Fan clutch or electric

[Varinn]

My fan clutch is stuck on and I'm debating just going electric while I'm in the midst of fixing this. I live in a moderate climate with peak temps around 25-30 celsius. I use the AC in the car during the summer months and currently have a stock 80 degree thermostat.

Is the auxillary fan enough to keep the engine cool on its own in traffic? What temperature switch should I run? I was thinking 82 or 88 degrees. I am not opposed to grabbing a puller fan to run as well if needed.

[Cabriolet]

you will 100% need a puller fan

[Varinn]

K, I was expecting as much. The SPAL units seem popular is there a go-to direct fit model? I can handle the wiring myself.

[oldmann]

Keep the clutch, My clutch wouldn't grab when got hot, car would overheat in traffic. Replaced clutch, issue is gone, I had a switch wired into the high side of aux fan and it would keep the car cool in 100 deg. weather here in Denver, Colo., But with the clutch working, I have no more overheat issue's either. Aux fan on high was noisy, as would most other electrics.

And the clutch was $12 at a salvage yard.

[Varinn]

My only issue with the clutch fan is the noise at low speed crawling and I hear the electric fans makes it a touch more responsive which would go well with my lightweight flywheel

[Cabriolet]

Varinn, as long as you arent running a big sound system electric is way better.

[jlevie]

In terms of simplicity and reliability the OE configuration is better on a street car. To equal the performance of the stock fan you need a 16" electric fan rated for at least 2000cfm. When running that will make a lot more noise than the stock fan because the blade area is much less. If the car has AC the stock aux fan must be maintained and electric fan mounted between the engine and radiator, which leads to the next problem. Don't even consider using any sort of through the radiator mounts. They can and will eat holes in the radiator fin tubes. So you must fabricate a fan mount. If you don't include a shroud in that mount the fan needs to be within 1/8" of the radiator (1/6" is much better). The fan needs to turn on when the radiator temperature is only a couple of degrees above the stock thermostat rating. A 82-83C thermo switch is what you want. When AC is retained that means you can't use either the low or high speed aux relays and will have to add a relay.

The stock fan clutch should be replaced at the service life of the rest of the cooling system (10yr/100k). If that schedule is followed, and it should be, you will probably never have a problem with fan clutch.

Now a race car is a different deal. The stock fan is a parasitic power loss and the only times the fan is necessary on a race car are in the paddock or during a red flag event. So replacing the stock fan with an electric makes sense.

[Varinn]

I'm always glad when Levie posts up with his input. My car is primarily a street car and I guess for the extra performance boost I can just remove the mechanical fan whenever I hop out onto the track. I will consider my options for a couple of days and decide what I want to do soon.

[jlevie]

If the fan clutch is good, don't remove it for a track weekend, the slight power loss won't really make a difference and you will really wish you had it if a red flag condition occurs.

In a race car it just might make a difference in position. We are only talking about maybe 1hp.

[Varinn]

Jim, is it normal condition for the fan clutch to be the loudest part of the car under 60kph or so? My fan is significantly louder than my stock eberspacher exhaust at all rpm's in the bottom gears regardless of engine temperature. My car sounds like a semi when accelerating from a light. Also, I'm going to send you a PM later tonight regarding some questions about my first 3 day track weekend/drivers training, hopefully you can offer me some pointers on a few questions I have so I can go in prepared and focus on the lessons, not the car.

[jlevie]

In case you don't know, the fan clutch is thermostatically operated. It responds to the temperature of the air coming off the radiator, engaging when that air is hot enough. Except in very high temperature ambients the air flow through the radiator when the car is moving at 45kph or more is sufficient to keep the radiator cool enough that the clutch will disengage. And since the clutch is viscous it will slip at higher engine speeds, even when engaged.

So the fan should be pretty much silent if it is working properly and there aren't problems with the cooling system. If the car has been idling or has been driven slowly in stop and go traffic for a while the engine and radiator temperature will be high enough to engage the fan and you may hear it accelerating away from a stop. But once the car is moving for a bit at ~45kph or more the fan should disengage.

In this case I'd suspect that you have, at the least, a bad fan clutch. Given where you are, I'd also suspect that the car has a somewhat clogged up radiator. Which would not be surprising in a 20'ish year old car. I, and most pro's, figure the life of the cooling system at 10yr/100k. At which point the entire cooling system should be replaced (radiator, expansion tank, cap, thermostat, water pump, hoses, and fan clutch). The plastic & rubber bits get hard and brittle, the radiator may be partially plugged if the car hasn't been religiously maintained, and the clutch and water pump will be worn. Those parts can, and frequently do last longer, but a bit of extra stress can result is a catastrophic failure. The potential cost of such a failure is a good bit greater than the cost of the cooling system parts. If you are going to track the car (putting it under high stress) the cooling system is one of the things I'd address before going on track. The other things are a good set of brake pads (like HPS or better), street tires with at least 3/32 of tread left, and a suspension that is in good condition wear wise.

When you get to the track check your ego at the gate. You may think that you are a good driver, but you don't yet know how much you don't know. With the right attitude you will progress faster. And don't hesitate to admit that you didn't do something right or that you made a mistake. Good judgement comes from having made bad decisions and survived them (and are able to admit to the mistake and learn from it). In general HPDE instructors are very good and when you drive out on track you are entering their world. They know how to go fast and can teach you, if you will listen.

[Varinn]

My temperature never climbs beyond this point, even with A/C on, mid summer, in traffic or idling after an autocross run. The fan does make noise even immediatly after startup and it stays loud at all times. I've heard they often are loud for the first couple minutes, and when the coolant is fully up to temp at low speeds. Mine is always loud. I will buy a new fan clutch today but which brand should I get? Do you have a preference? My entire cooling system is under 15,000km, the only parts that were not purchased new were the radiator and fan clutch. The radiator was cleaned before install however and the fins looked to be in ok condition, I can try removing it to inspect/replace in a few weeks

Note: the gauge moves freely and starts appropriately from cold, working gradually higher at a relatively normal pace.

[jlevie]

By clogged I mean internal obstructions in the radiator fin tubes. Not what you can see visually.

If the fan makes noise on a cold start, the clutch is bad. Use an OE clutch like you get from a BMW dealer.