I have a 1989 Wagoneer Limited. It has never had adequate heat inside during the winter. I removed the mixing valve in the engine compartment because the plastic portion of it broke from old age, and I thought that might improve the interior heat. It didn’t seem to help. In spite of a lack of heat, the engine temp gauge is always acceptable (if not too high). Any suggestions?

 

Are both your heater hoses equally hot? If not, the heater core isn't flowing enough coolant, plugged in other words. If they are you should check the temp mixing door in the heater to make sure it's not bypassing cold air from the A/C evaporator.

 

Even with the heater core bypass valve removed, you still get a some coolant bypassing the heater core by going through the bottle instead. The bypass valve actually contributes to the heater core sludging up. Best upgrade I ever did on my 1989 was replacing the radiator with the open style (from a 92 as I recall), flushing the heater core back-n-forth until it ran clean, eliminating that crumbly plastic bypass valve, and the failure prone surge tank. I put on overflow bottle where the surge tank used to be. Engine ran cool again, and tons of heat when I want it. Many will swear the oem closed style is just fine, but since I was replacing the radiator anyway, I chose to upgrade to the newer setup.

I had that stupid surge tank split open on the highway when it was -10*F. The steam cloud was impressive enough, I could barely see to pull over, and people were stopping thinking it was on fire!

 

I will check this. I have considered doing what lawsoncl suggested - I heard somewhere of someone doing that. If I do that, I will end up flushing the heater core anyway, so that would be a pretty comprehensive approach.

 

I have had that surge tank split, or the cap split, before too, and I don’t understand why they designed it that way. Terrible idea. Replacing the whole radiator and adding an overflow reservoir seems like the best approach. I would also end up flushing the heater core, as dave1123 also suggested. I have had engine overheating problems as well, due to the lousy closed cooling system. I am considering selling the Jeep anyway, so maybe I can get this taken care of first. Many thanks for your perspective.

 

The aftermarket caps surge tanks are really poor quality. I had lots of trouble getting the cap to hold pressure, and a number of boil overs as a result of the cap jumping threads and getting loose. Supposedly a cap meant for a Volvo something is much better quality.

 

I read a post by someone about putting a hose clamp around the cap to prevent it from jumping threads. I did that as a last resort, and it seems to have worked. Of course by doing that, I am not sure what kind of pressure would have to build up in the system before it got relieved at a reasonable level, since there is no pressure relief cap on the radiator. Are there any other ways the pressure can be relieved, besides the cap and surge tank? Perhaps a burst disk in the radiator?

 

There is actually a spring in the surge tank cap that should relief at 16-psi. I never could get it to hold more than 10-psi without leaking. You could also eliminate the surge tank and replace it with something like this, but you'd probably be better off just putting that money towards a new radiator, especially if it's original.

 

Think about the time. The XJ was designed largely by Renault and used what they were using at that time, ie, closed cooling system and the Renix injection system. Sorry to say, at that time, the French were not known to build quality automobiles. Peugot was the exception.

 

I think replacing the radiator and tank with a conventional system is the way to go, along with flushing the heater core. Takes care of the heating problem and the engine overheating issue.

 

Ah that explains it. Poorly designed system.