Just got home after a drive. Put the car in the garage and shut down the engine. The engine turned off and stopped cranking. But there was a VERY loud air whooshing noise coming from under the hood. Like a wind tunnel. I stood and waited for a while to see if it would stop, but it didn't. I got in and turned the engine on and off. The whoosh stopped. Hmmmm... That doesn't sound right.

Any engine geeks out there want to help me understand this?

 

Radiator fan?

 

Could be the cooling fans staying on to help cool the engine after shutdown? Did you drive it kind of hard before you put it away?

--C

 

A little bit hard. Not track style. It is a warm day with full sun. Maybe it's just the radiator fan working overtime. I'll watch out for more occurrences and see if/when it happens.

 

check the temp gauges as well. Might be related to what the water temp is at shutdown if it's the radiator cooling fan.

--C

 

Cooling fan staying on for a bit after shutdown.

 

There's the radiator fan that always goes off but a little fan that turns on when the engine is turned off and the engine is over a certain temp. It also turns on when you are in a traffic jam on a hot day when the temp of the engine is really hot. I remember being in a traffic jam and was wondering why my extra fan was not coming on eventually saw my water temp go to redline and then Mt Vesuvious. Yep, my little extra fan was shot. Had a friend with same problem who blew head gasket on a BMW.

 

I appreciate the help.

 

C7 only has one fan.

 

Wow. I thought it was more popular than that!

 

 

My Audi does the same thing. Will check and see if the C7 does it, didn't notice.

 

Once the car is stopped and the fan is running (temp sense switch on), the coolant lies dormant and the coolant in the radiator cools quite quickly (not flowing). The temp sensor is normally on the head and not the radiator (not sure on C7). When you started it again, the water pump moved the lower temperature coolant from the radiator into the engine and triggered the sensor switch to off (now it was below threshold). that's how it normally works and that would be a reason that restarting the car and then shutting it off resulted in the fan not coming back on.

If you would have let the fan run with thecar shut off, the fan would have shut off by itself eventually (1 minute or so usually).

 

Here is the service information on how the C6 handled shutoff and cooling fan operation.

Expect something similar for the C7.


The engine cooling fan is a variable speed fan. The ECM controls the fan speed by sending a pulse width modulated signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal.

Cooling fan speed is effected by many different conditions and can be adjusted from 10% to 90% duty cycle (PWM), 90% is considered high speed fan. When multiple cooling fan speed requests are received the ECM uses the highest cooling fan speed of all the requests. The ECM commands the cooling fan ON under the following conditions:

Cooling fan duty cycle starts when engine coolant temperature reaches approximately 95°C (204°F) and reaches high speed at temperatures above 113°C (235°F).

Cooling fan duty cycle starts when A/C pressure reaches approximately 1100 kPa (160 psi) and reaches high speed at A/C pressures above 2480 kPa (360 psi).

At engine oil temperatures above approximately 150°C (302°F) the cooling fan duty cycle will be commanded to high speed.

At transmission oil temperatures above approximately 132°C (270°F) the cooling fan duty cycle will be commanded to high speed.

After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 113°C (235°F) or the A/C pressure is greater than 1720 kPa (249 psi) the cooling fan duty cycle is set to 50%, low speed. If the coolant temperature drops below 110°C (230°F) and the A/C pressure drops below 1660 kPa (241 psi) the fan will shut OFF.

The fans will automatically shut OFF after 2 min. regardless of coolant temperature.

 

Paul is just a wealth of knowledge.

What a great forum asset!

 

I've never had the C6 fan stay on. But before shut off it always been extremely loud.
You don't even hear the corsa's. Shutting off almost sound like a small turbine
spooling down. Its been this way since new. The BMW and Honda are no
where near this loud.

 

100% Thanks Paul!!

 

I can't imagine your car was that hot at this time of year. Sounds like something continued to run after shut down. The only thing I can think of is with DI there is a high volume pump near the motor I believe, couldn't see why it would make noise after shut down though. Keep an eye on it, not that you need me to tell you that.

 

Thanks Paul. I am really glad to see they are doing a PWM variable speed fan control. It is a far better approach when done correctly. About 6 years ago I had a company (Power Systems Management) that built variable speed fan controllers and pitched the Ford engineers in their headquarters about it. Very similar operation to what they are doing on the Vette, but we had far less info coming from everyday telemetry.

Can you tell me where the coolant temperature sensor is located? I assume it is at the coolant output of the radiator to provide lowest closed loop delay.

 

How about the rear fan, when does that come on? Can dealers or anybody get c7 service manuals on line now. Did you type all that?