tech

Has any body used a smaller fan pulley on 92-2001 xj , I know the 84-91 xj has a smaller pulley . just to speed up the fan speed a little to help with the xj temp problems ? I've done this on some chevys I had .

tech

Wow I can't be leave no one have done this . it looks like you can use a smaller pulley on the water pump to . It would be nice if some one made a larger crank pulley , that would speed up everything .

Bugout4x4

Know what? This is a great concept! I live in the Az desert and WILL be trying this on the fan next spring on my 97! I wonder if there will be any belt issues? Would it need a shorter belt I wonder? Or would the adjuster have plenty to make up the difference?

I have done this in racing, but in reverse with bigger pulleys to reduce that little bit of power loss when driving the accessories.

I'm not sure if the water pump turning faster would be an advantage though? At some point you can actually have it going through the radiator too fast for it to have time to cool properly.

neverenuff

I spent a few Saturdays looking around at pick and save looking for a smaller pulley to fit the water pump pattern for 99 4.0 liter. I did find a close fit from a GM mini van. after doing the math it was 10% smaller than the stock one. I figure that means the GM pulley was turning approx. 10% faster(?) .... anyway I would not recommend underdriving the pulley to speed up the impeller in the water pump. I used this smaller pulley for two years and each year I had to replace the water pump do to leakage caused by water erosion through the side of the pump housing.May sound crazy but the erosion was quite bad in the areas around the impeller. Took off the GM pulley and installed the stock one and added a hi flow water pump. So far so good.

Bugout4x4

Probably just like the erosion that happens to a watercraft propeller from turning so fast it causes "cavitation".

Thanks for sharing that tidbit, nice to find out from someone who has tried it on the pump already.

tech

I was thinking of just speeding up the fan to pull more air not really thinking of speeding up the water pump .

Bugout4x4

This is what I read... But I am right behind you with the fan speed! I need it out here... and was actually thinking about an eliminator for summer off road trips.

cruiser54

Just use the Napa 272310 fan clutch from a Grand with the 4.0.

It spins at 60% of engine speed versus 40% with stock.

Willys55

Dam it Pete, you beat me too it.....not only that, but a smaller pulley will spin the fan slower boys...it's all about physics

cruiser54

Figure most fan clutches are toast by now, just get the GC one.

Order by part number to get the correct one. 272310 Napa.

Bugout4x4

You almost had me with this... Smaller making it go slower per revolution would indeed be the case if the fan pulley was driving the crank pulley, rather than the crank pulley driving the fan pulley.

Easy comparison in physics to this situation would be the circumference length difference between a car tire and an 11-24.5 truck tire. The smaller car tire is going to make about twice the revolutions per mile as the larger truck tire.

But I went and looked and you and Cruiser are right, it's not practical, You can't go much smaller without hitting the pump housing so it might not be much of a gain at all.

Bugout4x4

Good call Cruiser...I went and looked and you can't go much smaller without hitting the housing anyhow. Not enough to make much of a difference anyways.