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September 2021
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Kirkham Motorsports

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  • 1 Post By moore_rb
  • 1 Post By patrickt
  • 1 Post By Jeff Hamilton

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  #1 (permalink)  
Old 06-13-2021, 07:48 AM
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Default what causes cooling fan relay failure

I have had 2 cooling fan relays fail this year. Getting the fan to start again is as simple as changing the relay which is easy to get to and I now carry a spare but I would like to address the cause. Any ideas?
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Old 06-13-2021, 08:25 AM
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I would say the fan is drawing more current (amps) than the relay is rated for.
If the rating is correct, go to a higher rating.
If you still have problems, try to find a higher quality unit.
The relay should be rated for constant load, not intermittent.
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Old 06-13-2021, 08:32 AM
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Generally, it is three words written on the relay "MADE IN CHINA" and if it is Bosch then your amp rating is to low. I would go to a German car dealer in your area and have the parts department find you a HD unit for one of their top model cars, more than likely they will be Bosch no matter what type car. Or you can contact Texas Industrial Supply at texasindustrialelectric.com/relays and look over their inventory. Look at 0332-002-168, if it were to fail then you have other problems in your system.

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Old 06-13-2021, 08:40 AM
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Heat and vibration-

If the fan is drawing amperage near the relay's upper limits, then the relay is going to get hot while the fan is running. Check the gauge of the feed wires to the fan, and then check to make sure the 12v source, and the ground wire to the relay are both larger gauge wires than the fan feeds. make sure the ground wire is connected too a good, clean chassis ground spot with a solid/unlimited electrical path back to the battery negative...

Inside the relay are a bunch of solder connections- Heat and vibration can cause these solder joints to crack and result in open circuits. When this happens the relay stops working.

I always buy 2 of every relay for my fans and fuel pumps- when one fails, I swap in the spare, and I pop the failed one open, hit the solder joints with a soldering iron, then test it to see if it works. If it does, I pop the cover back on it and put it back with the spare parts... if it still doesn't work after re-soldering, then I toss it and order a new spare.

wash, rinse repeat
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Old 06-13-2021, 03:16 PM
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Quote:
Originally Posted by bkozlow View Post
Generally, it is three words written on the relay "MADE IN CHINA" and if it is Bosch then your amp rating is to low. I would go to a German car dealer in your area and have the parts department find you a HD unit for one of their top model cars, more than likely they will be Bosch no matter what type car. Or you can contact Texas Industrial Supply at texasindustrialelectric.com/relays and look over their inventory. Look at 0332-002-168, if it were to fail then you have other problems in your system.

Bill K
he beat me to it... "made in CHINA" all joking aside you cant simply throw a higher current relay at the problem. If that is the case than you will need to confirm that the size wire/fuse is of the correct size to handle the load of the fan as well or bad things may happen. Better safe than sorry. Sorry I am an electrician by trade.
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Old 06-13-2021, 06:17 PM
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There is another alternative. Simply wire a second 40 amp relay in parallel with the first. They share the load and last much longer. Also a big capacitor helps smooth out the voltage fluctuation.

RS
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Old 06-13-2021, 06:44 PM
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There is another alternative. Simply wire a second 40 amp relay in parallel with the first. They share the load and last much longer. Also a big capacitor helps smooth out the voltage fluctuation.

RS
Not only will they share load, they will shift load as well. As one relay heats up, and resistance increases, current will automatically flow down the alternate path. For a fun bar room bet, have two parallel paths serving the same 30 amp load. If all things are equal, fifteen amps will flow down both paths. But if you put a five amp fuse on one leg, the fuse will not blow because the increased resistance of the heated up fuse will send the current down the other leg. The same holds true for a one amp fuse. All magically done with no user intervention.
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Old 06-14-2021, 01:12 PM
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Originally Posted by patrickt View Post
Not only will they share load, they will shift load as well. As one relay heats up, and resistance increases, current will automatically flow down the alternate path. For a fun bar room bet, have two parallel paths serving the same 30 amp load. If all things are equal, fifteen amps will flow down both paths. But if you put a five amp fuse on one leg, the fuse will not blow because the increased resistance of the heated up fuse will send the current down the other leg. The same holds true for a one amp fuse. All magically done with no user intervention.
I wasn't aware of that, but I'm sure my dual relay setup is operating as you indicate. When the original relay failed a few years I doubled up, installing them in parallel, and I've had zero issues since.
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Old 06-14-2021, 01:16 PM
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Quote:
Originally Posted by bkozlow View Post
Generally, it is three words written on the relay "MADE IN CHINA" and if it is Bosch then your amp rating is to low. I would go to a German car dealer in your area and have the parts department find you a HD unit for one of their top model cars, more than likely they will be Bosch no matter what type car. Or you can contact Texas Industrial Supply at texasindustrialelectric.com/relays and look over their inventory. Look at 0332-002-168, if it were to fail then you have other problems in your system.

Bill K
Another option is pulling OEM relays from vehicles in a wrecking yard, er, auto recycling. This would be especially so if they have some German imports you can cannibalize for the necessary items.

I pulled 3 or 4 from a local U-pick and they didn't even charge me for them. With hundreds of cars in the yard and multiple relays per vehicle they don't even bother - especially when most people just pilfer them and don't ask. I guess they focus on things too big to pocket.
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Old 06-14-2021, 03:52 PM
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Originally Posted by cycleguy55 View Post
I wasn't aware of that, but I'm sure my dual relay setup is operating as you indicate. When the original relay failed a few years I doubled up, installing them in parallel, and I've had zero issues since.
OK, it's not the classic method of designing a fail-over circuit, but wtf. Anything that is reliable for a few years on these cars deserves a chance to stay.
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Old 06-14-2021, 05:02 PM
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Fans draw a lot of power i would guess 2 small of a relay
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Old 07-05-2021, 06:17 PM
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My cars original builder used four fans to cover the radiator two thermostatic sensors and adjustable switches dividing the upper pair and lower pair of fans and their controllers. I have incorporated Two Bausch relays. I also supply the current through circuit breakers I did have a problem with My attachment to the circuit breakers and the holder bracket. I used one nut per threaded post clamping the wire terminal end to the plastic breaker holder. That did not last the terminal got hot and melted the plastic enough to break the electric connection. When found that I repaired the melted plastic areas and used two nuts per threaded post off the breakers to the first nut holds the circuit breakers in place in the holder and the wire terminal end is actually clamp the wire terminal ends tightly between the two nuts . It works much better now. The 20 amp breakers supply the current to operate the relays and the 30 amp breaker supply the heavy switched current. sensors control the fans when ever the master switch is on and the switch on the dash can turn on the fans to test and to get a head start on foreseen circumstances.
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Old 07-05-2021, 09:47 PM
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I would see how much the fan is drawing.
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Old 07-10-2021, 03:24 AM
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Default Cooling Fan Failure

You may need to place a snubber across your relay contacts.

A fan is an inductive load. When you switch off the fan relay, the electromagnetic field in the fan collapses, and as a result a very high voltage is generated across the relay contacts. This causes an arc, and eventually the relay contacts deteriorate due to this constant arcing at fan switch off.

A snubber ( series resistor + capacitor) should be placed across the relay contacts to prevent this arcing. Search online for a suitable snubber circuit for a 12v fan.
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