What mph are the cooling fans supposed to cut off at?

95 LT1. Just curious since i thought i heard my fans running while going about 25mph today. may be my imagination lol

Thanks

fans come on/off due to the engine temp.,has nothing to do w/ mph.

I believe 35mph and faster they are supposed to cut off.

I just looked at a couple of bin files, one is set to 0mph, one is 15mph and 2 are set to 65mph.

fans come on/off due to the engine temp.,has nothing to do w/ mph.


correct. It has nothing to do with your speed.

correct. It has nothing to do with your speed.
I thought they cut off after a certain speed... I thought this because when someone tries to give the excuse of having the air turned on while racing people have commented it's supposed to turn off at WOT / a certain speed and wouldn't have effected anything?? :confused:

I thought they cut off after a certain speed... I thought this because when someone tries to give the excuse of having the air turned on while racing people have commented it's supposed to turn off at WOT / a certain speed and wouldn't have effected anything?? :confused:


The A/C compressor will disengage past 2/3 throttle. The radiator fan is unafffected. Our cars have 2 fans and one comes on with the A/C. It is possible that if you have the A/C on and hit 2/3 throttle that the A/C fan may shut off as well as the compressor. I've never made an effort to see if it did, but even if it did the main cooling fan would still function if coolant temp was high enough to trigger it.

The 1 fan works on a thermostat, the other comes on with the A/C.

The 1 fan works on a thermostat, the other comes on with the A/C.

Is this true for all 4th gen cars? Which fan is the fan for thr A/C unit? Drivers side or passenger?

Is this true for all 4th gen cars? Which fan is the fan for thr A/C unit? Drivers side or passenger?


Hmm... I'd go start mine and tell ya, but the throttle body is torn down for a cleaning at the moment. :(

I have to agree with Zepher on this.....

At a certain speed, your fans will turn off.

ex: on the highway, there is no need for your electric fans to be on, you get plenty of air from the movement of the car.

I have to agree with Zepher on this.....

At a certain speed, your fans will turn off.

ex: on the highway, there is no need for your electric fans to be on, you get plenty of air from the movement of the car.

You can agree with him if you want to, but you'd be wrong. ;)

If the motor reaches 220F the fans will turn on no matter how fast you are going. Typically at highway speed there is enough air movement through the radiator that it doesnt get that hot, so they rarely come on, but IF ti got hot enough, they would.

There is no mechanism in the PCM to completely shut off the fans a at predetermined speed.

hmmm....wheres Ion (madwolf) when you need him?

Hmmm... i know the fans are entirely thermostat controlled or commanded on with the AC. The stock fans in a 95-up f-body have three relays, IIRC. One for low speed (of both fans), one for high speed, and one for when the AC is turned on. The pre-95s are set up where the fans have only one speed.... under light cooling needs, one fan is turned on. When higher temps are hit, the other fan is turned on also. i remember this much about them.

But, I thought i saw somewhere that when a certain speed is reached, the entire circuit is cut off so the fans won't be running at highway speeds. Could be mistaken though.

Shoebox? Madwolf?

If the a/c head pressures reach a certain threshold the fans will turn off above a certain speed. I don't think the a/c pressure criteria overrides engine temp criteria.

If the a/c head pressures reach a certain threshold the fans will turn off above a certain speed. I don't think the a/c pressure criteria overrides engine temp criteria.

So, when the motor gets hot, it will turn on the cooling fan no matter how fast you are going.

I had no idea that the A/C fan would turn off at speed if it had a certain head pressure. Live and learn. :o


so, the A/C fan can turn off at speed, but the other one will not be affected. It looks like we were all sorta right, and sorta wrong!? ;) :p

Thanks Rob :bow:

Umm.. Can someone tell me why MECHANICAL fans disengage at high speeds, and these electric ones "don't"?

Where the hell is the logic behind this? Electric fans would be easier to turn off (electrical means vs mechanical), so why wouldn't they?

It only makes sense that they'd shut off. at high speeds, the wind could turn the electric fans faster than they would turn normally, when on... so the fans should just freewheel. You don' need them at that point.

if your at idle and head pressure of the AC system hits 250 PSI your fans WILL come on. If your driving 95MPH and your head pressure reaches 250PSI your fans WILL come on. If your sitting at idle and your temps reaches normal fan operation the fans WILL come on. If you are driving 95MPH and the temps reach normal fan operation the fans WILL come on.


ex: on the highway, there is no need for your electric fans to be on, you get plenty of air from the movement of the car.


It doesn't cut off because your going fast enough. it cuts off beacuse the cool air entering the radiator is enough to keep both the head pressure under 250 and the ECT happy. It should not be effected by MPH. Thats not an imput anywhere into the fan control systems that I have ever found.

It doesn't cut off because your going fast enough. it cuts off beacuse the cool air entering the radiator is enough to keep both the head pressure under 250 and the ECT happy. It should not be effected by MPH. Thats not an imput anywhere into the fan control systems that I have ever found.

That is what I was saying from the begining and everyone disagred with me. :confused:

Probably just from the wording. You can not jugde a pressure and temp drop in the radiator and condensor based on MPH. id doesn't really have a thing to do with it. It's just the simple dynamic of the air entering teh radiiator. Not hoe fast you are going.

The fans are supposed to cut off at speed so as to not impede the flow over the radiator.

here is a screen shot I took of the program,
http://www.transamws6.com/pics/fans_cats.jpg

The fans are supposed to cut off at speed so as to not impede the flow over the radiator.

here is a screen shot I took of the program,
http://www.transamws6.com/pics/fans_cats.jpg

According to the explanation of any of the constants values in the programming, I don't see anything that tells the fans to cut off at a certain speed.

If you are going to say it is the "Fan Threshold High Speed (MPH)" , the help says:
"This is the vehicle speed threshold above which the High MPH coolant temperature fan thresholds are used to control the fans. For speeds less than this value, the low MPH thresholds are used."

So, it is just the division between when the high and low speed thresholds (Low MPH and High MPH) are used in the previous constants.

here is what the TPI cars have the setting as,
http://www.transamws6.com/pics/fans.jpg

Fan 2 has the settings at 255 since the ECM has no direct control of the secondary fan on the TPI setup.