Radiator fan power draw on highway?

[EcoCivic]

Originally Posted by Piotrsko

Logically it's easy to do this automatically using common stuff. Attach an A/C thermostat, preferably old style manual, and use the ac side which operates backwards: when its hot the system switches on. Bit of experimentation to do the high point setting, but a pair of needle nose pliers works wonders and it will sink 20 amps through the mercury switch and it's adjustable through 50 degrees. The other direction is the hot water heater controller on the radiator I mentioned but it's a bit insensitive and somewhat non repeatable.

Those are good suggestions. The problem is that my goal is to disable the fans based on speed (perhaps over 50 MPH or so) rather than temperature, which the car already does.

The problem I'm having is that the fans come on with the AC compressor even while driving down the highway when they aren't needed. What I would like to do is install some type of device that automatically disables the fans on the highway and allows them to operate as normal at idle and at lower speeds.

[ksa8907]

Originally Posted by EcoCivic

Those are good suggestions. The problem is that my goal is to disable the fans based on speed (perhaps over 50 MPH or so) rather than temperature, which the car already does.

The problem I'm having is that the fans come on with the AC compressor even while driving down the highway when they aren't needed. What I would like to do is install some type of device that automatically disables the fans on the highway and allows them to operate as normal at idle and at lower speeds.

What if you're in a situation where you have high load on the engine above 50mph and the temperature gets too high? Perhaps some kind of mechanical issue.

I think you're wasting your time to be completely honest. You're trying to eliminate the waste of an inefficient alternator by changing the operating schema of your cooling fans....

[EcoCivic]

Originally Posted by ksa8907

What if you're in a situation where you have high load on the engine above 50mph and the temperature gets too high? Perhaps some kind of mechanical issue.

I think you're wasting your time to be completely honest. You're trying to eliminate the waste of an inefficient alternator by changing the operating schema of your cooling fans....

Good thoughts. I'm not sure that running the fans on the highway would help if the engine is running hot. When I had my thermostat out a couple years ago, I experimented a couple times with turning the fans on while driving down the highway at speeds I don't remember, probably around 60 MPH. Whether the fans were powered or not really didn't seem to make any difference to the coolant temp, perhaps because I have my radiator ducted in so any air that passes through the grill is forced through the rad and can't escape around it. However, I now have a different fan setup with a custom shroud, so I may test at what speed running the fans no longer helps cooling anymore as I have wondered about that too.

There isn't really any practical way for me to significantly improve the alternator's efficiency, so not using it where possible and reducing the load on it when I do need to use it is the next best thing I can do. It seems that since the fans are one of the largest power draws on the car, not running them when there is no benefit to doing so would be a good way to accomplish the goal of reducing the amount of power the alternator wastes.

[Isaac Zachary]

Originally Posted by EcoCivic

Good thoughts. I'm not sure that running the fans on the highway would help if the engine is running hot. When I had my thermostat out a couple years ago, I experimented a couple times with turning the fans on while driving down the highway at speeds I don't remember, probably around 60 MPH. Whether the fans were powered or not really didn't seem to make any difference to the coolant temp, perhaps because I have my radiator ducted in so any air that passes through the grill is forced through the rad and can't escape around it. However, I now have a different fan setup with a custom shroud, so I may test at what speed running the fans no longer helps cooling anymore as I have wondered about that too.

There isn't really any practical way for me to significantly improve the alternator's efficiency, so not using it where possible and reducing the load on it when I do need to use it is the next best thing I can do. It seems that since the fans are one of the largest power draws on the car, not running them when there is no benefit to doing so would be a good way to accomplish the goal of reducing the amount of power the alternator wastes.

I've noticed cooling fans playing an effect going up a steep mountain pass at highway speeds, at lest at speeds up to 45mph. I couldn't really go much faster in my Golf diesel, the last car I had the fan go out while driving up a mountain pass. I kept going, it was about 50-60°F outside, and the needle got a bit too close for comfort to the red line by the time I got to the top of the pass.

When the fan got covered by loose firewall material on the Super Beetle going up a hill at 65mph that made for a quick engine failure.

[EcoCivic]

Originally Posted by Isaac Zachary

I've noticed cooling fans playing an effect going up a steep mountain pass at highway speeds, at lest at speeds up to 45mph. I couldn't really go much faster in my Golf diesel, the last car I had the fan go out while driving up a mountain pass. I kept going, it was about 50-60°F outside, and the needle got a bit too close for comfort to the red line by the time I got to the top of the pass.

