My 2000 C5 is overheating, the fans do not turn on, I have changed the temp sensor and relays but fans still will not turn on. Fans will turn on if the relay is manually enguaged and cools down right away.
Any ideas on what may be the cause of the fans not working?

 

Here is a 98 cooling schematic. Check the basics (fuses and grounds) and report:



The fuses and relays on yours may be different numbers.

You can ground the PCM control inputs and that should turn on the fans

 

If you turn your AC On do the fans run??

 

8Vette7 (Chuck) is an expert in this area. Chuck, is it not also possible that if one motor is bad (open circuit) that it could also cause his problem?

 

Bill with ac on fans do not run.

 

Replaced all 3 relays and fuses are good. Fan on right side will only run on low for a few seconds then stops and wont come back on while car is running.

 

I checked all the items you reccomened and i also replaced the t-stat and coolant. i do not know if maybe the conector was not on properly i did make sure both fan conectors were on good and after replaceing t-stat i let car run until it reached 225 and fan did kick on and also turned on ac at differant temps and fans did kick on. So don't really know what was going on but will drive car and see how it does, will undate with any new info.
I sure do appricate the help, Bill is a great help also. Thanks Again Guys!!!!!

 

Sounds like the fans are working as designed now. Under what conditions did you feel the car was "overheating"? What temp did it get to? What was the ambient temp? Do you have any modifications to the engine that would produce more HP? Did you change radiator fluid and "burp the system"?

I've been watching my temps closely, my car has been modified with twin turbos and tend to overheat if I run it in high rpm mode like at the motocross track. I have an oversize dewitt radiator and will be adding an electric water pump and an upgraded fan set. I also run a SacCity coolit V3R.

On normal day to day driving if I don't get into it the car will run between 196 to 201. If it is warmer than 70 and I spool up the turbos the temp will rise to 205 to 210 then fall back once I'm off the gas. On the highway at 80 mph and 2000 rpm the car runs between 198 and 200 depending on temps. As you read more on this subject you will find that these cars are designed to run hotter than what we have been use to from earlier model cars.

One more thing. If you have not done so clearn out your radiator with a pressure washer. Then install a wire mesh screen under the front dam. The design of the air intake is like that of a quality vacuum cleaner (insert brand name here) it will pick up every piece of paper and plastic bag it rolls over. I was amazed when I went to install my screen I found a styrofoam cup and the front page of the news paper. Guess the guy I was following was having his morning breakfast.

Good luck