Electric fans suck!

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L31MaxExpress

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Every 8.1 has a 5 blade steel fan, unless it was installed in a Kodiak. Internet lore is they are good for 11,000 peak CFM on that engine/that FEAD pulley ratio.

The trailblazers use a plastic fan with an outer ring that is the same diameter and pulls even more air than the stock 8.1 fan, but it is probably overkill for most cases. Not a lot of other 21.5" fans out there. GMT400 stuff, at least with small blocks, are 19.5" fans. The bolt pattern is different on the Trailblazer fan and most of them have electric fan clutches, but for 2008-2009 they had a standard mechanical fan clutch with the same thread pattern as all the other GM stuff of the era.

As far as I can tell, the Kodiaks actually use the trailblazer fan setup, or something visually very close to it. Depending on what you look at on Rockauto, some of the part numbers interchange.

For some reason, every aftermarket fan clutch I've had seems to engage earlier and cycle more than the OEM GM stuff, which is a bit of a bummer for fuel economy.

The Duramax fan is a bolt in for the 8.1L fan and moves noticeably more air especially around idle.

As for the clutch engaging eariler, it is great for ac and cooling in hotter climates. Idle and around town a/c output will suffer greatly without good airflow across the condenser and the excess head pressure will greatly shorten the life of the compressor. I am considering a couple of 14" pushers in front of my condenser on the van controlled by the PCM.

I suffer more fuel economy loss from the higher ac head pressure and higher engine operating temps making the PCM pull timing than I do from the fan pulling more air. I have seen my intake air hit 170-180°F on a hot day.
 

AuroraGirl

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A few corrections are needed for 1997+ model years. The 5 blade fan was never installed on any big block. The 6.5 diesel received a 9 blade fan, but it was different from the big block fan. The diameter is the same, but the blades look shorter than on the big block. All 454 and at least some of the 8.1 engines came with a 9 blade steel fan. I don't know if it will bolt up/fit on the small block, but the big block fan will suck children and small adults into the grill when the clutch engages. It does sound like a Cessna on take off but if you have an overheating problem with that fan the fan blade isn't the problem. I have no knowledge of a 7 blade fan.
Does the 4.3 use the same mounting pattern for the fan as the SBC(350s etc) just a different clutch and maybe a different sized/pitched/bladed fan?
I hear a chevy 4.3 has a 7 or possibly 11 blade plastic fan with a moderate pitch, and a 90s f150 with a 4.9 i6 uses a 7 blade metal fan with decent pitch to it, can be pretty loud depending on clutch.

I have the ford 4.9 with a 7 blade
You must be registered for see images attach

here someone mounted the aforementioned 4.3 fan on a ford(also it appears to be backward...?)
but I mentioned this all because it sounds like somoene needs a 7 blade metal fan??
You must be registered for see images attach
 

L31MaxExpress

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Does the 4.3 use the same mounting pattern for the fan as the SBC(350s etc) just a different clutch and maybe a different sized/pitched/bladed fan?
I hear a chevy 4.3 has a 7 or possibly 11 blade plastic fan with a moderate pitch, and a 90s f150 with a 4.9 i6 uses a 7 blade metal fan with decent pitch to it, can be pretty loud depending on clutch.

I have the ford 4.9 with a 7 blade
You must be registered for see images attach

here someone mounted the aforementioned 4.3 fan on a ford(also it appears to be backward...?)
but I mentioned this all because it sounds like somoene needs a 7 blade metal fan??
You must be registered for see images attach
4.3 typically has the same water pump, same clutch and same fan in the same chassis.
 

1998_K1500_Sub

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...a large ac condenser pumping heat out of dual evaporators in front of the radiator. The mechanical fan would be at 2,000+ rpm at that point and probably pulling 8-10,000 cfm. At 3,000 rpm compressor speed, the compressor is cranking out ~25,000 BTU into the condenser.

25,000BTU dumped into 2000cfm would yield a ballpark ~11degF heat rise, i.e., the "preheated" temperature of the air entering the radiator is increased by ~11degF. The temp rise varies inversely with CFM, e.g., at 1000 CFM the rise is ~22degF, at 10,000CFM it's ~2.2degF.

Other factors will cause this to vary but for a ballpark estimate, this should do.


Assumptions:

Ambient conditions - Dry air at or around 68degF, thereby having density of 1.29kg/m^3 and specific heat 1000 J/kg*degK.
 
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L31MaxExpress

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Ambient air conditions in the shade were 104°F, 45% humidity and ~29.70 baro pressure. The ambient temp showing on my GM compass/temp mirror measured above the road surface, in heavy traffic congestion behind my grille in good airflow was 115°F. Even though the fans free flow 6,000 cfm, in the cooling stack its probably 2,500-3,000 cfm max.

With the mechanical fan and shroud it has not broken 185°F.

Also keep in mind it has a trans cooler that is 1' square in front of the condenser, then the condenser, then the radiator. The trans fluid leaving the radiator is in the 130-140°F range with the trans operating at 160°F.
 
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1998_K1500_Sub

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Ambient air conditions in the shade were 104°F, 45% humidity and ~29.70 baro pressure. The ambient temp showing on my GM compass/temp mirror measured above the road surface, in heavy traffic congestion behind my grille in good airflow was 115°F. Even though the fans free flow 6,000 cfm, in the cooling stack its probably 2,500-3,000 cfm max.

With the mechanical fan and shroud it has not broken 185°F.

Any idea what the heat rejection into the coolant might be for that 383 under similar operating conditions (load, etc.)?
 
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