I've got a quick question I really need an answer to! I just got (about 3 hours ago) a 1992 corvette lt1 coupe. I have been dreaming about getting another one for about the past 4 and a half years since I had to sell my '87 coupe due to getting married and having a baby. I am extremely excited about it and it is exactly what i was looking for. But, i've got a question. After I got it, I drove it for an hour or two w/no problem at all. When i got it home and sitting in my driveway, i turned the a/c and radio off and just let it sit running for a little while to listen to the motor purring. After a few minutes i noticed the fan wasn't coming on and the temperature gauge was still going up and up. I wasn't too worried at first b/c i remembered my old 87's l98 used to get up pretty high before the fan came on. But as I waited, the gauge got to within about a millimeter of the crosshatched area near the 260 number. I knew something wasn't right then so I turned the a/c on and that fan kicked on, and slowly the temperature of the motor started going back down. My question, is what temperature is the primary cooling fan supposed to kick on at? I couldn't tell if both fans came on or only one b/c it was dark and I had no flashlight, but the top driver's side one def. came on. Any help or advise would be greatly appreciated!!!

Thanks!

 

What does the digital temp gauge read? When I first got my '96 I was worried about the same thing. It seems that the analog gauge does not have a very accurate scale to it. When viewing the digital gauge the fan will kick on around 227.

 

I think the primary fan comes on at 228*. The secondary at 236* or any temp when the A/C is running. As RollaMo said the digital is more accurate then the analog. You can pick up a laser temp gauge at Sears to check the actual temp.

 

My 95 had this sort of same problem. When the a/c is running the fan will cut on. These LT1 were designed to get hot by GM. Mine would run around 200 driving down the road and go to about 240 before the fan kicked it at idle. This got me worried because I never had a vehicle to run over 200. Knowing nothing was wrong with the fans I replaced the thermostat (180)and now it is 190 driving and still clmbs when at idle. I don't worry too much about anymore, I just watch it at idle and never leave the car while idling.

 

 

I bought my 94 about 5 months ago and the first time I sat in traffic (in the winter) I noticed the same thing. After doing some research on this site and elsewhere I found that the LT1 was designed to run at higher temp. You'll find this type of information throughout the forum.

I started monitoring the digital readout and, as others here have already said, it seems to consistently read lower than what the analog indicates. I have to believe that digital readout is exactly the temperature the ECM is reading, and since the fan (both fans actually) is turned on by the ECM and not a preset thermal switch, such as those in most older cars, that digital figure is all that really matters.

I researched my 1994 and found that the fan start temperatures can be adjusted using a programmer; I've not yet pursued this avenue myself, but I am considering it.

 

Thanks for the replies! I took it to my father-in-law's show this morning and we used his laser temp gauge to read the temp on the water pump and heads. He has a snap-on computer so we hooked it up to see what the computer was reading in relation to the guages. We've tracked it down to a faulty coolant temperature sensor. We let the car sit for quite awhile and the car was getting considerably hotter (20-30 degrees) using the laser temp guage than the computer was showing, but was about in line w/the analog guage in the car. (i didn't even think about looking at the digital gauge.) We unplugged the coolant temperature sensor and the inside gauge stayed the same, but the snap-on was showing the computer was now getting a reading of about -38F. So, to make a long story short, we're fairly sure that it's just a bad sensor, not telling the computer the correct temperature. Again, thanks for the replies!

 

I'm pretty sure main fan specs are 217 - 219; secondary 226 - 228 for the LT motors or 150 psi from the a/c pressure sensor.

Unplugging the Temp Sensor and getting minus 38 degrees is a normal result (and if the engine is running, that should generate a 15) Jumper the pins and it should read 300 degrees (and generate a 14). Better test of the sensor is to simply buy another one ($9) and compare it's resistance to the one in your Vette after it's sat overnight - should be close.

If the Temp Sensor is good and the wiring checks out - should have 5 volts on the Yellow wire with the sensor unpluged - and the fans don't come on within specs, the PCM is bad. I'd take another scan while seeing what the fans do. You can check the analog gage by unplugging it from the sender - right head. Should read Lo. Grounding the lead to the Block should peg it at max.

 

My 1990 L98 does the same thing -- driveing its ok and sitting in traffic it climbs right to 260. I just got the car running again after a flywheel change and before it starts to get hot in ct. I would like to figure this thing out. Any help with trouble shooting would be greatly appreciated. PS talk to me like Im stupid because the old hot rods did not have all this computer junk. Thanks guys--Walter

 

Based upon the excellent info you've provided, I think you'll find that replacing the digital temp sensor will indeed resolve your fan-on problem. Sounds like you guys did a good job of troubleshooting this one.

Be well,

SJW

 

The analog guage sensor is located near the manifold, so it will read higher than the Digital guage. The digital sensor measures at the water pump and is what the PCM uses to guage when to turn on the fan. I had the digital sensor go out on my 92 and it kept displaying a constant temp. (127 degrees, I think) The fan never came on except when i turned on the A/C.

 

I have a 84,w a/c,and we know that most Corvettes are "Bottom Feeders",meaning they are drawing air from the bottom,off the hot road,and not drawing from direct grille access. The air has a long way to travel before it gets to your radiator,so I decided to add a after market fan,[17in],in front of the radiator,thinking this helps move the air thru the channel and into the engine compartment faster.It worked,in traffic it didn't heat up as fast,but creaped up a lot slower. Another thing I'm looking at is how to remove the hot air from the engine compartment faster.I noticed when I picked up my hood,w/the motor running,the temp went down a lot faster,due to more discharge space.It dosen't make sense to me that the fan is blowing hot air from the rad,onto a hot motor,and then at the fire wall. The exhaust manifolds give off a ton of heat also;do you think wrapping them helps?

 

Now that I have that problem taken care of, I have found something else I would like some advise on, but I'd hate to start a new thread just for this. My air conditioner is only blowing on the windshield and a little on your feet, and even less out the face vents. It's a digital unit, and my first guess on a regular one would be a vacuum line, but does anyone think it could possibly have something to do w/the digital climate control head unit? The thing works perfectly as far as hot air, cold air, and turning the fans on and off, but it just won't blow the air in the right direction. What does everybody think the most likely culprit could be?

Thanks in advance!


(1992 lt1 coupe, automatic, completely stock, 141k miles)

 

Surprised your Vette or any electronic fuel injected car would run right with a bum coolant temp sensor. The PCM uses that signal to control fuel delivery; ie, it does more than just providing signals for the Digital Temp Readout or fan control.

Your on the right track suspecting a vacuum line. It runs from the source to a check valve under the fuel rail covers. That valve is a good place to check first as it's plastic and prone to failure. If that's not it, vacuum is directed to the HVAC solenoids via the Programmer. A mini processor above and to the right of the accelerator. The Programmer gets it's signals from the Dash via a Serial Data Line. Best to troubleshoot it with a Bi Directional Scanner through the CCM link, though I'm sure you will probably find your problem at the Check Valve.

 

You were absolutely right about the check valve. I checked it today and sure enough it was bad. A trip to the parts store and $5 dollars ended up fixing the whole vent problem. If it wasn't for the people on this board, I would have probably spent 3 or 4 hours today checking every line in the dash. Thanks!

 

On my 1990 I have a dial temp. gauge in the car, what is this digital gauge there talking about in these treads?