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running hot help please!

2K views 14 replies 10 participants last post by  Themhylands 
#1 ·
Ok so I have a 94 yj with a 2.5L. I started having issues with it running hot and acti8ng like it was the thermostat by all of a sudden dropping from 250 to 190 with in a second. So I changed the thermostat and problem persist. I have since changed the water pump, temperature sending unit, temp gauge and 3 thermostats and still the problem persists. I really do not know what else to do because as long as the thermostat is not in it then it will not run hot but as soon as I put a thermostat in it it will run hot. Anyone ever seen this issue or know what it could possibly be? In my mind if it is the head/ head gasket then it would run hot even with out the thermostat which leaves with a bad radiator but even in that case it would run hot with out the thermostat as well right?
 
#2 ·
If the radiator has never been replaced replace it, its old and its clogged it has no choice its 20 years old and its clogged. If the fan clutch has never been replaced replace it its bad. They last no more than ten years and from what I can tell at the five year mark your on borrowed time. Its a part that needs to be replaced with time. When you remove the t stat you have a wide open hole and increase water flow. That will just trick you like it did me. You also need a good fan shcroud, fan blade, full of coolant and a turning water pump. After running a garage for three years I have found that most engines fail because of running hot. Dont chance it its no worth loosing your engine. Advance auto will loan you a cooling system pressure tester so you can check the head gasket for leakage. Read up on how to test it. Let us know what you find.
 
#3 ·
It could be a bad fan clutch, or a plugged up radiator. I would check the fan clutch and forward and reverse flush the cooling system before tossing more parts at it. Odds are at that age both could be bad but you might get lucky with reverse flushing the cooling system and checking the fan clutch.

i have a vehicle older than that with the original fan clutch, heater core, water pump, and radiator. The vehicle has been very well maintained and I'm the original owner. I could also be lucky as well.
 
#5 ·
Well... I hate to jump in with all these "experts".... but I would AT LEAST test the thermostat I have, before going ANY further.

Also, none of these people have mentioned "burping" your system to ensure no air pockets.

Also, feel BOTH of your hoses coming out of heater core.... if you have good flow, one will be NOTICEABLY warmer than the other. Same goes for the LARGE hoses going from engine to radiator. Good advice on checking lower "suction" hose to see if collapsing (it CAN happen if spring is removed or shifts).
 
#7 ·
I have a similar problem. The hose from the engine to the radiator gets hot and the lower hose has the spring and appears in working order. I have flushed the system and replaced the thermostat. The temp gauge never gets above 170 but the check engine light comes on after a short drive. This is a 94 2.5 manual.
Thanks
 
#8 ·
BURP the system. You change the water pump. You need to let it run for like 15-30 minutes with the radiator CAP OFF. Wait for it to get to 190 or so and let it get all the air bubbles out like 15 min after 190. Then turn off, put CAP back on and test drive again. I had same EXACT problem after I replaced my water pump.
 
#10 ·
I was getting code 17. I replaced the tstat and it kept doing it. I flushed the coolant and it still went off. I am about to replace the water pump and sensor. The dash showed 185-195 but the light kept coming on. Top radiator hose was on fire and the lower was cool. 4th and 5th gear would go out and I could only drive around 30 mph to get home.
 
#14 ·
Are you seeing coolant flow in the radiator neck once the thermostat opens? Have you verified the thermostat is opening, and is fully open at 195ish, using a pot of water on the stove and a thermometer? Is the thermostat installed the correct way?
 
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