Vehicle has 137,000 miles . Just bought it. I have determined that its neither the blender door or re-circ door using the information at the Heater Treater site.
I have never experienced a blocked heater core before in any of my vehicles. I get warm air. Not hot enough to heat the vehicle on a cold day.
A/c works fine.
So I don't know where to go from here. Suggestions on what it might be anybody?
Thanks.

 

I had the same problem with my 96ZJ. I disconnected both the inlet and outlet of the heater and flushed it with pressurized water. I was surprised what was coming out from it. Since then it's working fine. Also it's possible that air is stuck in yours.

 

Both of those things have occurred to me. I discounted the dirty heater core because of the statistically low miles. Don't know if that is valid or not.
It is more likely the air in the system as the top rad hose had been changed recently, right before I bought it. To do that they would either partially or totally drain the cooling system potentially letting air in.
I have had this problem on other vehicles and the system "burped" its self overnight on its own. If it doesn't do it on its own, then I don't know how its done.

 

You have enough coolant in the system?

 

Plenty of coolant. I whish it was that simple.

 

Make sure the hose from the thermostat housing goes to the BOTTOM inlet pipe on the heater core. That way the core will bleed it's air out by itself.

Another time is what kind of water was the coolant mixed with. My ZJ had this problem and my heater core was full of lime deposits because I used my well water to mix the coolant. I had to run the engine for about an hour with CRL in it to flush out the whole system and I couldn't believe all the junk that came out. Ever since then, I buy premix.

 

It does. The 4.7 in the WJ’s have a bleeder plug at the highest point of the cooling system. You remove this plug and add the coolant until it reached that point. It kind of minimizes the chance of having air trapped in the system. My experience is that vehicles will purge themselves anyway over time.

And that’s one of the unknowns of buy a used vehicle. You don’t know what kind of maintenance it had prior. I don’t know what kind of water or which type of fluid. I have thought of flushing the core either manually or with a cleaner like CLR.

Thanks

 

From what I've been told, Mopar switched from green ethylene glycol to GO5 with hoat in 2003, so anything before that should have the green stuff in it. However, GO5 was designed for aluminum systems and the 4.7 has aluminum heads. In other words, use what ever you want, just don't mix them.