Hey guys, got a little situation.
My high speed fans are not going on, temp got to about 235 last night and only the low speed fan came on (I could only see the one on passenger side spinning, can’t tell if the driver side is spinning) usually I can tell when the high speed are on because they are much louder. I checked the underhood relays and even swapped out for new ones and no change. Could it be that the actual Fan went bad? And how can I tell?

 

So did it max at 235 and drop to 225 and did it do that on a regular?

 

Here are the STOCK fan settings on a C5
#1 on at 226*
#2 on at 236*
OMG these fans settings are crazy hot--especially on an auto trans
Best fix and the settings i always suggest when doing a tune
1st install a 160* thermostat---( this will not make your engine run 160* but will make it run in the more normal temps from 185 to 195
2nd get a tuner ( even a mail order tune to re set your fans
I always set fans on a C5 with a 160 thermo as such
#1 ON at 200 OFF at 195
#2 ON at 204 OFF at 201
This should make your engine run in the best range 185-200*
You must install a cooler thermo otherwise you will gain no cooling affect
These settings will cool both your engine and auto trans
Also it will cool your underhood temps and lower the timing deducts due to high ECT and IAT temps

 

Do you think it’s maybe the High speed fans that crapped out?

 

I respectfully disagree about the 160 thermostat and I would stay stock temp.

I doubt your second stage fan went out - it probably did not not get hot enough for it to come on . Easiest way to test fans would be a scan tool with output controls that can turn on the fans - or someone with HP tuners - it can turn fans on too.

I put this together recently to help this very situation.

 

it has always run very cool since I owned it 3 years and this just started. On a 70 degree night it runs at 230??!

 

Fun video - where on earth is the exploding engine clip from? Think I need to see the entire video.

 

Here’s wiring diagram... you checked all three fuses?

 

With that additional info, blocked airflow is my best guess. Did you happen to drive thru a bunch of debris that got sucked into the condenser blocking airflow? Clean your radiator and condensor per the vid and report back if you gut a bunch of junk out and if it helped.

 

Nope
High speed fans are just not coming on at all, only low fan

 

So if it is 70 degrees out and you are cruising at 65 mph, it still runs at 230?

 

Yes and only the low speed fan is coming on

 

It should run below 200 degrees easy at 65mph and 70 degrees F outside. Take your Tstat out, put it in a pan of water with an IR gun and see what temp it opens at. That is what I would do next.

 

When I turn AC on only low speed fan goes on

 

If your temps get up to 230 while cruising at 65mph then you definitely have something other than the fan causing problems. Heat index has been well into the 100s here recently and I still get temps under 200 while cruising at interstate speeds

 

Some confusing info in here. There is no low speed or high speed fan. Both fans are always commanded to run together. There is a relay to turn them on and a pair of relays that switches them from series configuration and parallel configuration. In series configuration they run TOGETHER in low speed and in parallel they run TOGETHER at high speed. If one fan was to fail, neither fan would turn on in series mode, low speed (like your old Christmas tree lights when 1 bulb goes out). If one fan fails it will not run in parallel (high speed) but the other fan would run in high speed.

See the schematic... The Green wire turns on the COOL FAN1 RELAY and voltage is supplied to the left fan, the path travels through the Left fan to the COOL FAN 3 RELAY which is not activated so the current goes through the Right fan.

The DK BLU wire is actually mislabelled it should read HIGH SPEED RELAY CTRL, and turns on WITH the green wire signal. Thus all 3 relays are activated. Current flows through the COOL FAN 1 RELAY, the Left fan, through COOL FAN3 RELAY to ground. In parallel, current flows from COOLFAN 2 FUSE 46 through COOL FAN 2 RELAY over to the right cooling fan.

Blown Fuse 49 would cause neither fan to work in low speed mode. In high speed mode blown fuse 49 would cause the left fan to not work. Blown fuse 46 would cause the right fan to not work.


Hopefully this helps clear this up.

 

Regardless of what fan is not turning on or not your highway temps are still to high. The fans are switched off above 35mph because a powered fan will restrict air flow.

 

I concur. And just because you look up in the radiator intake in the bumper and there isnt a McWalmart bag in the way doesn't mean it isnt occluded. 2 years ago I had similar highway temps and used duct tape around my hand to clear out A TON of sand and pine straw and crap and it made a 20 degree difference.

 

In normal operation, the fans do not run when the vehicle is above 35 mph. Check post #2 in the series below:

https://www.corvetteforum.com/forums...iator-fan.html

If your engine is running 230 degrees at highway speeds, the fans have nothing to do with that condition. They are programmed off. It is more likely that a plugged radiator and or AC condenser in front of the radiator is causing the problem.

An exception might be if the cooling system on your car has been opened or drained recently and before that action, temperatures were much lower. In that case I would suspect that the heads were not properly purged of air using the Factory Service Manual method or other methods discussed in this forum.

 

Drove it tonight, stayed around 190 until I was at a light then it went 235, high speed fans are not coming on at all, just low speed fans