Way to hot 95 Suburban!

I would verify water temp and oil pressure with mechanical guages, to see what the actual temp is and *IF* the oil pressure is going up and down. Is the fan running (if electric) and then have the radiator removed and checked for flow. Post back results.

No

You could check pressure with a manual gage but this is not your problem

Cooling a engine is not rocket science. First I do not see a new thermostat on list as they can fail and cause heating issues. Second, normal flushing system does not remove deposits that can build up around radiator core tubes and block flow. It takes a acid flush or a trip to radiator shop to clear that. (A radiaotr shop could flow test it and that would show if it is plugged internally) Next make sure external core stack is not plugged up with dirt and bugs. Another classic problem is that the clutch fan goes out of calibration. As long as the bearings in them stay good and fluid does not leak out, they never wear out but the Bimetal coil on them can age and as it does it raises the engagement tempature of the fan. Many simply replace fan clutch but it is easy to reclaibrate tham as I have been doing it for years. You will find info about how to do this in link below.

TheSnoMan.com

I will go get a new thermostat tonight. I am assuming (you know what that means) that I need to get a 200 deg thermostat. As for the radiator, the exterior of the radiator is free from bugs, dirt , etc. Being twelve years old, it might be better to replace the radiator?. There are two fans, one is smallish and located on the front of the radiator, the second one is the main and was running when i looked at it earlier.....

Test it on the stove by putting it into boiling water. Make sure it opens all the way. It would be helpful to have a thermometer to check on when it opens. I *always* test the thermostat this way, whether I'm reinstalling the old one or a brand new one.

With everything shut off put a light behind the radiator and see if you can see it through the radiator in a number of locations. Worse case scenario, ask the wife for a hand held mirror.

Sounds like he has a 454 (aux cooling fan). If thermostat does not fix it (and it should be a 190 not 200) it is either a plugged core internally or a clutch fan out of calibration. (take note of how hot engine gets before clutch fan gets really agressive) If you replace radiator, get the thickest one you can find to replace it.

----------------- TheSnoMan.com

I replaced the thermostat with a new one. At high idle it stayed at

190-200 degrees. I ran the truck at high idle for approx ten minutes. The temp did not change until I took it off high idle and it went back to low idle. The the temp moved up to 210 again. I can see light through the radiator so either it is internally clogged or the fan clutch is bad. From what you guys are saying and with the temp dependent on how fast the fan is turning, it seems like the probable culprit is the fam clutch. I did not realize that the fan was variable, I thought that it was either on or off.

Still not sure what you concluded....if it is an electric fan(s) do a check on when the fan(s) come on in relationship to the engine temperature. There is a sensor that measures the water temp and turns the fan(s) on. Mechanical fans (driven by the belt) have the fan clutch. Any checking on the oil pressure. It is normal to have 30 psi or so at idle and a higher reading at higher rpm.

The fan is driven by the serpentine belt. Tomorrow, I will check the fan clutch to see if it is working properly or not. I do not have a mechanical gauge to check the oil pressure with, I will have to get one from one of my buddies.

Clutch fan are indeed varible in operation. The bi metal coil controls a valve that let fluid into clutch area and centrifical force sends it back to resevoir. The clutch fully engaged when it lets fluid in faster than it can be pumped out. Also at a idle most clutch fans do not always move enough air to keep things cool at times especailly in hot weather. I have a 200 K3500 that seem to be the exception to this rule though as it has a 10 bladed clutch fan and it keeps its cool no matter what you seem to do with it. The clutch is also aggressivly calibrated because you can hear it engaging from time to time on a hot day even at speed. Temp never hits even 210 on it.

----------------- TheSnoMan.com

With the mechanical gauge you will eliminate a possible electrical problem with the gauge itself or its sender. Good luck!

Ok gents, I THINK that the problem has been fixed. I still have not checked the actual oil pressure with a mechanical gauge but I think that the problem was with the fan clutch. I went ahead and bought a new clutch and installed it. Now when I go up a hill or sit still for too long, I can actually hear the fan get aggressive. I am going to go for a drive in the hills to see if I can get the temp to go up. Just driving around the block (4 mile round trip), the temp would not go above 190.

Cool Beans!

It kinda sounded like a clutch fan problem and as I said the bimetal coils on them do age and raise engagement temps and can cause problems just like this.

----------------- TheSnoMan.com

The problem has been SOLVED. I drove my truck to the dam today towing my boat, uphill, downhill, steep, and very curvy. The temp never got above 190. Thanks for all of your advice and help gents. I never would have guessed that the fan would have that much effect.