91 YJ Heater problem

Your radiator is low on coolant. You need to use a mix to top it up. You are pretty safe with the same color I think. Top up the rad first, then top up the overflow to be sure the rad still doesn't have air inside.

You are describing low coolant in the rad with the temp changes.

Mike

A low coolant level will almost always result in poor or no heat output.

If you have American Green then you can, most likely just top it off with a

What color coolant do you have?

your core could be clogged. unhook both hoses going to the heater core, at the engine side, and stick a garden hose on the side where the coolent flows back to the engine. Turn on the hose and watch your core cough up some horrible junk! Your all set now... Nick

I just purchased a 91 YJ with the same symptom. The gage shows that the engine is warming up but it does not blow any hot air. I topped off the rad and overflow and then took it for a little ride, still no hot air. Other posts mention disconnecting hoses and attaching a garden hose to wash out any blockage. Mike, you definitely seem to be the man in this forum. I am a newbie, but I can follow directions. I would like to try to flush out these hoses to see if they are blocked. Do you think you can provide me with some clear directions on this? It seems like a relatively simply procedure, I just don't want to disconnect the wrong hoses. Where exactly are these hoses located? Which end do I disconnect? Thanks, I have learned so much reading your posts for about a month. Thanks again - Mark

Mark, There was a post I read while researching the problem. It described feeling the hoses to determine if the core is blocked. If it is blocked, one will feel significantly hotter then the other. There were also many people that warned that if you use too high of a pressure, you will blow out the core.

Pick up a copy of a Chilton or Hayes manual. The graphic make it much easier to understand what is described in the forum.

CTM

I fixed the problem. It was actually a whole lot easier than I had imagined. I unhooked both heater hoses (from the engine end) and attached a garden hose (with an attachment), ran the water and repeated on the other hose. There really was not much to it. I was expecting huge globs of stuff to flow out, never really got any; I just waited until it looked like it was just clear water flowing through the hoses. Hooked everything back up and I had heat. Being a newbie, I was just hesitant but it was really extremely easy. Thank you everyone for your advice. This forum continues to teach me loads.