First off, I drive a '99 cherokee with the 4.0. I just replaced the thermostat because it was sticking. No problem there, works fine. But now my heater wont get hot. Its way to damn cold to be driving around without a heater this time of year so I need to fix it asap. I took the day off work so I need to do it today.
I checked the water hoses from the pump to the heater area. The pump is puting out water just fine but it seems to be that it is getting blocked off somwhere at the heater. I think it might be the heater thermostat but I really dont know. Hopefully someone here can help.
If there is water coming out of the heater core supply hose going into the heater core (when running=water pump working) and the engine is at it's correct operating temp, it sounds like the core is blocked by some crud.
Disconnect the hoses (carefully or you can break the core and cause much more pain!!) from the core and using a garden hose try to flush water each direction into the core. Eventually you should get it to start flowing and a bunch of garbage should come out. Keep flushing until you get good flow in both directions, reconnect hoses and top off coolant as necessary. This is what I have always done and unless the core is so full of concrete crud, it works most every time. You might want to consider flushing the engine as well or it can plug itself up again...
An air bubble in the system from the thermostat replacement would be my guess as the source of the problem. Check the radiator and see if the fluid is at the correct level. Leave the radiator cap off, turn the heat on, and start the engine. Keeping yourself and your clothing away from any moving engine parts, squeeze the upper radiator hose a few times every 30 seconds until the thermostat opens. Have some coolant on hand in case the coolant level drops. You will know when the thermostat opens, a small amount of coolant will surge up and overflow. When this happens, simply grab the radiator cap and install it.
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Did you make sure the tiny hole in the thermostat is up to enable air to evacuate?
Check the heater hoses, both must be hot to the touch.
If not, see ^ Was the heater warm before you changed the thermostat? If not change the water pump too.
Flush the heater as mentioned earlier and you should be good. Its a common problem.
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Originally Posted by speedbucket
perfect depends on how far away you are when you look at it:D
Originally Posted by Millermagic
It's a 4.0 ... as long as there's something in the crank case that isn't coolant I'm sure it will still run forever.
it has always ran a tick over 200 and still does. I did some more tinkering and got the heater cleaned out but now I think the radiator is clogged. Im gonna take it to the shop tommorow and have them flush the radiator and motor and see if my problems stop. Its pretty nasty for sure.