Another overheating coolant system post

I recently bought a '98 XJ with the 4.0 six. The coolant was really dirty when I got it so I did a system flush, replaced the original upper and lower hoses, heater hoses, thermostat and gasket, and radiator cap (16lb Stant). Within 200 miles of doing that I'm having intermittent overheating problems. There were no overheating problems before I swapped out the grungy antifreeze.

It seems to come up to operating temp just fine and will hold at about 210 for quite a while. But when I take it out on the highway and run it for 10 minutes or so the temp will suddenly spike up into the red. It'll sometimes hold there for 30 seconds or so then come back down fairly fast. Other times it'll go up into the red and stay up there till I stop and let it cool back down.

Running the heater full blast doesn't make any difference on whether the temp changes. Running the A/C doesn't either. It's not just a temp sensor because it is getting hot enough to blow coolant up into the overflow bottle, and it's boiling hot.

Anyone got any speculation as to what the problem may be? :banghead:

Thanks in advance!

I had a '93 that was having scale build up inside the radiator. The scale eventually broke off and partially plugged up the radiator. Maybe when you flushed it out you knocked something off and have a partially plugged radiator.

This can be checked by a pressure check by a local radiator shop.

StraightToPlaid said:

I had a '93 that was having scale build up inside the radiator. The scale eventually broke off and partially plugged up the radiator. Maybe when you flushed it out you knocked something off and have a partially plugged radiator.

This can be checked by a pressure check by a local radiator shop.

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Yeah, I wondered about that too.... or sludge.

So far there's no water in my oil, and it never misses like it's getting fluid in a cylinder. That makes me feel a *LITTLE* better.

Thanks :wave1:

With the poor condition of the coolant before I would suspect quite a bit of rust in the system. That said, and the fact that you're overheating at highway speeds does indicate a limited coolant flow. However, instead of suspecting bits of crap plugging things up, I would think that the vanes of your water pump are quite corroded if not eaten away altogether (so it's not working to push the coolant) or just the general condition of the radiator is FUBAR. It could be loose crap though and one way to find that out is to get ahold of a IR gun and look for cool spots on the radiator.

When you did the flush did you flush out the heater core separately? If the coolant was as bad as you say it's likely the heater core is also plugged up.

I would check to be sure you are in fact full of coolant. The quick up and down temp spikes makes me think it might not be full.

98stocker said:

I would check to be sure you are in fact full of coolant. The quick up and down temp spikes makes me think it might not be full.

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Yep, it's full.

Another thing I forgot to mention is... it never runs bad, loses power, or starts missing when it's overheating. There's no white smoke out the tailpipe or anything like that.

I'm going to dig into it today and figure this out.

:thumbup:

yeah there must be a clot somewhere - what kind of shape is the radiator in? something came loose and i bet is lodged somewhere....

oh and check out the tstat - it might have gotten stuck

aparke4 said:

yeah there must be a clot somewhere - what kind of shape is the radiator in? something came loose and i bet is lodged somewhere....

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The radiator is original so I'm betting that's where the problem is. I may just opt for a new one from radiatorbarn.com... might as well swap out the water pump while it's apart. It's only money right?

UPDATE: Fixed!

The radiator was full of crap. Some sludge, some pieces of... stuff. When we did the flush it dislodged a lot of stuff. The radiator also had a bend in it from a deer/jeep accident a while back, long before I got it. Not really sure if this contributed to the problem, but I'm sure it didn't help.

New radiator and a new fan clutch and this thing is running steadily cool.

Lesson learned: When you're flushing the cooling system out don't just flush it a little and assume you're good. Take your time and really flush it good. I'm not sure this would have saved me, but it may have.

Thanks for the input! Over and out. atriot:

cool man glad it got fixed