fan clutch job observations

markxengineering

Active member
The fan that came out (installed by previous owner) looks like it was the wrong one for at T1N, from a later model Sprinter. Price difference at SD Europarts is minimal between the two, but there are many design changes. Especially relevant are 1) Which flows more? and 2) Which turns on at a lower temperature? 3) Could the later model fan be considered an "upgrade" for T1N's?

Side by side:

I have forwarded this info to a friend who does nothing but design + test fans for his feedback, so will hold off on blade feature commentary until then.
The ring around the newer design fan makes it more of a PITA to undo the central fastening screw, but the increased spacing in between blades helps a little bit with access. Call it a wash. It took me a couple hours to do this job, which is reportedly possible in 15 minutes for someone with smaller hands and the right tools. I should have just moved the radiator.


Noticeable in the above photo is that the fan is not separate from the thermal clutch in the newer design, must replace both as an assembly. Fewer and fatter cooling fins on newer design = less efficient heat transfer, but cheaper to make. There is a through passage for airflow near the OD of the newer clutch which is blocked in the older one. This would cause more heat transfer. Maybe another wash?


From the other side, cooling fin design a lot cheaper and less efficient again for the newer part. Both have balancing pads in the clutch. I forgot to compare bearing sizes and try to see if fan was balanced separately from the clutch in each case. The blades do get bent a bit during handling and installation, but hopefully nothing that won't spring back. I wonder how much these parts creep with age and heat, my guess would be a lot, making fan balancing semi-pointless anyway.

Both fans themselves are made from 30% glass filled nylon, as are many plastic engine parts.


Comments welcome..
 

Heatnairguy

New member
The newer fan blade appears to have more pitch which should provide better airflow when idling with the AC on. It also has the newer kind of blade design that has the leading edge of the outsides of the blades leading the rest of the blade. That is done to prevent the normal tendency of the airflow to push outward from the root and spill off the ends of the blades, losing efficiency. The ring on the outside ends of the blades also contributes to that prevention of efficiency robbing spillage while at the same time increasing structural rigidity. The latter as well as the fewer number of more robust blades should have the potential to increase durability. All told, if the fitment is the same, and barring any other unknown negatives, I’d choose the newer version.


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markxengineering

Active member
Increasing diameter will increase flow and pressure, however a tip-ring will reduce tip-effect. My guess is that the fan was made smaller and had a tip-ring added to reduce power consumption at the duty point.

Increasing Total all blade tip chord will increase flow with some pressure increase. Measure the tip chord of one blade on each fan and multiply by the number of blades. It’s probably closer in total then it looks. If it’s within +/-10% then it’s was probably nominally the same, but with the shift to a 3D blade design with tip-ring a slightly different total chord was needed.

Overall, the tip-ring fan will take less power = slightly better fuel economy. Asymmetric blades are to diminish intensity of tonal noise - both look to have been optimized well for tonal noise.
Unfortunately I can’t make the measurements suggested because the install is done
 

Heatnairguy

New member
There is also the fact that without the air that usually spills back forward off of the tips toward the radiator due to the pressure differential, the whole chord is throwing air back towards the engine and the gap around the outside of the ring to the inside of the shroud could act like a Venturi then and move even more air through the radiator, giving an even better net CFM at any given speed.


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