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Has anyone changed fan blade type on your engines to get better cooling? any impacts on water pump life?

I have 3 fans to chose from...the first is a 4 blade fan with smallish blades (std one from LMC - car application?), the second is a 5 blade fan with irregular fan blade spacing, and the 3rd is the same a 2 but slightly wider blades and have a "lip" or turnup at the end.. all were removed from misc chevy/gmc trucks over the years...

would you know which is correct for a 1960 261? would changing to a 5 blade fan provide better cooling at low speeds?

I would use the 3rd one with wider blades as I think it would pull more air but, I have no scientific data to back it up. I have not had the type of fan change water pump life. If the fan is out of balance, and it is on a long extension, then that could have an impact on water pump bearing wear. I am not sure which would be original.

I swapped mine for a 5 blade from a '58 School Bus along with the matching factory shroud, and did see an improvement in cooling at idle speeds. Operating temps dropped about 10-15 degrees average. This was a change from the factory 4 blade and an aftermarket shroud. No other changes were made.

There is a reason you are seeking better cooling. If it's an AD that 261 is in, do you have the water pump adapter plate? Once the fan is centered on the radiator, the 216 fan is the go-to version.

I find for the most part they did a great job engineering the cooling system and if you diagnose properly, you can get it working perfectly without shrouds, larger fans, etc. Also, you need to PM Maybelline (Matt) and ask him about his bypass thermostat system that he has engineered for that engine.

The 261 is in a 1950 1 ton truck. I have the water pump relocation kit installed. I have a 180F thermostat installed. Cools fine while driving and no over heating problems... The temp rises a bit in traffic or around town on hot days.. Already had the 3 fans and thought a 5 blade fan would help in those conditions.

Did trucks get different fans than car applications?

The irregular blade spacing reduces fan noise.

interesting, that makes sense!

would the water pump pulley size also be different with the 5 and 6 blade fan blades (as compared to 4 blade fans)... or asked another way... were 5 and 6 blade fans run at lower rpm than the 4 blade fans?

The five and six blade fans work off the same pulleys as the four blade fans.

GM offered a six blade dealer option for extra cooling in either city traffic with lots of stop and go or field work in which the truck would have to idle for long periods.

The five blade fans with irregular spacing came with big trucks with the 261 or 3/4 and 1 tons with the heavy duty cooling option (at least for the TF series). The five blade fan fits inside a shroud that fits into brackets on a radiator with a wider, higher capacity core. The irregular spacing looks goofy, but it has something to do with creating better flow by breaking up the wind flow.

When I converted to A/C, the four blade fan on my '57 235 needed help. I installed a 19" GM optional six blade fan. It helped quite a bit. Then I came across a '57 6400 that had come with a 261 that still had the irregular 20" five blade fan and the shroud. The radiator was shot, but I salvaged the brackets and mounted the shroud on my radiator and installed the five blade fan.

I don't notice any difference between the six blade/no shroud and the five blade/shroud performance.

If you can find a shroud, I'd use the five blade because they were designed to work in tandem on the 261. Without a shroud, I'd use a six blade because it was not designed to require a shroud.

You won't go wrong either way, IMHO.

Matt

thanks a lot... that answers most of my questions

I have a real good 4 core radiator I found out of a 1 ton that Im going to replace the new 3 core radiator I purchased from LMC.

at that time I will also change fans to the 5 or 6 blade fans... will see if I can find the shroud you mentioned

hope to have a system that can run a 180F thermostat and maintain temp in traffic or stop and go in 100F+ weather

again thanks for help... lots of knowledge here

One thing most folks don't know about a shroud is the position where it needs to mount. The fan blade should have half its blades covered by the shroud. That usually means the back of the shroud should be approximately in line with the fan hub, so half the blade protrudes out the back. If the fan is totally enclosed, the shroud will actually restrict the airflow.
Jerry

You might want to consider a 160 degree thermostat if you are going to be in 100 degree plus weather. I switched over from a 180 when I moved to Arizona and am much happier with it. I run it year round because I don't have much need for heat.


Matt