Hi, this is my first post. I have 1995 Yukon4x4 5.7liter gas I purchased 5 years ago. I have put 15k on it since I purchased it. It has been a great running truck. The temp gauge has always read around 180 give or take a 2 or three degrees under all conditions. I do not loose any coolant and the truck seems to run great other than the overheating issue. The coolant appeared clean and theres no sign of rust anywhere in the system.
Last fall while driving on the beach in sand it began to run a little warmer than norm(195 or so). I didnt pay it much attention. During the winter all seemed fine. When spring came, I noticed it was running 200 or so. Being proactive and knowing I pull a camper (3600lb), I put a water pump on. It didnt make any difference. I put a radiator on it and it made no changed at all.
Went to the beach in early may (no camper). While driving in the sand the temp woud climb to 220 sometimes 230. It usually would take less than 5 minutes to get that warm. I also believe if I had continued to drive the tempeture would have continued to climb. I would stop or get out of the sand before it got any hotter and it would slowly return to 205 or so.. On the way home from the beach it ran 205 to 210 it was also a hot day on the trip home.
After getting home I put a thermostat 195 Failsafe on and it made no changed at all. I removed the transmission line from the radiator and ran an extra trans cooler as a test to see if the trans fluid could be getting hot. That made no changed at all. I purchased a sunpro temp gauge and installed it and it read the same temp as the factory gauge. I had the catalytic converter check to see if it was clogging and it came up as good as new. I put a new 15lb stant radiator cap. I burped the system several times. Iput in new hoses.and belt. I let the thermo cycle with the cap off and never seen any bubbles and to see if it appears to be flowing good and it appears to flow fine. The fan clutch was checked by me and the mechanics. When cold it will turn only as far as you turn it with your hand. It sounds like a jet under the hood for the frist minute or two after starting calms down and when it begins to run hot it is the same jet sound.
Being frustrated I took it to a local shop I trust and they keep it fir a week and couldnt pin it on any paticular thing. They said it could be the heads leaking(no water in the oil or oil in the water}.I ask would that fix it and they said it MIGHT fix it. I got the truck back and decided to take it to a radiator shop who has been in business since I was a kid (i am 44yrs old). They cannot find the problem. They did a compression test on the heads and said they are fine. They took the radiator apart to ensure something wasnt clogging it up and it was fine.
Some other symptoms: While driving if I give it wide open throttle it will rise 10 degrees or so and then fall back to 205 or so within a minute or two. The normal temp seems to change with the tempeture outside. in otherwords. 80 degrees outside 200 to 205. 70 degrees outside 190 to 195 and so on. Any time under a load it begins to climb to 230 or more. I did let it get to 250 once.
I am at complete loss. I have done so many things to it I may have forgot to list them all. Although I am not a mechanic, I have done nearly all my maintainance on all my autos since I got my first car. I dont know what else to do. I dont know what else to check. Posting on a few forums is my last attempt. Any input or thought will be greatly appreciated.
Thanks Monroe

 

what are you using to measure the temp? If it's the guage on the dash have you considered the guage and sensor are both 15 years old?

I have something similar where my temp guage would jump around on my '95 tahoe.

since it was 14 yrs old at the time. I just didn't care any more... (sold it for a 09 tahoe)

But I would check the temp sensor... that seems the most likely to go.

I had a similar problem w/my one jet ski... kept stalling on a 'full' tank. the tank was never full. the gas guage was / is busted.

 

I have put a sunpro gauge on it and it reads the same as the factory.
Thanks Monroe

 

what would happen if you just took the thermostat out? (for testing)

 

The radiator shop took the 195 tstat out and replaced it with a 180. I got it back this morning and it did run roughly 10 to 15 degrees cooler under a normal load. Which is almost normal. I did a test i ran the truck about a 1/4 of a mile similateing what the sand at the beach is like by using the brake pedal. trust me I didnt get crazy with it or anything. I actually think I took it easier thn the beach would be on it. Within that 1/4 mile rinning in second gear and the rpms at 2100 running roughly 20mph it got to 220 degrees. I believe if I had continued it would have continued to climb. I am considering taking the thermo out completely to see what would happen. My next day off work will be wednesday. I appreciate any ideas to get me ready for that day.
Thanks Monroe

 

Normal operating temp for all vehicles is 210-220. Some cars do not turn the electric fan on until 227

 

fan clutch?

 

Waterpump?

 

A lot of other people on this and other boards seem to think it is the fan clutch. that is one thing I plan to replace.
I understand 200 to 210 could be normal for some vehicles. I could agree with that except for the prior 3 years or more it never under any conditions move over 185 to 190. Now it stays at 200 and will go to 250 or more when under any load at all.
Thanks Monroe

 

With my aunt's '99 Suburban with a 350 it overheated on them in similar ways that you listed. It ended up being the intake gasket was bad and would leak coolant inside the motor and mix with the oil. I would check your oil to make sure there isn't any antifreeze in the oil. I'm not sure because if you've done all of this already you might have checked the oil several times but after we replaced the intake gasket it's fixed and runs at normal temps now.