1998 Chevy Z71 Overheating Help!!

Collapsing hoses..

Make sure the clutch fan is working properly, as they do go bad. If it is okay, you may have a plugged radiator core but my nickle is on the clutch fan.

Two good clues have already been posted.

If the fan clutch is the issue, it should only overheat in slow traffic or when idling. At highway speeds, you get enough cooling, usually, even if you had no fan at all.

Sometimes the exterior fins of the radiator will get blocked with grass clippings, leaves, paper, 'love bugs' or other detritus. This can occur between the air conditioner condensor and the radiator sometimes so you have to look carefully.

Some engines are really bad about holding an air bubble when you think you have them full of coolant. You have to be careful you get this bubble out.

An internally blocked radiator or a bad radiator cap can also be issues.

Last, if you have eliminated everything else, you have to consider an internal engine problem. If you have a cracked head or block, or blown headgasket, hot exhaust gases can enter the coolant and heat you up fast. You don't always see oil in the water, or coolant in the oil when this happens.

Some GM engines have some well documented 'weaknesses'. Which engine do you have?

I wish I knew how and where to do an FAQ on this subject, since there has been a lot of conversation this year about overheating.

At highway speeds mine runs very hot, always has. I agree with you. What might be my problem?

I really appriciate the feedback and so fast. Here we go I checked the clutch fan it is working properly... the hoses dont seem to be collapsing but in this instance i think it would be safe to go ahead and replace them. I was really thinking it could be something blocking internally in the radiator so I am going to flush it really well and see if that fixes the problem. Also just to throw this out it is not getting hot just idleing it when you go and drive it it fluxuates up and down it will be really hot and then drop 60-80 degrees and then continue to go back up again. Again thanks for all the help

By collapsing hoses I meant internally. They separate inside and block the flow....

How did you determine that it was working properly? Does it engaged going down the road when engine get hot? It should as it just does not work at a idle and low speeds. Lots of times they get weak and do not cool properly. Also you cannot relie on ram air to keep it cool all the time. My 2000 K3500 never gets hot no matter what I do but it has a 10 bladed HD clutch fan and a 4 core radiator and I can here the fan coming in and out on hot days towing on highway keep temp under 200. It will be

6 this winter and it has not hit 210 yet. Proper clutch fan operation it VERY important for proper cooling becuae ram air will not cut it a lot of the time on a hot day with A/C on

.... not getting hot just idling when you drive it it fluctuates up and down it will be really hot then drop 60-80 degrees then go up again. __________________________________________________

This can be caused by a failing thermostat.

Rodan.

Well, he said he replaced the thermostat, but he could have gotten a bad one off the shelf, I guess.

I am wondering now if he is really overheating, or whether the gauges are falsely indicating a fluctuating overheat. That would be important to be sure of.

If he took off the lower radiator hose, and flushed the radiator with a garden hose, he might be able to estimate if water is passing through the core readily. If not, take that puppy out and head to the radiator shop.

Assuming the radiator is okay, then we are beginning to move uncomfortably close to an internal engine problem.

Er, Snowman, the viscoelastic fan clutch works at optimum when at idle. It slips at high speeds because the engine doesnt need the coupling as much.

When the surrounding air temperature increases, the thermal element allows a more direct coupling of the oil filled clutch and lets it regulate temperature a little better.

You can give a simple test to a viscoelastic clutch. With the engine off, just try to spin the fan. If it moves, but you feel the drag, then the clutch is most likely okay. If you feel no drag at all, it is probably bad. If it is totally locked, that isnt good.

By the way, snoman... that is a nice site. Did you set it up yourself, or did you have a computer consultant do it? What kind of software is needed?

You are looking in the wrong places. Replace the clutch fan and I will bet your troubles will go away. Your simptoms match a bad clutch fan almost perfectly. Or you can keep spinning your wheels. Many years ago I had a plow truck start to overheat badly one winter. Turned out to be a bad clutch fan too though my first choice then was thermostat.

Did it myself. Contact me through my site if you want more info on it.

Its easy enough to check the fan clutch.

Not always, if you cannot hear it running with a vengence when engine gets to 210 or so even while going down the road, it is bad. The one on my plow truck "looked" okay but it was not. A good HD unit can hold to

3000RPM or more when needed to cool the engine.

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are

Well, he needs to check it certainly. If it is overheating at highway speeds, I sincerely doubt it is the fan clutch BUT I have been wrong before.

I do not as I have seen it. Todays trucks have smaller grill opening and are tighter packed under hoods to and on a hot day on hiway with A/C and some drafting behind cars or truck or going with the wind it can else happen when clutch fan fails.

Please let us know what you find.