Measuring viscous fan RPM and analysis

[calbiker]

Here's a plot of just viscous fan rpm and air temperature passing through the radiator on the return trip.

View attachment 196001

The red plot is fan rpm with y-axis on the right. When starting engine the fan starts a 1000 rpm but quickly drops to below 500. It appears when air temperature gets to 170 F the fan begins to activate. The fan might be full on when air temperature rises above 180 F. At the 80 minute mark the vehicles is on the Nojoqui Grade where fan is at 3000 rpm. This viscous fan is original, so 15 years old. A new fan might spool up to higher rpm.

The rpm plot has instances where data goes to zero. These are "time-out" measurement errors. If the fan reflected signal is not detected within a reasonable amount of time then "zero" is logged.

I can provide details and code if anybody is interested in building an Arduino based fan rpm and fan air temperature data logger. Costs might be ~$40.

 

[owner]

A hall effect sensor might be more reliable long term than diodes. A screw could be screwed into one of the fan blades to trigger it.

 

[220629]

A hall effect sensor might be more reliable long term than diodes. A screw could be screwed into one of the fan blades to trigger it.

Could be a good alternative depending upon the controller that is used.

Balance would be a concern for me. I wonder whether a thin steel washer with an aluminum pop rivet might have less mass than a screw/bolt, but still provide enough field for the Hall effect sensor.

vic

 

[marklg]

Could be a good alternative depending upon the controller that is used.

Balance would be a concern for me. I wonder whether a thin steel washer with an aluminum pop rivet might have less mass than a screw/bolt, but still provide enough field for the Hall effect sensor.

vic

I think anything substantial is going to unbalance the fan blade. How about a bit of conductive tape?

Regards,

Mark

 

[tbuyan]

I think anything substantial is going to unbalance the fan blade.

Put a trigger on each blade and divide the resultant rpm by the number of blades. 7?

 

[calbiker]

I would be very hesitant placing any weight at the tip of the fan blade. How fast is the tip of the blade moving when fan is rotating at 3400 rpm with a 17 inch diameter blade?

v = 17" * 3.14 * 3400 rpm * 60 hr/min / (12 "/ft * 5280 ft/mi)
v = 172 mph

That's damn fast! No wonder the fan roars.

I'm using aluminum tin foil taped to the tip of one fan blade. That seems to be working well.

I was going to try a laser diode, but they never arrived from China via Aliexpress.

 

[calbiker]

Got new data from my Baja trip.

In summary:
1. When fan is locked it spins ~1.5 times faster than engine rpm. In Post 6, based on pully dimensions, I calculated fan speed should be 1.5 X greater (which is now verified).
2. If coolant temp is less than 200 F (which corresponds to fan air temperature of 175 F) the fan will spin at ~500 rpm.
3. If coolant temp reaches 204 F (which corresponds to fan air temp of 185 F) the fan will be locked and spin at 1.5 times engine rpm.
4. Fan speed ramps up between coolant temp 200 to 204 F.
5. When fan is locked, fan air temperature gets to within 5 degrees of coolant temperature. This shows the radiator and fan specifications are well designed.

This viscous fan is still original, on a '06 3500 T1N @ 120,000 miles.

 

[calbiker]

More fan data...



3 plots seen are coolant temp, viscous fan temp (with scale to the left) and viscous fan rpm (red plot with scale on the right y-axis). Ambient temp is about 70 F throughout the 3+ hour drive.

Some observations:

1. When locked, the fan operates at ~1.5 times engine rpm. I haven't seen fan rpm greater than 3000. Not sure if that's a measurement issue I have with the hardware/software or an actual fan limit.

2. Max coolant temp is 214 F at 86 minute mark while fan temp is at 186 F. The fan isn't fully locked at this moment as it's operating at 1800 rpm while engine is at 2770 rpm. Within a minute later (with 99% load) the fan is locked at 3000 rpm and engine at 2059 rpm. Coolant temp dropped to 204 and fan temp dropped to 172 F.

3. At the 127 minute mark the vehicle is on a long down hill, coasting to max 71 mph. For most of that down hill the viscous fan is operating between 1500 to 1700 rpm. From top to bottom of hill coolant temp drops from 207 to 179 F (delta 28 F), while fan temp drops from 180 to 97 F (delta 83 F). It appears to me the thermostat closes during the downhill, preventing the coolant temp to drop further. With thermostat closed, temperature through the radiator stack can drop faster.

4. At the very end of the trip the vehicle is stationary while idling in neutral for a few minutes. Coolant is 192 F and fan temp is 164 F. The fan locks up at 940 rpm while engine is at 650 rpm. Even with fan locked, fan temp rises to 168 F while coolant drops to 187 F.

 

[autostaretx]

Nice data ... a question i have is "what's the fan's pitch"?
Or, stated another way: what would its RPM be at in a (say) 60 mph breeze?
I'm wondering if your downhill example is really just the fan spinning in the wind.

--dick

 

[calbiker]

Nice data ... a question i have is "what's the fan's pitch"?
Or, stated another way: what would its RPM be at in a (say) 60 mph breeze?
I'm wondering if your downhill example is really just the fan spinning in the wind.

--dick

"Wind" speed doesn't appear to be a factor. During the start of the trip (when temperatures haven't stabilized yet) while traveling at 10 mph, the fan speed is 480 rpm and engine is at 1712 rpm. Then at 63 mph, fan speed is 500 rpm while engine is at 2400 rpm. Regardless of speed, when temps are cool, the fan likes to hover around 500 rpm.

 

[bigb]

Great thread, thanks for the info. Have you considered the effect of the fan at idle with AC running? Is it possible that a bad fan clutch that will not allow fan to lock at idle could be a reason for dash AC to blow warmer than normal? I remember on our old 300D there was an electric pusher fan on the front of the radiator which was to keep air moving thru the AC condenser, it would activate thermostatically but only when the AC was in use..

