1999 Cherokee Sport 4x4; 5-spd; 4.0L - so now in the past two weeks my Jeepster's heater has decided to

1. only produce mildly warm rather than hot-at-the-top-of-the-dial as it used to, and
2. fog up my windshield when I'm running heat-to-my-feet ... when I change to defrost, the windshield clears up nicely, but ...

Any suggestions how to go about whupping this thing back into shape?

Many thanks! Appreciated.

 

So you are saying your vehicle is almost out of coolant & you need a heater core?

 

Umm... coolant is in fine condition (had new radiator installed last week); don't know about the core business; time to talk further with my mechanic?

 

The heater core is like a mini radiator inside the dash,Its where the heat comes from so if its clogged up you will have no to little heat.See if they can flush it a few times if that don't help you gotta replace it and i think you gotta pull the whole dash to get to it.

 

Try a back flush. My heater never work properly even after changing the radiator ,water pump thermostat ect and giving the whole thing a realy good flush. Did a back flush on the heater core and I was amazed at what came out of the thing. Even though my coolant was like brand new, a heap of brown crap came out of my heater core when I ran a hose through it backwards. Heater works like a new one ever since.

 

This telling you what your problem is. You have a leak in the heater core. No amount of flushing will help. Matter of fact it may cause it to leak even more by clearing the crud out or even just by making the leak larger.