When the fan got covered by loose firewall material on the Super Beetle going up a hill at 65mph that made for a quick engine failure.

Thanks for sharing. I never would have thought a fan failure would make such a difference going 45 MPH, especially on such a cool day. Everything I could find says that electric radiator fans are typically outflowed by ram air at speeds of over somewhere between 20 and 40 MPH, although obviously this would depend on the design of the vehicle and how powerful the fans are, so the only way to know for sure is to test it.

I think one of the biggest factor is how well the radiator is ducted in. A radiator with large gaps around it that allow a significant amount of ram air to go over or around the rad rather than through it like how my car came would surely rely a bit more on the fans than a vehicle with a radiator that's properly ducted to the grill so all air is forced through the rad and can not bypass it like how my radiator is now. Ever since I ducted my radiator, I noticed that the fans don't seem to run as much in traffic.

[Isaac Zachary]

Originally Posted by EcoCivic

Thanks for sharing. I never would have thought a fan failure would make such a difference going 45 MPH, especially on such a cool day. Everything I could find says that electric radiator fans are typically outflowed by ram air at speeds of over somewhere between 20 and 40 MPH, although obviously this would depend on the design of the vehicle and how powerful the fans are, so the only way to know for sure is to test it.

I think one of the biggest factor is how well the radiator is ducted in. A radiator with large gaps around it that allow a significant amount of ram air to go over or around the rad rather than through it like how my car came would surely rely a bit more on the fans than a vehicle with a radiator that's properly ducted to the grill so all air is forced through the rad and can not bypass it like how my radiator is now. Ever since I ducted my radiator, I noticed that the fans don't seem to run as much in traffic.

This was an 1984 model, so not very well ducted. Plus who knows how many times the radiator had been flushed, or the effects of the fins getting bent over the years. Add to that the 12,000ft altitude and lack of air to cool. All that plus floored and wound up for several minutes, plus the fact I was going slower than 45mph at the very top, the place where it got even closer to the red line. But at any rate, I didn't have any overheating problems as long as the fan was working properly.

[aerohead]

Originally Posted by Isaac Zachary

I've noticed cooling fans playing an effect going up a steep mountain pass at highway speeds, at lest at speeds up to 45mph. I couldn't really go much faster in my Golf diesel, the last car I had the fan go out while driving up a mountain pass. I kept going, it was about 50-60°F outside, and the needle got a bit too close for comfort to the red line by the time I got to the top of the pass.

When the fan got covered by loose firewall material on the Super Beetle going up a hill at 65mph that made for a quick engine failure.

One option is to put the HVAC controls to full heat, full outside air, blower on HIGH, lower both front windows all the way, and cross your fingers.

[EcoCivic]

Originally Posted by aerohead

One option is to put the HVAC controls to full heat, full outside air, blower on HIGH, lower both front windows all the way, and cross your fingers.

Yup that method works well, I've done that before. When I was younger, my aunt had a Mercury Tracer with a burned out radiator fan. She was too cheap to fix it, so she just ran the heater on maximum while sitting in Chicago rush hour traffic. It never got dangerously hot as long as the heater was running on maximum. She drove that car around that way for years trouble free, but it sure wasn't comfortable!

[EcoCivic]

It would seem that on my Civic, ram air at 35-40 MPH is totally adequate for engine cooling even under a sustained heavy load. When I towed my other Civic home through the mountains yesterday, I intentionally left the fans off on the highway to see how well it would cool under load with just ram air. Usually the coolant temp didn't increase at all while climbing, the hottest it got was 193 with an oil temp of 199 and that was towing up 3 miles of constant 6% grade in 2nd gear at 35-40 MPH with the fans off in 90+ degree weather, which is outstanding in my opinion.

So while I can not say that running the fans at those speeds doesn't increase airflow at all, I can say that it cooled great with just ram air at 35-40 MPH under the worst case scenario my car (and most other Civics) will ever see. I do use my Civic for towing occasionally, but not usually much over 1K lbs and it's reasonably flat here in the Memphis area so that type of usage is not at all the norm for this car.

[EcoCivic]

I think I finally figured out a solution. In Kpro, I believe I can set a speed for nitrous to activate at. If I connect a normally closed relay inline with the ECU's fan activation wire and activate it with the ECU's nitrous output set to come on at 35 MPH minimum with minimum RPM, load, and throttle position set to 0, I think that should do it. I plan to get Kpro as soon as I can anyways, so this seems like a simple solution. I'm still trying to think of a way to make this work with a stock ECU though.