 

[glasseye]

Noteworthy is when first starting engine, fan rpm is 1.44 times greater than engine rpm. It takes a few minutes for fan rpm to drop below 500.

That's precisely what I'm observing with my newly installed fan. I can't estimate coolant temp that invokes fan slow-down after startup, but it's fully hooked up on cold start and then quickly disconnects in less than a minute, I'd say. That's in roughly 70F temps and low LOD for the first few minutes.

 

[calbiker]

Great thread, thanks for the info. Have you considered the effect of the fan at idle with AC running? Is it possible that a bad fan clutch that will not allow fan to lock at idle could be a reason for dash AC to blow warmer than normal? I remember on our old 300D there was an electric pusher fan on the front of the radiator which was to keep air moving thru the AC condenser, it would activate thermostatically but only when the AC was in use..

The T1N also has an electric fan in front of the radiator. It turns ON when AC refrigerant pressure exceeds a specific value or if coolant temperature exceeds somewhere around 225 F. I conducted coolant temperature testing when manually engaging the electric fan some 4 years ago. I saw virtually no effect on coolant temperature when the vehicle is in motion. I'm sure the electric fan has value when vehicle is stationary.

If you see warmer than normal dash AC then usually there's not enough refrigerant in the system.

 

[calbiker]

My friends Sprinter motorhome has overheating issues during the past year. I met up with him at Gooseberry Mesa (Utah). There I installed an Arduino fan tach and temperature sensor. He had already installed a Mercedes viscous fan (with no thermal improvements) and then he installed a Duralast fan clutch. Still no improvement. It was time to measure fan rpm. I had built an extra fan rpm datalogger for Vic, but he returned it when he departed the forum . Time to put it to good use!

The two plots FanC. (my rig) and FanT. (friends) are us traveling from Gooseberry Mesa to Hurricane Ut. The first 2/3 of the plot is on a washboard dirt road. The trip is on mostly level or downhill when on the highway. Not a good test for overheating but it is the only time we were able to drive together.





The left side scale is fan temperature in deg.F. Right side scale is fan rpm. Time is in minutes. FanC. rpm data drops out between 30 and 40 minutes. The infrared sensor quits working when it gets too hot. The vehicle was not moving at that point in time, waiting for traffic to open up to enter highway. rpm measurements resume when on the highway

There are major differences in fan rpm. My fan gets up to 1200 rpm at start and then settles around 500 rpm for the entire trip. The engine never heats up enough to warrant further action.

On the other hand, the Duralast fan appears to be locked the entire time. Minimum rpm is ~1000, which is 1.5 times idle. Max rpm is near 4000 when accelerating from the dirt road onto the highway.

I'm expecting further data from him.

EDIT: a few more data points:





My oil temperature doesn't get above 200F until I get to the highway, while the other rig gets to 200F after 20 minutes, traveling at 20 mph.

 

[calbiker]

More data from my friend's rig which exhibits some overheating. He lately installed a Duralast fan clutch.



The orange plot (FanT) is stitched into his Nautabox data. Just prior to the 50 minute mark and after 112 minutes the vehicle is stationary, idling. Fan is at 1000 rpm, which is 1.5 times engine idle speed. Despite fan at 1000 rpm, the fan temperature rises to 187 and 167 F. Not sure what to make of that. Though oil temperature drops significantly during engine idle, H2O remains around 190 F. The vehicle was going at about 61 mph (2500 rpm) during most of the trip. Fan is around 3000 rpm. Though it appears the fan is locked at idle (600 engine rpm vs. fan 1000 rpm), it never locks up when vehicle is moving.



The vehicle peaks on a hill at the 250 min mark: oil = 264, H2O = 221, ATF = 217, FanT = 178 F, engine = 3000 rpm. The fan should be fully locked, but it remains around 3000 rpm (with engine at 3000 rpm) as the graph below shows. Either the fan isn't doing its job or there's a measurement error.




In the past he kept the heater on (while cooking in the cab) just to keep engine temperatures lower.

 

[Midwestdrifter]

Sounds like the duralast clutch doesn't lock up at all, but instead just has a thicker coupling fluid. So the unlocked drag is enough for nearly full RPM at idle, but significantly less at higher engine RPM.

 

[marklg]

Sounds like the duralast clutch doesn't lock up at all, but instead just has a thicker coupling fluid. So the unlocked drag is enough for nearly full RPM at idle, but significantly less at higher engine RPM.

It is very unfortunate that there seems to not be a good choice for a viscous clutch fan. Every brand, including the OEM Mercedes has issues, at least with some samples. Maybe they will start stealing fan clutches instead of Cats, although there is no way for a thief to know a good one from a bad one.

Very few people, maybe now just @calbiker are able to make sufficient measurements to tell if they are working adequately. That is sad.

Regards,

Mark

 

[Midwestdrifter]

Someone probably just needs to find a clutch and fan combo thats pretty close to the same dimensions, and then I can draw up an adapter flange to mount to the T1N water pump. I guess the other option is to just laser cut a solid hub plate, and we can all run fixed on fans!

 

[rollerbearing]

Not sure if this is even possible - drill a drain for the viscous fluid and then pump in JB weld? Wouldn't even need to bond well internally - just jam the mechanism up so it locks.

 

[Midwestdrifter]

Not sure if this is even possible - drill a drain for the viscous fluid and then pump in JB weld? Wouldn't even need to bond well internally - just jam the mechanism up so it locks.

What I have seen on other vehicles, is folks just run a small sheetmeal screw directly into the ball bearing. Not sure its ideal, but does work for many.