POLL: Double W124 fan, or large W126 fan - Page 2 - PeachParts Mercedes-Benz Forum

funola · #16 05-04-2018, 08:54 AM

Quote:

Originally Posted by t walgamuth

You have backup if one goes out but it makes that bit more complexity. Tough choice.

Well made electric fans are very reliable to start with. