1986 Cooling Fan Switch
Thread Starter
Burning Brakes
Joined: Oct 2010
Posts: 1,037
Likes: 28
From: Montclair New Jersey
1986 Cooling Fan Switch
I purchased a fan switch from corvette central. The switch is supposed to turn the fans on at 195 degrees. I changed the sending unit located between 1 and 3 cyclinder. The aux. fan comes on at 195 but the main fan still comes on at 215-220. Did I miss something?? Is there another sending unit?
Thanks....
Thanks....
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
That switch controls when the aux fan comes on. The main fan is controlled by the computer. If you want the main fan to come on at a lower temperature then you have the following options:
1. change the chip in the computer
2. make modifications so that the main fan is controlled by the auxiliary switch
3. Add a manual switch inside the car that allows you to control the main fan.
There may be other options that other members might recommend. These are the most common.
1. change the chip in the computer
2. make modifications so that the main fan is controlled by the auxiliary switch
3. Add a manual switch inside the car that allows you to control the main fan.
There may be other options that other members might recommend. These are the most common.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The main fan is programmed to come on at 228F and the aux fan OEM switch turns the aux fan on at 238 F. These temperatures are completely safe and you should have no concern. GM says to shut the engine off at 260 F and let it cool down. I doubt you will ever see 260. Even 260 is not harmful, but 50% antifreeze at 15 psi boils at 265 F and when boiling is a poor conductor of heat and you can have cylinder head problems. If you keep the 195 OEM thermostat, your new aux fan switch will be running that fan all the time which is not a good thing. I recommend you leave your cooling system alone, it is working just like GM designed it. I have 240k miles on my 87 with the stock cooling system and I have had no problems with cooling and I drive it every day.
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
something i did cause I now live where the summer temps. hit 110+, was to install a all alluminun two row radiator and a dewitts 2300+ cfm fan.Engine now stays around 185-196 on the road, never over 200 sitting, and cools down quickly when i get moving. My next upgrade is going to be a 18" Mark V111 fan in a dewitts fan adapter that they were kind enough to sell . It pulls 3000cfm on low and over 4000cfm on high, I'm doing a tech thread when its done. My point of this is that its your car, an old school person like my self, like a engine to run in the 180-200 range, others have their own way of doing things, none are wrong, just personal preference.
Last edited by oldalaskaman; Jul 2, 2011 at 09:30 AM.
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
Replace the Man switch shown in diagram below with wire;
when new Aux switch closes it will turn on both fans
Investing in the factory service manual set with wiring diagrams is a good investment
Last edited by vetteoz; Jul 2, 2011 at 01:39 AM.
Instructor
Joined: May 2001
Posts: 186
Likes: 0
From: Midwest
This was touched on previously here but if you make a mod to lower your fan on temps, make sure that your thermostat is at least 15-20 deg colder then the fan temp control device. The sensor, switch and thermostat are mechanical devices that are not precise and change with age, or the fan could be running to often with a closed thermostat. Cooling fans, especially two running at a time, require a fair share of engine power (fuel) which we may want to put into the equation as to how cool we want to run. If you have a scanner, watch your idle air control counts step up to maintain the engine's idle RPM as each fan turns on.
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Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
the front fan is pretty much useless , looks like in that drawing that it and the thermo switch that controls it are being used as a control for the main fan, a nice simple way to do it with out reinventing the wheel.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
The fans are staggered for a reason. When you turn both fans on at 195* on a L98, the thermostat is just opening fully. If they both come on then you will likely start the thermostat to close, gaining nothing. You also cause an unnecessary heavy draw on the charging system causing the alternator to work harder. There is no reason I can think of to try to hold a L98 engine below 225*. Also at higher speeds the aux. fan actually can block air flow.
If you must turn the aux fan on at 195* don't turn on the main fan as well. Let it come on at 225*, 228*, or whatever the ECM is set on.
If you must turn the aux fan on at 195* don't turn on the main fan as well. Let it come on at 225*, 228*, or whatever the ECM is set on.
Thread Starter
Burning Brakes
Joined: Oct 2010
Posts: 1,037
Likes: 28
From: Montclair New Jersey
I am going to change the radiator but; I am going to leave the aux fan to go on at 195. I am also getting a bigger dewitt fan. The main fan will go on when the ecm tells it to.
thanks again...
thanks again...
Pro
Joined: Jan 2011
Posts: 580
Likes: 8
From: Clemson SC
Does anyone know how the flowrate from the main fan compares to the aux fan? Seems lke that would be important for anyone making fan operation or replacement decsisions.
I assume the main fan is the one closest to the engine. Is that right?
I assume the main fan is the one closest to the engine. Is that right?
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
the main fan is closest to the engine, its more than enough in most situations, read some where that it flows 1400cfm or so. the higher temps these operate at was a tradeoff to help fuel burn more completely and aid in emmisions control. the aux fan is the one in front of the radiator, i'd guess the flow at bout 800-1000 its bout 6" from the radiator, I added one to my 87 and didnt notice any difference. I then upgraded to a dewitts 2300+ high flow and noticed a big improvement but not as much as I wanted for 100+ temps. still runnin in the 195-220 range. Added a 2 row radiator and got to the 185-195 temps that old guys like me like to see. you can go on and on with this and any other 'upgrades' that you have the abilities to do. as I've said before, there isnt a wrong way, just personal preference. I do believe that runnin the higher temps, and not keeping up on the maint./oil changes/etc. will lead to shorter life for an engine. its why i also went to a 7 quart oil pan, renewed all the bearings/gaskets and started using a high quality engine oil. BTW, I also did these and other improvements that are in the works to my tow truck. hope this helps.,
Last edited by oldalaskaman; Jul 3, 2011 at 07:38 PM.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
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From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
What I did was to use a 180 thermostat, and use the main fan power to control the aux fan relay coil. That way, the extra load on the main fan relay is only 1/10th of an amp. Then the aux relay contacts can go straight to the battery through a fuse. Use a 25 amp fuse on a 30 amp fuse holder and it will be just fine. I have been using this for a long time now.
Remember, the aux fan cools the A/C condenser which keeps YOU cool. It does nothing for the engine.
On my wife's tahoe, I added an electric fan that was tied to her brake light switch. Now, when she comes to a stop, the aux fan cools the condenser when the car is not moving. Her A/C never misses a beat even in 120 degree heat.
When she lets off the brake, the aux fan free wheels.
Remember, the aux fan cools the A/C condenser which keeps YOU cool. It does nothing for the engine.
On my wife's tahoe, I added an electric fan that was tied to her brake light switch. Now, when she comes to a stop, the aux fan cools the condenser when the car is not moving. Her A/C never misses a beat even in 120 degree heat.
When she lets off the brake, the aux fan free wheels.
Instructor
Joined: Mar 2010
Posts: 163
Likes: 0
From: Birmingham Alabama
If I remember correctly, which no one else has picked up on, so I may be wrong, but isn't the sender unit between 1-2 cylinders for the gauge?, and fan sender unit is between 6-8?.
Sara Lou
Sara Lou