So, I just got a mechanic to fix a coolant leak in my 93 XJ and now the heater is not going. It was pretty weak before but now even after 30 minutes of running it blows as cold as the cold setting. He reckons it is nothing to do with him but it was going the day I dropped it and now it is not going. My feeling is it is something to do with the thermostat though I don't really know that much.

Any ideas as to what he could have done to kill the heat? Thanks in advance!

Matt

 

What exactly did he repair?

 

Thats what im wondering.

First thought was a blocked heater core and/or the vacuum line to the heater control valve is broken.

 

If it barely worked before I would say the heater core was nearly plugged with gunk, or if Jeeps have a climate panel controlled heater coolant valve, that valve was about failed. It could be that his work shook loose more sludge and blocked the core, or he might have bumped something with the valve that made it fail/bind up/disconnect it's control signal.

Your service invoice should include some sort of description of what repair was performed, and what parts were used. If it doesn't I'd be looking for a different mechanic. If he did a hose related to the heater then the gunk thing is possible, and the disconnected valve is possible. If he did upper or lower radiator hose the gunk theory is more likely, etc... We could do this all day without knowing what he did.

 

Thanks, sorry for the lack of details.

Thing is, he is a "mechanic" in that he is local and repairs cars... my mistake. No receipt. The leak was near the radiator and he said he tightened a few seals (or whatever). I flushed the heater core two years ago and replaced the thermostat, which is when the heater started working. From what I worked out last time I had problems (via this forum) my issue was with the thermostat last time, like it had been jammed closed. I am willing to admit I know very little, but replacing the thermostat worked last time, hence why I thought it might be to do with that again. Sorry for the lack of knowledge and detail. No stress if you can't (or can't be bothered) answering any more. Heading into summer in NZ so no rush on a fix.

Cheers.

 

No need to apologize. No one I've ever met knows everything.

It's tricky to diagnose through the net, but that's what we're here to do. People who don't know can't reasonably be expected to pre-answer all the questions precisely because they don't know. Nothing wrong with that, we're all born without knowledge and don't have time to learn everything. That's why they are searching for help after all. So I think everything is proceeding apace and as expected. All good there.

I've done all my own work for about 20 years, but I still don't feel like an expert. I'm pretty sharp on 1995 Subarus and 1976 Volares. But I've only owned a Jeep for less than a month. When I post I'm always in the frame of mind of the 'straight man' from comedy. That is to say I'm hoping to get discussion moving in the right direction, expose various theories and methods, and hope for some additional people with skill and experience to add consensus and additional details.

I've heard of a stuck fully open thermostat causing weak heat in the cab because the full open thermostat is allowing the radiator to do too much cooling. But I don't think that would feel like zero heat inside the cab. I don't think tightening some clamps to reseal a small leak would do anything to gunk up the heater core. If the clamps in question were at the heater control valve that would allow for knocking loose a wire or vacuum control connection or overclamping the valve causing its internal mechanism to bind up. I suppose if the radiator end tanks are mode of plastic over tightening a clamp could break part of the internal part of that connection and the chunk of plastic could jamb the thermostat or block the passage to the heater. I over tightened such a clamp long ago and broke off a hoop of plastic from the connection. I had to replace the radiator after that.

 

i would look to see if the vacuum line going into the heater box was disconnected or broken. All those controls are controlled by vacuum.

 

What does your temp gauge read when fully warm? Do you have an infrared thermometer to check the temp at the thermostat housing? Also check the inlet and outlet to the heater core.

 

Thanks again guys! Right I will get out and have a look at all the connections around the heater core/box. I guess part of it is going through the various stages of diagnostic, checking to see if both pipes are hot, checking to see the various wires etc are all properly connected, making sure the engine is getting up to the right temp (have not driven far enough yet to check that, hopefully today). I will get back with any further findings, cheers!

 

one thing that might get overlooked is replacing the radiator cap. If your rad was full of gunk the cap should be replaced. They’re cheap, and are very important. Years ago mine was shot, and when I replaced it I noticed that my heater really started pumping out nice and toasty heat.

 

Cool thanks for that, will check it. Sounds like a potentially very easy fix.