So today i was driving home with the ac cranking, the temp outside was prob about 85 but 100% humidity, and i noticed that my temp wqas going higher then ive seen before it got up to 253 at idle? so i checkd my auxillary fan and it was not on? so i got my infared thermometer and took readings at the base( near motor) of the top and lower radiator hoses, bot were the same at around 190-200? now my question is... is there a separate sensor for the guage inside the car? as apposed to the one that turns on the fan? My ac was blowing colder than ever and the car seemed to be running great? and i think i have to go with the temp of my hoses compared to the guage in the car. So could it be a faulty sesnor? how many sensors are there? where are they located? Thanks

 

And my main cooling fan is cranking!

 

The sensor between cylinders #1 and #3 runs the aux fan and the sensor between cylinders #6 and #8 runs the gauge on my car.

 

on an 89 the one between 1 & 3 is a temp switch and turns on the pusher in front of the radiator. The one between 6 & 8 is a sensor that informs the computer of the temp which turns on the puller fan between the engine and radiator. pusher turns on at aprox 238* and the puller is programed to turn on at 228* unless the air is running which turns it on automatically

 

Sounds like you have an issue with aux fan operation.

 

'89 specs are 226 primary; 228 Aux. That's with the a/c off. The Aux Fan, if it's right, should never come on (plenty of Vettes left the Factory without this option so it's basically useless until the cooling system mucks up, at which point it's probably going to boil over anyway). With the a/c on, the ECM drives the Main Fan Relay when the Pressure Sensor Switch on the High Pressure Line opens and it should do that at about 220 psi. The contacts should close at 170 to 190 psi and the Fan should turn off (assuming CTS signal is below 226 degrees). The gage sending unit - basically a thermistor in that it's resistance decreases the hotter it gets) for the gage is between 6 and 8 on the right head. Disconnect it and your temp gage should read Low (max resistance). Ground the wire and it should read max (around 300 - No resistance). Otherwise, do what every Service Manual tells you to do - scan it so that you can see the Coolant Temp Sensor Signal and compare it to the gage to verify the gage's accuracy (generally no more than a 5 degree difference) and at the same time, see if the main fan is being driven when the Sensor Signal is at 226. To test the a/c side, you need to hook up a manifold gage set so that you can see what the pressure is when the fan comes on and goes off. If you want to test the aux fan, block air flow, keep the a/c off, and while observing the Coolant Temp Sensor on the scanner (it's really hard to know what it's doing if you're sitting inside looking at the Dash) you can sometimes get it warm enough to reach it's threshold.

 

First off, you should aim the temp gun on the cylinder heads to see if it is really overheating. If they are lower than "253 degrees", then chances are either the wiring or sensor is bad. Back when I had my digital dash, I saw 299 degrees, but in reality, it was the sensor that was shorting to the ground.

 

I think my 1989 specs were primary on at 228 aux on at 236 with air off. I put a new sensor/switch on the aux fan that turns it on at 205 according to my digital gauge. That was a solution for any tendency to overheat. You can get one from Mid America Corvette for $15.

 

Every service manual I've seen shows specs at 226/228 (non a/c) - so does my Scanner. Using the Aux fan without upgrading the alternator usually doesn't work - It puts out about 25 amps at idle. Each can consume 10; the a/c another 10 to 15, add the headlights, radio and the voltage starts to drop. The fans slow down and before you know it, it's above the threshold for either fan. These cars did fine from the Factory with one fan and when new, with the a/c on, they ran 205 to 212 around town; at the thermostat on the highway. If yours is not doing that, something else is wrong - usually crud in the coolant passageways (including the heads), blocked air flow, high resistance in the wiring, etc, but that happens with 20 year old cars. It depends on how much you want to put into it to get it back to what it was designed to do.

 

I don't think that is correct. Why would they be set to come on so close together? That is within a sensors margin of error. Also the primary fan now seldom comes on and and I have had no charging problems in 2 years. The pusher fan does the job.

