Is the aux fan supposed to run with the engine off?

Mine doesn't, but will kick on as soon as I turn the key when the engine is hot. If it is supposed to stay on, then I need to check the thermo switches.

Also, does the A/C switch for the aux fan sense the pressure of the system or the heat generated by the A/C system?

The engine is now getting warmer than it should on a 10 mile highway run (200F). I'm thinking the T-stat might be hanging up, so I've ordered a 75 C t-stat from FastLane. I knew I shoulda done the T-stat when I was in there!!!

The aux fan ought to only kick in if your key is switched on in the ignition. If the engine is off, it ought to be too.

Get the Tstat sorted and hopefully your 10 mile run will be cooler ..

Hi Mike,

The aux fan only runs when the key in the ignition is in the on position. and then only when one of two conditions are met. There is a thermo relay on top of your engine, in the water jacket, when it senses temps of approx. 100 degrees C, it will cut on the aux fan. Also there is a pressure switch mounted on the receiver drier for your ac. when ac pressure builds, it turns on the aux fan. IF you motor is running hot, it would help to determine when, as in only when sitting at idle, or when moving down the rode at speed. If it's hot at speed, I would check that t-stat. If it is hot at idle, with the ac off, check that temp sensor, it may not be turning on the aux fan early enough. Or of course it could be both(lol).

Good luck

Thermostat is where I'm looking. The car is getting warm at highway speed. This first manifested itself during my desert trip, and I wrote it off to the desert temps. Now that it is still warming up at home I will be replacing the T-stat before it decides to get hot.

Thank for verifying when the aux fan should run, looks like everything is OK there

Replaced the T-stat today, and diluted my 50/50 mix.

After diluting the mix by ~1/3 (one gallon purified water), and replacing the t-stat, the 10 miles highway run was about 190F in the afternoon heat. Best part was, instead of the temp climbing after exiting the highway and stopping for the light, the temp dropped. Made to run up at 80 and back at 85, and the temp gauge never hit the hash mark between 175F and max.

Not sure if the problem was in the mix or the t-stat, but seems to be good now. Might also have been an air pocket in the water jacket that didn't get burped originally. The old t-stat was dated 1/95, so it very well could have been in there for 6+ years.

While checking for leaks, I also checked the visco fan. At appox 2500 RPM (by ear) the fan disengaged. For those who don't know what to listen for, listen for quiet (sure beats trying to grab the bugger). You'll know what I mean, as soon as you hear the fan disengage. As the engine speed dropped, I could clearly hear the fan re-engage.

I will be watching fopr the next few days to see how well it handles the heat of the day (we're in a desert like heat wave right now).