I didn't like the design of the 8 blade fan on my 06 H3 so I changed it. I removed every other blade and smoothed out the pedestals where the 4 blades were. I noticed no difference in engine temperature as read from an OBDII scanner driving in town and on the highway.

The outside temperature was 92F and the highest ECT was 192F with the AC running using the 4 blade fan.

I saw an increase in my instantaneous highway MPG of over 1 MPG and about a 1 MPG increase in town. Here is some load and fuel consumption data with the stock 8 blade fan and my 4 blade fan.

8 blade fan:
Idle in park In drive with parking brake on

Engine load 27.1% 32.2%

Gal/hr 0.39 0.47


4 blade fan:
Idle in park In drive with parking brake on

Engine load 26.1% 30.2%

Gal/hr 0.34 0.40

This data shows that the engine load actually decreased and used less fuel with the 4 blade fan. The 4 blade fan actually turns faster than the 8 blade fan. This may seem confusing, but here is what happens. The fan is connected to the water pump pulley by a viscous coupling (notice how you can spin the fan when the engine is off?) that can only transmit a limited amount of torque when it is not engaged by the thermo clutch. The water pump turns at a fixed speed controlled by the engine idle. The 4 blade fan takes less torque to spin for a given speed versus the 8 blade fan. The lower load requirement of the 4 blade fan causes it to spin faster increasing its efficiency.

This mod isn't for everyone. Also the new fan blade design from GM has seven blades so someone at GM must not have liked the 8 blade design either.

 

It'd be interesting to see the same data parameters in your 4 blade fan versus Doc's electric fan.

 

Very interesting, although it would have never dawned on me that someone could dislike a 8 blade fan design so much.

 

I'd like to see some pics of this mod and how did you do it.

 

I too am impressed
Show us some pictures
and where did you get the four blade fan ?

 

Sorry, my table didn't print out that clear. Let me run the 4 blade fan for a few more weeks to see how things work out before anyone spends any money.

@ Broken Halo - His load and gal/hr would be better when the fan isn't running. I'm guessing his values would also be better when the fan is running.

@ MuDnYrI - I did come off pretty bad/stupid toward the 8 blade fan.

@ drtom - The new 7 blade fan is about $45 with shipping.

ACDELCO 15-80698 Engine Cooling Fan | eBay

The 10-20% reduction in fuel consumption was just for idle where the engine is just driving the fan and accessories. There is less of a reduction in fuel consumption when the engine is moving the vehicle. I just didn't want anyone to assume that this would save 10-20% in total fuel consumption.

I removed the 8 blade fan/clutch assembly and cut off every other blade about 1/4" above the base using a dremel with a cutoff wheel. Then I used a milling bit in the dremel to remove the remaining pedestals to be flush with the base.

 

My fan has eleven blades, I guess the v8 needs more cooling.

 

Eleven ... what does that remind me of .... Oh yeah ... Spinal Tap!

Spinal Tap - 11 - YouTube

 

I should have mentioned that I had the 3.5L with the stock 180 F thermostat.

 

Just an update. Not problems yet. I noticed that it takes longer to reach normal temperature now. For example, 75 F out, four passengers in the H3, it took several miles with city driving to reach an ECT of 175F. I haven't been traveling my normal route so I can't provide new MPG data.

Last night I traveled about 25 highway miles and the ECT never got above 174 F with an outside temperature of about 68F.

What's the problem? The auto tranny torque converter lockup is dependent on temperature. The threshold seems to be around an ECT of 175F - I can't measure actual tranny fluid temperature. The longer it takes to heat up, the torque converter lockup is delayed, and lowers the MPG.

I may try to block off a couple holes in the grille.