I have an 85 with the 2nd radiator and auxilliary fan. I am in El Paso, so it is already getting up near 100*. I have the main fan wired to run all of the time, because the Chevy mechanic told me the ecm wasn't signaling to start the fan at the right temperature. In town, without the AC, the car runs at 195-205. With the AC turned on the temps climb up past 230, and I start freaking out. I know that that temperature is normal. But here's what concerns me. The car has 200,000 miles on it. When I'm up to speed, the oil pressure is about 55 psi, w/o AC (at the 195-205 temp) and drops to about 40-45 psi when running down the road at 225-235*. At a stop, w/o AC the oil pressure is about 18-20 psi. But, with AC going and up in the 230* range, the oil pressure drops to about 10 psi. That freaks me out. Is evrything OK, all things considered, or do I risk damage with that low of oil pressure? Btw, the engine runs strong, uses about a qt of oil per oil change.

 

Maybe, but probably not, at least for Coolant Temp. Oil Pressure is a function of it's temperature.

Since you don't know if your Display is accurate, I'd start by comparing the Coolant to the Coolant Temp Sensor with a Scanner. They should be within a couple of degrees. I would also replace the ECM as a full time fan doesn't work as well as one that cycles.

A/c operation results in lower coolant temps as the fan is on sooner and runs longer. It needs to because you don't make cold air without keeping what's going on in the Condensor at a considerably lower temp than the what's going on in the Radiator. That's why the Condensor is in front and that's another reason why the coolant temperature is controlled by a thermostat. Since your Vette's Main Cooling Fan is a full time affair (though above 40 mph it's probably impeding air flow), the coolant shouldn't be heating up with the a/c on and that's either a crapped out cooling system (compressor load overwhelms a partially plugged up radiator, bad shroud, missing front spoil, etc) or a plugged up a/c system. Start by checking it's a/c operating pressures. The high side should average about 200 psi and that's normally controlled with the Main Fan cycling on/off between 190 and 230 psi. Check those pressures with a Manifold Gage Set. Running the fan full time will drop the high side too low and that means the compressor is going to cycle which increases wear (and because it's engagement isn't controlled by the ECM for your Year, it can also cause minor idle issues; ie, most of these Years "feel" compressor engagement - better to just keep it running and it does that really well with the fan cycling on/off).

The Aux fan isn't necessary for a/c and isn't linked to it. It was initially a Dealer installed option following complaints from racers and high altitude users. There was extensive hot weather testing of the Vette and a Vette with the single fan was able to maintain appropriate cooling with or without the a/c blasting. Return it to the way it left the Factory and it'll be fine.

 

Thanks for the response. I reread your post I asked a while back about the operating temperatures, and have been considering spending the money to return the ecm, cooling fan to their original operation, but the oil pressure made me wonder if I was throwing good money after bad. After all, it does have 200k miles. But, like I said the engine seems strong. Thanks, again, for your help. I guess I will probably take it to the Chevy dealer and have them put the new ecm in it, and redo the fan set up. Thank you for being patient with me.

 

What oil weight are you using?
My 57 Chevy pickup has a 1980 4 bolt main truck block, and with 5W30 oil, the lifters make noise. With 10W30, the noise is gone. Oil pressure is up about 7 PSI.
Your engine is of the same factory machining tolerances as my truck engine. I would jack up the oil weight a notch in the summer, and thin it out in the winter.
You can remove the air filter and the top of the radiator shroud, and clean out the air cavity between the radiator and the condensor.
Also, on my 86, I wired the main fan power wire to the coil of an auxiliary fan relay, and when the computer calls for the fan, there is more fan capacity than original, and it cools down quickly.

Just a note,
The dealer option will be really expensive. Nobody there knows your car even as well as you do. I would hunt down a corvette mechanic somewhere near where you live. Buy a service manual for your car, and you will discover how easy it is to move the wires back and restore the fan operation.
You can do it easy. The ECM has 2 connectors and plugs in with a "snap". your kid could do it.
Also, with the fan wired on all the time, the engine takes a long time to warm up. That will cause more damage than heat.

 

Well, this is going to hurt when I admit that I just dropped my car off to have them change the plugs and oil, and I don't know what weight they used. I will know better the next time. I have cleaned out the space between the radiators. Your advice on the ECM is really encouraging. I thought it was a real chore to get to it, and then I thought I had to program it. If I could just get it back to the way it came from the factory, I would think that would be really good, and I think the ECM would allow me to do that. Plus, it would keep from wearing out the fan motor to boot.

Thanks again to all of you. I always feel bad that I don't have the ability to help someone as the folks on the forum have helped me. One of the real bonuses I have found by getting my Corvette is that fellow owners here aren't just nice people, they represent more than that. It kind of like family. Pretty danged cool.

 

I would use 10w30 oil in high ambient air temps where you live at too.

BR

 

At 200k, you motor has larger clearances than when new. Oil pressure will be somewhat lower. As mentioned a higher viscosity oil will help. The motor is on borrowed time at this point. Just don't take it out drag racing anytime soon.