Overheating at high speeds

cmbaker1 · 08-10-2008, 04:34 PM

I have a 98 TJ 4.0L that about a week ago started overheating while driving down the interstate. It will run fine for about 10 miles or so but then it will just start climbing very rapidly. When driving at lower speeds it actually runs a little cool. ( a little to the left of the 210 mark).I can drive all day in stop and go and never have a problem. I'm pretty sure the thermostat is good because i can watch the temperature drop in regular intervals. The system was flushed around 2 months ago but i just started having this problem last week. Any help would be greatly appreciated.

Red04X · 08-10-2008, 05:04 PM

Check [with engine off] if you can spin the fan by hand. If the fan clutch is locked up it won't allow as much air through at higher speeds. That's all I got.

XXRider · 08-10-2008, 05:11 PM

I doubt it is your fan as at highway speeds enough air should be moving throw the rad to keep it cool. I'd guess your rad or water pump.

Red04X · 08-10-2008, 05:22 PM

That's my point, at higher speeds the spinning fan will block the air from moving though.

bonza · 08-10-2008, 05:26 PM

Quote:

Originally Posted by XXRider

I doubt it is your fan as at highway speeds enough air should be moving throw the rad to keep it cool. I'd guess your rad or water pump.

I agree. radiator or water pump.

**Jerry Bransford** · 08-10-2008, 05:33 PM

If you've mixed the antifreeze with tap water for very long, the radiator could be clogging up with mineral deposits (mineral-free distilled water should always be used). You can usually see evidence of deposits by draining enough coolant out so with the radiator cap off, you can look down through the radiator opening with a flashlight to see if they're building up around the channels. If it is blocked with calcium deposits, the radiator has to be replaced. Radiators can normally have such deposits chemically and mechanically cleaned out and rebuilt by a radiator shop but the TJ's cannot. The TJ's radiator has a plastic top & bottom that is crimped to the aluminum core and once that seal is broken, it can't be made water tight again as a conventional all-metal radiator can.

Have you gone through any mud where the radiator might be partially packed with mud? If so, a coin-op car wash pressure washer can clean it out.

And if you're seeing any weepage from the water pump, that's a sure sign the water pump is failing. Good luck on this.

cmbaker1 · 08-10-2008, 11:10 PM

The fan seems to be working fine. If there was a clog in the radiator would i not also be overheating at low speeds. My guess is that it must be the water pump but I'm not sure because if the water pump was bad i would have more problems at low speeds but i run much better at those speeds.

97 SRH Jeep · 08-10-2008, 11:31 PM

shake your fan and feel if you can feel any free play in the shaft of the water pump. if so new water pump

happycamper · 08-11-2008, 12:08 AM

I have the same problem with mine, and Ive replaced my radiator, water pump, and thermostat , next will be the fan clutch

sheaster · 08-11-2008, 05:11 PM

I also seem to have the same symptoms. It's not the thermostat or motor cause I had to replace both of those

. Water pump seems to be working properly, but it may still be the culprit. So the consensus seems to be the radiator, water pump, or fan clutch with fan clutch leading the way.

**wushaw** · 08-11-2008, 05:38 PM

fan clutch

**Divinitous** · 08-11-2008, 06:25 PM

Quote:

Originally Posted by wushaw

fan clutch

@ highway speeds the fans clutch will just freespin. You'll notice this if you sit in the driveway and rev the engine. At a point you'll stop hearing the fan.\

Sounds like...

Clogged radiator
Water pump blades are worn

If you're going to replace the radiator make sure it's all metal and you might as well replace the hoses while you're at it.