So here's the conundrum. Can't get heat out of the ac system. Have replaced front heater core and thermostat. Flushed system. Checked control cables and doors in the heater itself. Incoming heater hose into core is hot. Outgoing is only warm. I can get some heat but only if I Rev the engine over 3000rpms. Ideas?

 

Some info about year, engine, model, etc. would be helpful.

What do you mean by "front heater core"?

 

He's probably got a 4runner. There is a separate heater core for the rear. I don't know if it helps but I've got the same situation. I live in a desert though so I haven't bothered with it. Curious to see what you figure out.

If you've got a 4runner does the rear heater get hot?

 

When you say replaced the heater core??

You are talking a brand new one??

For what ever reason you have no flow through the core blockage in the core or while the valve appears to be working it is not.

air pocket or coolant level to low

pretty much all it can be.

 

Being I have a Tacoma, I tend to forget about the two cores in the 4Runner.

 

Yes. 97 toyota 4 runner 6 cylinder 2wd. Replaced front core with a brand new one. The rear core is slightly warmer but not by much. Water can easily flow through. Tried "burping" the car but didnt help. Any suggestions for doing this more succesfully?

 

What temp t-stat do you have in there?

As Wyo mentioned, is the heater valve under the hood working properly?

 

Your not trying to get heat with the AC turned on??

I have seen it tried before.

You need coolant flow through the heater core something is keeping that from being able to happen !!!

Does this have a manual cable operated valve or is it a vacuum or electric valve.

Dumb question How long are you driving vehicle to get it up to temperature ??

The Thermostat needs to open to get heat.

It might be possible your radiator or water pump is on the way out just a guess.

What pressure radiator cap and is it good ??

My 4Runner 3.4 takes about 4 miles no matter how long it idles I don`t get much heat.

The 2000 Tacoma is hot in a few minutes of idling .

 

OP, what is the air temp outside when you are trying to get heat?