I was in 80 deg temperatures a few days ago in stop and go traffic. I noticed the water temperature on the analog gauges was near the mark of overheating. I didn't think to look at the digital temperature until later when I was finally in moving traffic again. The temperature dropped right down to normal. I thought maybe the relay was bad on the fan(s). To test it, I started the car up and turned on the A/C. Only fan 1 came on. Aren't both fans suppose to come on? I then pulled the connector to fan 2 to test the fan connecting the circuit that the relay would in normal operation. Fan 2 works fine so I am assuming it is the fan 2 relay. I can't figure out how the FSM tests the relay. Any help other than taking out the relay and testing in manual. The FSM says ground CKT 473 but how can I do that with the connector unplugged.

 

I would bet that you have debris blocking your radiator underneath. These cars are notorious for sucking up grass trimmings, leaves and such.

 

I personally wouldn't put a lot of faith in the analog water temp gauge. It's non-linear in that as the temps rise, the distance the needle moves gets shorter.

When I had my 92, I always left the digital display set to coolant temp. It's much more accurate and gives a "real-time" display of coolant temp rise/fall.

C4's will run hotter as that helps to reduce emissions. It's not uncommon for coolant temps on hod days to be in the 195-215 range. This is normal. Your FSM will show what temps will cause the primary and secondary fans to start.

C4's are definitely susceptible to getting dirt and debris in front of the radiator and A/C condensor. Youcan clean junk out with a garden hose pointed at the radiator from behind the fan shroud. Just don't use a lot of water pressure.

One other thing to consider is that as the C4's get more and more miles and years on them, the radiator tubes gradually become thinner due to the flow of coolant through them. As the tubes thin, they lose their ability to effectively transfer heat out of the coolant. The only real cure for that is a new radiator.

Also, if a cooling system flush is not done every few years, it's possible to get some of the tubes blocked up so no coolant flows thru them. Same wit passages in the block, heads, and the various tubes.

 

I had the same issue on my '94. Turned out that I was low on freon. Charged the system(needed about 1 pound), and the secondary fan kicks on with the primary when AC unit turned on.

Others have had this same problem. So it may not be a bad relay.

 

And in addition:

Only one fan comes on when the A/C is turned on the 94 (or at 219*). (95 & 96 are different fan configurations). The secondary fan comes on at 239* as read on the digital readout. Until that temperature, only one fan is on and is usually it is insufficient airflow if stuck in stop and go traffic for a while.

The secondary fan does pull more air than the primary fan but who wants to wait that long. That is why a lot of people including me has put a aux fan switch to start the secondary fan when needed. If I get stuck in traffic and it goes past 215*, on comes the secondary fan.

In regard to your problem it depends how long you were in stop and go. But I would at least change the coolant out, give the radiator a flush and replace the thermostat. The stats do get tired and can restrict flow just enough on border line cooling situations. Make sure to get a LT1 thermostat.

 

The first thing is to flush out between the radiator and the air condition radiator, make sure the fans are running properly. C4 corvettes run as hot as 235/40. I installed a 406 with a big cam and once the temp got above 100, witih the air conditioning on in city traffic, the heat gauge would run up to 240 very quickly. I went through cleaned between the radiators, with a new engine no problem with flow through the block, both fans were coming on. I purchased a fan from a 1997 lincoln mark VIII. Installed the new fan rewired to a 40 amp relay, and the car never gets over 210, never! On the highway 190, in city driving with air on 210. I am an old school guy, and I never get nervous about my temp any more..

 

It was 56 degrees today. Stopped in traffic for about 5 minutes. The digital temperature went up from 200 to 230 degrees before I started moving. I did not have the A/C on. I had it in the shop a couple weeks ago. They put in a new thermostat at that time. This will take some more investigation. The car did set for 4 years so radiator could be getting bad.

Fan 2 will come on if
ECT about 228 degrees
Engine oil temperature above 277 degrees
A/C head pressure above 225 psi

 

I forgot to mention that I looked inbetween the radiator and the A/C condenser and only notice a little trash near the middle top of the radiator.

 

How about switching the relays? That will show tell me if one is not working or not! I am trying that tonight. Thanks for getting the wheels a spinning in my head!

 

The only two quick suggestions I have is to make sure they put in a “LT1” thermostat. And your very possibly right about the radiator. It just may have a reduced flow which is the biggest factor in the cooling system. Also the replacement GM radiators are a bit thicker than the original ones which does help some. I got one and run about 193-195*. In traffic get hotter but never goes to 230.

 

Well, I checked the fan 2 relay with fan 1 connection and it works correctly but I broke off the plastic latch to the connector. Can one just replace the connector? I mean can I push out the wires for the broken one? Gosh, these plastic connectors are sure brittle.

I looked at the radiator again. Yeh, there is a little trash up near the top so it might be worth getting in there a cleaning it up. Is it easy to get the fan shroud off? It looks almost impossible to run air or water on the back side to clean it up.

 

I looked at the receipt and the shop didn't list out the parts (it was a restoration repair shop). Anyway, what is the difference between a regular thermostat and an LT1 thermostat?

 

You can jack up the front end and crawl under and spray between the rad. and condensor. There is also a opening on the passenger side fan shoud that you can spray water through. I agree that these are not as efficient as removing shroud and radiator in order to spray directlry through the fins, but it is better than nothing.

Are you running 50/50 coolant/distilled water ?
Is your expansion tank "full" whwn engine is cold ?

How many miles on your current WP, and have you checked to make sure it is not leaking at the weep hole ?

230* at 80* ambient seems to high. I have never seen higher than 215* at 95* ambient on my '94.

Also, if you remove your top fan shroud, you will need to disconnect the IN/OUT ports to your condensor, so these would be a full AC system recharge procedure...(will require new accumulator since you open system)

 

The repair shop put on a brand new water pump, the system was flushed and new antifreeze was put in (assuming they know it should be 50/50). I doubt they used distilled water. I got new OptiSpark also. They said they put in a new thermostat. Resevoir is at cold mark.

I can try a new thermostat and cleaning out the radiator. It looks like the top shroud will come off without the need to break the A/C lines.

I will watch it more closely the next time I drive it or give it the going over on Saturday.

Any recommendations where to get a new radiator if it comes that? On the farm, we used to just get them rebuilt or is that not an option for this radiator?

 

OK, you checked the overflow reservoir, but did you check the black expansion tank that sits near the windshield on the passenger side ? Most times, after a flush/refill, it takes a couple of days of checking and topping off coolant in the expansion tank.

 

Completely full.

I doubt if it is the new thermostat but I will give that a try. My guess it is the 15 year old radiator.

1) Try to clean out the radiator.
2) Try a new thermostat.
3) New/rebuild radiator.

How does the radiator come out, top or bottom?

 

It comes out from the top. Remove air cleaner, MAF and air duct, upper fan shroud, and then radiator.

 

I can try a new thermostat and cleaning out the radiator. It looks like the top shroud will come off without the need to break the A/C lines.

Take care when removing that radiator shroud. Those 10 mm bolts on the side are a bitch to get to and I actually DID break an A/C line by accident last time I removed mine to clean it.

 

Well, I least I feel a little better. I thought I was the only one that did stuff like that.

 

Still need a couple questions answered?

1) pColt94, what is the difference between a "regular" and a LT1 thermostat?
2) Any recommendation on where to get a new radiator?

I found this one http://www.gmpartsdirect.com/catalog/frameset.cfm for $166.57.