I got the Napa belt a while ago. It worked fine.

Fan clutch causes premature belt failure?
 

My FB was in storage for 14 years and is now back on the road, running OK as far as I can tell. I replaced the belt because it looked old and cracked. Then it was loose. So I tightened it up. Loose again. No more alternator travel, so a new one. Now it has stretched out too, to the point that I've run out of alternator travel again. Two belts in about 1000km or less. I'm wondering if it isn't the fault of the belt! Everything seems to turn easily. It drives the alternator and water pump - nothing else left down there.

At one point on the highway it sounded like the fan was going and stopping - like a gusting cross wind sound. It was near the end of that belt's life so I assumed it was slipping, then gripping. But perhaps the clutch is to blame? Are there any symptoms I should be checking for, or is my belt wear indicative of this problem? Anything else that could be an issue?

Thermostat. The clutch will operate under a specific temp. If it is too hot it will begin to lock up and cool the radiator. When it is cold, it will not lock up and freewheel.


I have the stock MAZDA belt, and a YOOHOO belt from Pineapple. 3 years and still running strong.

I used a belt from napa when I first got it running, and it promptly snapped within 1k miles. Went to Mazda and never looked back.

PS When the NAPA belt blew the YooHoo belt was there to take me the 3 miles home.

Thanks for the response...!

So am I correct in understanding that the clutch can lock up and cause the fan to spin faster than intended? My understanding of a fan clutch like this is that it doesn't really lock up, but is viscously coupled between the drive pulley and the blades. So revving the engine up only spins the fan faster to a point, after which the air resistance against the blades exceeds the internal viscous resistance of the clutch and thus prevents the fan from becoming a propellor... :rolleyes:

I have a tough time with the idea of a thermostat in there... it would have to be purely mechanical with only the heat in the clutch to determine its operating mode. And that might not be indicative of the coolant temperature. Can you clarify how this works? I don't really want to swap out the clutch if that isn't my problem! My suspicion is that the belt I've installed just doesn't have enough 'stick' to prevent slippage even when tight. The shallow angle across the water pump doesn't help things either. Maybe the water pump bearing is getting stiff and the belt wear is actually there...

I don't get any squeaking or burning belt smells though.

There is a theromstat in the clutch. The fins on the front of the fan are for exactly that, absorbing radient heat through the fan to the the thermostat:

http://auto.howstuffworks.com/cooling-system.htm

"Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This special viscous clutch is much like the viscous coupling sometimes found in all-wheel drive cars."

Don't get the fan thermostat confused with the cooling systems thermostat.

The thermostat in the cooling system is essentially a temperature controlled valve which controls the flow of the coolant to the radiator. Coolant is stopped from flowing from the engine to the radiator until the motor is up to temperature.

The thermostat in the fan clutch controls the cooling fan. It is located in the finned hub of the cooling fan. If the hub detects that it is hot, the clutch engages and the fan spins. If it is cool, the fan clutch is disengaged and the fan spins freely, without a load on the motor.

So there are a few ways the clutch can operate. The most simple method would require a fluid that becomes more viscous with temperature. Alternatively, a bimetallic strip can be used to adjust how much fluid is allowed into the coupling zone, thus controlling how much (or how little) slip is allowed.

If the bimetallic strip stayed in the full on position, the fan would turn faster that it would otherwise. You wouldn't be able to tell by spinning the fan by hand with the engine turned off - it would spin whether there was a problem or not. I'm going to assume that this is the method used by Mazda, as the simple fluid viscosity trick would work forever, until the thing sprang a leak anyway. Do we know for sure that there is a thermostatically controlled actuator in these?

If the fan is always turning faster than it should because the clutch is fully engaged, then it stands to reason that the belt would want to slip. The angle across the water pump taken by the belt is extremely shallow - I can see it slipping there quite easily. A bit of a design flaw really.

So my choice is likely to replace the clutch or go to an electric fan system such as that offered by Black Dragon. I think the electric idea might be a better one - it would certainly take some of the strain off of the water pump bearings. Anyone had problems with the electric fan system?

Hi ray green!

I need your help, if possible.

I bought an engine in the US (I live in Brazil) and it has a stock water pump pulley (double belt, fan pulley) like the one you showed in the pictures.

I need some room in order to adapt the engine in another car and I want to know if is possible to swap the pulley without disassemble the water pump housing. I'm going to use electrical fan.

Thank you in advance.

Marcos.

Hey Marcos,

Yes, but the shaft on the water pump extends out to the front face of the dual pulley, so beyond removing the fan and its aluminum mounting shaft you won't gain much space.

Just remove the clutch fan, underneath with be 4 bolts holding the aluminum mounting shaft to the water pump and pulley.

Here's a couple photos for reference:

Love that engine bay, I should spend time cleaning up mine soon.

OK I'm kinda haven the same problem I'm new to this site and new to the rx7 world. I brought a 90 rx7 very off my close boi car ran good until the belt snapped l, looked old to I replaced it with one from autozone drove it for a Lititle a snapped that one to.so it the stock pulley's the alt starts to squeal and then brakes the belt I went throw 4 belts, I order a alt with a dual pulley on it. It starts to squeal also then snapped both belts. But the funny part is the volts seem to be fine but it get funny when it comes to this, the only way the alts squeal if the battery terminal's are connected but once I take the negative or both off the squealing stops and I can run the car fine but the battery is not connected I been stuck for two weeks please HELP!!!