2001 Jeep Cherokee Overheating

DOCJAY78

MEMBER
2001 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
9,770 MILES

2 weeks ago I bought a 2001 Jeep Grand Cherokee with the 4.0l engine and 4WD. I drove it about 150-200 miles and then noticed it overheating down the highway, I was a couple miles from my house so backed off and went home nice and slow and it cooled down some, it got up to about 250 and then backed down to 240 til I got home. I let it cool down, topped it off with water and then let it idle in the driveway. It climbed again. I drove it around a little and it seemed to stabilize around 245 while driving, drove it about 15-20 miles. It was bubbling back into the reservoir. I did some research and found some stuff about the fan relay switch and fan relay. I checked that out and found the relay had been changed and noticed the fan kicked on at around 200. I assumed it wasnt that. I changed the thermostat, changed the hoses, flushed the system and put a safety radiator cap on it. It was fine while idling, so I decided to take it for a test drive. Within a mile it shot up to 245 so I turned it around and took it home. As I was pulling in the driveway, the temp went to 250 and then I heard a pop and the radiator blew a seam right below the upper cooling hose. I changed out the radiator, real carefully, and then refilled the system and it idles around 210, and I changed the radiator cap to a regular one, but took it for a ride and it rose in temp again. Around 245. Now not sure what to do, is it the water pump? Its not leaking and it isnt making a lot of noise. The truck isnt putting out a lot of smoke, no water in the oil, isnt losing coolant, no wierd smells inside the cab or in the tailpipe, and is idling smooth and runs smooth when it runs. I thought about getting a pressure test at a garage, but it overheats before I can get it to the nearest one. Any advice?

8 Replies

CARADIODOC

MECHANIC
33,741 POSTS

First thought was rotted / crumbling cooling fins on the radiator, but since you already replaced it, feel the radiator and heater hoses when it overheats. They should be too hot to hold onto for very long, but not hot enough to burn you. Also notice how hot the air is that's blowing out of the heater. If the temperature gauge reads hot, the heater air is cool, and the radiator hoses are cool, suspect a plugged heater core, a loose water pump impeller, or a leaking head gasket.

Some cooling systems require hot coolant to flow through the heater core to reach the thermostat. A way around this is to use a thermostat with a bleed hole in it or to drill a 1/16" hole in it. That will get the hot coolant to flow over to the thermostat. Sometimes you can remove just the upper hose from the thermostat housing, then reach in to prop it open as a test.

Broken water pump impellers are common on Volkswagens, not on Jeeps. You would see no flow through the radiator and the hoses and heater will be cool if the impeller is loose.

A leaking head gasket will introduce air into the cooling system. Thermostats do not respond to hot air. They must be hit with hot liquid. Your mechanic will use a special tool to check for a head gasket leak. Air is drawn through a glass tube with two chambers of dark blue liquid. If combustion gases are present, the liquid will turn bright yellow.

Caradiodoc

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Wednesday, March 10th, 2010 AT 5:09 PM

DOCJAY78

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The air coming from the heater is cold. The upper radiator hose is hot. I would like to get the gasket tested, but it is about 5 miles away and the jeep overheats after a mile or so. Should I swap out the water pump next? Any other signs for a bad gasket?

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Wednesday, March 10th, 2010 AT 5:41 PM

CARADIODOC

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If you start out with a cold engine, it can not overheat in one mile. I've nursed cars home already wth popped hoses by letting them cool for just 15 minutes, then driving about three miles at highway speed and coasting another mile with the engine off. If there's bubbling in the overflow reservoir in less than four to five miles, that would suggest a leaking head gasket. Proof would be a lack of steam with the bubbling. Also, the coolant in the reservoir will be cold.

When the radiator hose is hot, feel the heater hoses. If they are hot too, suspect a separate problem with the temperature door in the heater box. If the hoses are cool, remove both of them from the engine and try to run water through them from a garden hose.

Was your replacement radiator new? If it was used, look for deteriorated cooling fins.

Caradiodoc

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Wednesday, March 10th, 2010 AT 6:14 PM

DOCJAY78

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4 POSTS

Ok thanks. The radiator was brand new. I have not noticed any bubbling in the reservoir since I changed the radiator cap and the hoses and the radiator. But everytime I did drive it, I had let is idle for a while first. Ill try to get it up to the shop tomorrow for a pressure test before I do anything more. What about the water pump though, if the pressure test comes back negative, should I change out the water pump? Or is it a heater core problem more than a water pump? And if it is a leaky gasket, shoudl I get it fixed and replaced or use one of thos compounds sold at parts stores to fix leaky gaskets? Thanks for the help.

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Wednesday, March 10th, 2010 AT 6:23 PM

CARADIODOC

MECHANIC
33,741 POSTS

Let me clarify my previous reply. It's not a pressure test. I call it a "sniffer" test. The radiator cap is removed, enough coolant is removed to prevent any from entering the tester, then the tester is held over the radiator spout and air is drawn through the glass cylinder with a squeeze bulb. If the liquid turns bright yellow, combustion gases are getting into the coolant. If the test liquid becomes contaminated with coolant, it will not change color.

To prove the test liquid is working, it will change color by drawing air from the tail pipe or even by breathing into it. Drawing clean fresh air through it will return it to dark blue.

The heater core is a fairly common problem on a lot of different vehicles. Water pumps don't cause much trouble so save that for last. Run the garden hose through the heater core first as that doesn't require replacement gaskets or other parts.

By the way, as long as I'm thinking of it, look for something really stupid that can be done on engines with serpentine belts. Be sure the water pump is turning in the proper direction. In some applications, the belt can be misrouted to cause the coolant to be pumped backwards. Thermostat won't ever open then. There should be a belt routing diagram somewhere under the hood.

Caradiodoc