88 Suburban over heating stumps all

I have a 88 Chevy Suburban 4wd 350 v8 that has stumped two garages as to why it continues to overheat and boil. The temperature flutuates from normal ( under 210) to well over 260 (way past the red), my first reaction was that it was just the gauge, but the vehicle does over heat and has blown the radiator and boils and bubbles. I have had the vehicle in the shop three or four times in order to find the problem. I have had the radiator replaced, upper and lower hoses, thermostat (three times, each mechanic tries that first), have a new heater core, and the water pump is new. The engine has been pressure tested multiple times, the head gasket has been checked and yet it still overheats. Here is an example of what it will do: When starting the engine, it will heat up normaly, but it will quickly all of a sudden heat up and the gauge will go right into the red. The needle will stay in the red for a period of time and then rapidly drop down to normal operting temperature...a few miles down the road the guage will once again rise and either stay in the red or go past and start to boil, and then drop again. It does this consistantly either going to the red or going past. My only solution is to pull over for about three or four minutes and then start the engine again. Once the engine is started (gauge still indicating running hot), I gas it a bit and it will once again drop down. This seems to happen no matter what type of driving I am doing, highway or city, towing or not. This has stumped many...I would appreciate any help I may get, thank you in advance.

Presto31

try a new clutch fan, i now it sounds stupid, but that is what my overheat problem was.

Yes I would look at the fan also. Has there been a other motor work done to it in the last year??? Like freeze plugs ?? Was the rad cap pressuse tested to 16 psi and does it hold pressure. I hope you dont have pure antifreeze in it . Is it mixed with water??
Are you sure the water pump is working? Or the block is filled with gunk and causing a coolant flow problem

I have the same exact problem right nowin my 89 Suburban/350TBI/700R4/4x4. It f***ing sucks! I have no idea what to do. Have you found any sort of solution? I don't know much about trucks I guess but dosen't the fan just keep airflow over the rad when sitting still with the engine running? Wouldn't there be enoug airflow when we drive at 40, 50, 60mph+? Please help because I am overflowing enough coolant to kill a whole neighborhood of dogs.

I also say look at the clutch on the fan and if you replace it go with the super duty clutch. I had the same problem on my 92 and it was the clutch and it sounds like everything else is new. The only other possibility would be a clog in the engine, But I doubt it.

I would have to agree. I had the same problems and sure enough the clutch on the fan was bad. Stumped me for a few too. Then I realized when reveving the motor the fan did not pick up speed very fast. It sounded like new again when I replaced. Could hear that famaliar whine that I didn't realize I wasn't hearing any more.

Jcasey22 There may not be enough air flow while moving at any speed. The Clutch on the fan is to help fuel economy (like there is much on these beast) as the air rushing through the radiator helps make the fan spin easier.

When its overheating go to the rad (with the engine off) and feel all over it and see if there are any hot and or cold spots. If there are cold spots the rad has a clog in it

As Fireplug said, There may be a clog in the radiator, What you can do is check the radiator with a pyrometer, There are some you just point at different parts of the radiator and record the temperature differences, There should not be too much of a variation on a good flowing radiator, But if it's clogged you'll have a "cold" spot.

I'm just wondering if the Water Pump is rotating in the correct direction. Didn't the cooling system pump reverse direction when they went to serpentine belts?? Check flow direction for the pump.

Larry

I dont know if a late model reverse flow pump was used or even if it fits but you might want to see if you have the right pump. Was it overheating before water pump was put in.

transmission oil how is it. if its low you will overheat the motor. I know it sound strange but it happens.

I had similar problems and replacing the radiator cap fixed it.

replace clutch fan with regular. if that doesn't wprk remove thermostat.

Has a leak down test been performed? From your description of the problem, it sounds like a head gasket leak or even a cracked head/block.

//2000CAYukon

with the rad. cap off look to see if you're getting flow if you are it's prob. the clutch fan if not the water pump maybe

replace clutch fan with regular. if that doesn't wprk remove thermostat.
Try to do what 84fiero123 suggested, or try this, take of the thermostat and try to drive it and see if doesnt overheats, if it does check the water flow

did u change anything on the front of ur truck valences grills brush guard any thing if the air flow is changed it will over heat

Hey, put a supercool radiator in there. they make them for the diesel suburbans, it will fit, guaranteed not too overheat then

Once a thermostat has gotten hot, it's bad. A wax pellet inside the thermostat expands and opens the thermostat. When it gets overly hot, the wax leaks out and the thermostat will not be able to open as far as it should. What caused the initial overheating in the first place could have been a bad fan clutch or a clogged radiator. I'm not sure how the garages could have checked the head gasket but it sounds good..... Radiators over five years old don't cool as well. Make sure the fan shroud is still in place.

This post has been around awhile but I just came across it, so in the intrest of helping anybody with a similar problem in the future:

I there is a pocket of air trapped in the cooling system it will cause violent temperature fluctuations. The temp can rise to extreme heights only to magically come crashing back down to below normal temps, only to repeat the cycle. ususally in cold weather it's more pronounced, in warmer weather less so.

I had this very same problem and suffered with it for years. Only after working on later model vehicles that have air bleeds in the systems did I finally realize what was going on. If any part of the cooling system is higher than the pressure cap, it will cause air to be trap. This can be as simple as a radiator hose, whose curve is above said radiator cap! As was the case with my car!!! This is also why a pressure test doesn't reveal this problem. All that it took to correct the problem was to push the radiator hose down below the level of the pressure cap and vent it. This in effect purged the offending air and returned steady temps for me to enjoy! To permanently correct this, turn the radiator hose, or get the correct one, or find the cause of air to ge trapped in the system.

Hope this helps. :)

IF all the parts have been repalced as you say and they are correct. THen I would look at the radiator fan clutch. THose metal radiator fans seldom wear out...but the fan clutchs do wear out over time and miles. I too wonder if it has the correct water pump? If the head casket is ok and no-one suspect a cracked head or cracked block. One assumes the thermostat is installed correctly? How many miles on truck? So it passes the pressure check with no problems? IF my truck I would be tempted to replace the waterpump myself to make sure its the right one. Trucks with the serpatine belt (large single fan belt that drives all the accessories) take a different water pump than those with the old style mult-belt setup. I beleive that year model truck was one of the first with the serpatine belt system? Car repair shops should know this.

DO a simeple check yourself..... Engine cold, open radiaotr cap and check fluid level, make sure full or and inch or two full from radiator top. Start engine and leave radiator cap off. Monitor guage and coolant flow throug radiator....when truck reaches operating temp you should see the coolant flow increase when the thermostat opens (verifies the thermosat operation) and also water pump operation.... you should be able to feel air being pulled across the radiator fan. Take a look at the radiator fan to make sure its moving properly and you don't notice it "wobbling" around.

When truck is hot and you driven it...do you ever hear the fan clutch engage? you 'll notice this by the large increase in fan noise when you start from a dead stop or at slight increases in rpm at lower speeds. At higher speeds and higher rpm level its a little harder to determine when the fan clutch engages. YOu ususally feel a little power drop in the engine too, when the fan clutch engages.