 

My pusher never came on. The puller would drop the temp in a minute or less. I ordered a temp switch to turn the pusher on at 210* and cleaned the mess out from in front the radiator. There was every thing you could think of in there. Now the pusher very seldom comes on. I had to almost force the puller to come on without using the AC. My thought is your gauge is wrong and check for debree in front of radiator.

To test the pusher fan ground the wire on the temp switch between 1 & 3. Fan should turn on. If it doesn't turn on jump the wires at the fan. If it runs the relay is most likely bad, if it doesn't the fan is bad.

 

Wrong.
The ECM gets it's temp readings from the Coolant sensor (CTS ) at front of manifold. Sensor between 6/8 is for gauge only.

 

Beats me - but the "Heavy Duty" Cooling option was basically a marketing tool (as were all the fan kits, including the Temp Switches that are still being pushed today, only in '89 they were among the first items in Mid America's Catalog - and of course I bought one). At the time, little information about Electronic Fuel Injection and Emissions controls were available and the ads played to the prevailing mentality (as some still do) that these cars ran hot and wouldn't last very long or couldn't go as fast without something to keep them cooler. The option cranked up the Sticker by another $100 (with maybe $10 to $15 worth of parts with few warranty concerns because it never came on). The Main Fan, the same as a Vette without the option, dropped the temperature 5 to 10 degrees before cycling off. It's all that was needed and when working as designed, these cars did not have temps above the threshold and they didn't boil over (well not until the head gasket let loose anyway). Running the a/c, which was/is exempt from Fed Emissions, brings the main on sooner and keeps it running longer (it has to if you want frosty air) and the temps are/were even lower. If you don't have a Service Manual, pick one up, though there are some errors in it which were corrected by Service Bulletins. You can find all of the operating parameters in several places. As to the later designs, 2 smaller sucker fans, the engineering was necessitated by the refrigerant changeover, with a gas that will make higher temps (pressures) when it's 90 degrees or better. It has nothing to do with Coolant Temperatures which need to be at the theshold or a few degrees less to meet Emissions. That's why the Toyota in your driveway has the same operating parameters, as do the 1000's of SUV's and Soccer Mom Vans no one wants anymore. And I don't know of many who have tried to make those beasts run any cooler - they don't have digital temp readouts - but I'm sure a few have tinkered with them.

 

My car is the Z51 so the upgraded cooling system was part of the package. It has the aux. fan, oil cooler, and a radiator that is thicker in cross section than standard. I have no cooling problems at all.

 

I don't either and though mine doesn't have the Z51 option, it did come with everything else; ie both fans, HD radiator (which as far as I know, is the only replacement available for those who might want a new OEM radiator). Temps average 205 to 212 in town (I don't turn the a/c off); 195 or the thermostat above 25 mph. I've owned it since new and that's how it left the lot. As mentioned, I tried a Lower Temp Switch and tied both fans together Years ago. And ok, I also bought a throttle body air foil, several exhaust systems, and myriad of hyped up parts that really did very little. It's all in a box somewhere.

 

Thank you for this input can you tell what temp my 89 corvette should be operating at in summer weather with ac on.

 

Been having the same problem with 1989 also. Coolent level is fine, both thermostats working fine , fans working fine but when in slow traffic temp would clime to 250 and i had to shut it off to cool ??? .. But i started looking all over the engine for the problem, guess what I found the problem. The car is 27 years and really clean. So now i started crawling all around and 1/3 to 1/2 of the front of the radiator was covered with light debree and looked like lint and grime and pollon , it has probally been collecting there for years and the only way to see it is by lying in front of the car and looking between the air dam and the lower front. It could actually be pealed off the radiator like a lint tray in a dryer . So now i will blow it out with modest air pressure from the back then the front then i'll do the same thing with a low pressure water sprayer then with a goid soaking with a water hose . But make sure you keep the pressure down so the fins are not dammaged. I'm guessing it has never been cleaned since it was new 27 years ago.
The front of my radiator looked like a lint screen.

Doug