warm but the outlet return to the radiator is cold. The mystery is that water flows thru the heater core very easily. I can pour water in one hose and it comes right out the other. There no leak or smell of coolant. Can anyone help? Thanks.

 

Sounds like you need a new core. It is possible that it is flowing only through one part of the core and then right back out. If the whole core does not get the hot coolant, then it cannot transfer much heat to the air passing over it.

 

The gauge on the dash shows its up to temp right? Changing out the heater core really isn't that hard.

 

Yes the temp seems up to normal. I thought it could be the core but the weird thing is how easily coolant flows thru. Logically you would think that the temp of the hoses wouldn't be that different. OK can you hook me up with the details of changing the core? The Haynes manual is a little short on details. Thanks.

 

Click on the link in the post above.

 

Thanks. That's great info.

 

New info! I was wrong about the temp on the inlet hose. It was only warm from the ambient heat of the engine. At the core connection it is not warm at all. Somehow the engine is not supplying hot water to the pipe that supplies the heater core. How many places can that be clogged? Maybe the 90 coming out of the manifold is clogged?

 

Ya check the outlet. Maybe find a flush tool locally and try to flush the system, or get it flushed.

 

That is different. I would replace both heater hoses and while they are off, run a wire or pipe cleaner down through both fittings.

 

Thanks. I'm going to take out the rear fitting to inspect and clean and then flush the engine. What could be wrong with the hoses? They seem clear.