90 runner 3.0

Has been recently flushed. In cold weather, the engine warms up with 2 minutes of driving, and overdrive becomes available quickly. Even when driving in very cold weather, I never lose overdrive, so the engine is holding it's temp.

The rear heater blows hot within two minutes of driving.

The front heater never seems to get hot. It barely gets warm.

The temperature lever linkages are all good. The jumble of linkages under the ashtray works smoothly. The cable to the valve on the heater hose at the firewall is attached and actuating the valve. (the one with the funny grid on top. What is the purpose of that grid-cover?)

I'm thinking it has to be a blockage in or near the heater core.

But before I start pulling stuff, I wanted to ask if there is any other "recognized issue" that causes this?

If so, what is it?

If not, where is the heater core and do you have any tips for chasing this problem down. Y'know - like "drain only this first", or "only pull this and this and this to get to the core", or "use this test to see if the blockage is here". Y'know, that kind of stuff.

Thanks for your help!

 

I would disconect the line going into and out of your heater core at the firewall. Then take a hose and spray into one of the ends full blast, this will hopefully unclog your core if that is indeed your problem

 

x2, but make sure you put the hose in the return line. You want the spray of water going the opposite flow so it breaks up any clogs easily.

 

Thanks guys, I'll give this a shot.

 

Could also just be air trapped somewhere in or out of the front heater core. If so, get the air out and heat will return. It happened to me once.

 

mtgoat - How did you fix it?

General burp of cooling system, or specifically a part of heating system?

Thx.

 

Actually I drained the whole radiator and refilled it again slowly and the problem went away. I assume it was trapped air causing the lack of flow through the heater core. Of course follow all the basic tips for burping, ie...lift front end, squeeze the hoses, fill slowly...etc. I also take it one step further and disconnect one of the highest hoses in the system, in my case its the hose that runs coolant through the throttle body.

 

"The cable to the valve on the heater hose at the firewall is attached and actuating the valve"

Maybe the valve is not actually opening?

 

x2 with MtGoat.

I would start by burping the system with the front end up on ramps or an incline. It sounds like air in the system to me, too.