nj02vette

Just started a few weeks ago. When driving, the temp is good, but when stopped, the temp climbs up. Coming off a highway and hitting a red light can make the over temp warning come on.

Never had this issue until recently. Before that, temps were rock solid at 220.

Fairly certain I know what the problem is, the radiator fans aren't running. That would explain everything. But how should I diagnose? Had a Camaro a long time ago that had the same behavior but that was the relay that turned the fan on was bad, not the fan itself.

So does anyone have any insight on how the fans are controlled. Temp sensor controlled? Should I start out trying to run the fan motors off 12V to see if they're good, then work backwards or is there a better procedure?

Thanks.

bjones7131

Cut hvac on, this brings the fans on. Otherwise with hvac off they come on at about 226 on low and if temp increases to about 235 fans go to high. Look under bottom of rad and make sure nothing has sucked into rad and plugged it, the vette is a bottom feeder. I am sure others more knowledgeable than i will chime in. My temp numbers maybe off but should be close

pewter99

do a search (yeah I know) there are a few threads going about this now....IF you decided to replace fans the Dewitts SPAL fans rock

65GGvert

I had a similar experience and one of the 30a fuses for the fans in the underhood fuse block was blown.

BigGun

Corvettes have fan relays too. This link will help you get started. http://forums.corvetteforum.com/c5-g...an-relays.html

Nate@VanBortelChevy

Fans are controlled to come on by the PCM. When the engine is warm you can turn the A/C on and while sitting idle the fans should come on. The best way to diagnose would be with a tech-2 or bi-directional scan tool. Command the fans on, check for power/ground at the fan motor connectors. A good preliminary check are the fuses/relays and visually inspect the fans, connector, harness.

BigGun

The engine temp must be at least 185 degrees for the fans to come on.

martysauto

If the ac is working correctly. The coolant fans will run when the ac high side pressure hits about 250 psi. Install a set of gauges and watch what happens. The fans will run because the ac needs them. They will run after a cold start if the ac is on.

nj02vette

Thanks for all the replies. Going to take a look soon but my time is limited.

Don't think the radiator is clogged with anything, because it would overheat all the time, not just when sitting. At speed and the radiator is getting airflow, it is normal temp. AC on/off isn't the culprit. I know the different setpoints. This is abnormal behavior. Something/somewhere is broken.

For those that didn't take a look at the car in sig, it's supercharged with ECS kit. 3 years, temps have been rock steady, even driving in 100°F heat, so I know it's not anything there.

I'll do a quick look at the fuses. Didn't think of that. For everything else, have to put the car up since the radiator is laying different from the stock setup and not as accessable with the blower on top.

Didn't think of that. I have HP Tuners and can command fans on/off.

nj02vette

Awesome schematic. Exactly what I was looking for. This gives me a roadmap on what to test.

When I get a chance, will just wire up 12V to the fans direct and see if they come on. If not, problem found and will replace. If yes, will just move up the line.

k24556

This may help:

The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

Normal driving with driving speed that flows sufficient air across the radiator with the AC off, the coolant temperature with a factory thermostat is 190°F, The fans will be off. The factory setting will not let the first cooling fan come on until the coolant reaches 226°F.

The low speed cooling fans are controlled by the PCM based on the following inputs:

The A/C system
The Engine Coolant Temperature (ECT) sensor
The Vehicle Speed Sensor (VSS)
The PCM will turn the low speed cooling fans ON when any of the following conditions exist at idle:
Certain PCM Diagnostic Trouble Codes (DTCs) are set
ECT above 104°C (219°F) will enable low speed fans
A/C head pressure above 1510 kPa (219 psi)
Once the low speed fans are turned ON by Engine Coolant Temperature, the PCM will turn the fans OFF when that temperature has dropped about 6°C (11°F) . If the low speed cooling fans are turned ON by high A/C head pressure, the PCM will turn the fans OFF when the pressure has dropped to 1034 kPa (150 psi). The minimum ON time for the low speed cooling fans is 50 seconds.
When engine speed is above 3500 RPM for 12 seconds and the engine oil temperature is above 127°C (261 °F), the low speed cooling fans will be turned ON.

HIGH SPEED COOLING FANS

The High Speed Cooling Fans are controlled by the PCM based on the following inputs:
The A/C system
The Engine Coolant Temperature (ECT) sensor
The Vehicle Speed Sensor (VSS)
The PCM will enable high speed cooling for both fans when any of the following conditions exist:
Certain PCM Diagnostic Trouble Codes (DTCs) set
ECT above 109°C (228°F)
A/C head pressure above 1551 kPa (225 psi)
Once the high speed cooling fans are turned ON by the Engine coolant temperature, the PCM will turn the fans OFF when that temperature has dropped about 6°C (11°F) . If the high speed cooling fans are turned ON by high A/C head pressure, the PCM will turn the fans OFF when the pressure has dropped to 1241 kPa (180 psi). The minimum ON time for the high speed cooling fans is 26 seconds.

When driving/ cruising the engine should run close to what the thermostat is rated.

nj02vette

Not the fuses. Will bench test relays.

Need to get my copy of HP Tuners back from a friend. Will just try commanding the fans to come on. That will tell me a lot.