Debating between general and LT1 tech, but here it is.

My fans will not come on. I've checked both relays, continuity between PCM pin 10+11 on the red PCM connector and the fuse box, power and grounds everywhere, and I jumped two pins to bypass the relays and the fans came on. The coolant temp sensor on the water pump is working just fine, it's reading out on my scanmaster. Temp has reached 195 and stayed there for at least 5 minutes, the PCM is tuned to turn on the fans at 160. The only thing left is the PCM itself, can the PCM relays be replaced or do I need a new PCM? Am I missing anything? And thanks to Shoebox for his handy diagrams and wiring harness pics.

 

Do you have A/C? If so do they come on when turning A/C on? Might point to relay issues?

 

I have AC but the clutch is bad, turning it on will not attempt to turn on the fans. I've also checked relays and they're working fine.

 

Monitor your fan relay wires with a meter (looking for ground) while the temp reaches and goes beyond what you are programmed for. Not sure if your Scanmaster can tell you if the fans have been commanded on or not, but most other scanners will. If you see that the PCM has commanded the fans on and there is no ground being sent to the relays to operate them, then it would seem to be a PCM problem.

The other thing to verify is that the programming is actually what you think it is.

 

ScanMaster will not indicate fan status.

Just curious... why would you set the fans to come on at 160*F? If you are running a 160*F t'stat, the t'stat will not open fully until the coolant reaches about 180*F, you will have limited coolant flow, and your fans will be running all the time, when they really don't need to.

 

The fans apparently never stopped working. The car overheated a few days ago after I warmed it up and left work. Less than a mile from work the temp was approaching red line and I shut it down. Coolant was boiling from the reservoir so I let it cool down on the side of the road for 45 minutes or so, then I quickly drove it back to my mechanics hangar. I replaced the water pump and got a new stock 190 stat to fix the problem. After replacing everything, bleeding the system, and letting it get to operating temp I realized the fans didn't come on. I let it run for 10 minutes or so and the fans never came on and the temp reached 195 (scanmaster temp) for a while. At this point I thought the problem was never the pump/stat but the fans.

Today I drove it home to get it out of my mechanics hangar and lo and behold, the fans came on. My .bin file says the fans should come on at 190 (for some reason I thought it was 160) I have no idea why they didn't come on while the car was on jack stands, but there it is. I probably spent 4 or 5 hours troubleshooting a problem that didn't exist. Problem solved, and a giant facepalm for me.

 

Stock 'stat is 180. Did you mistakenly put a SBC one in?

 

Nope, it's the elongated looking mushroom one that the car is supposed to have. The parts store had it listed as 190 degrees

 

Stock is 180*F. I still have the one I took out of the car 14 years ago when I replaced it with the Hpertech 160*. It has "180" stamped on it.

Just to verify the appearance of the t'stat:

Courtesy of Shoebox

http://shbox.com/1/tstat.jpg

 

Yes, that's the one. I did the same thing, keeping my stock t-stat when I put the 160 in for a later reference.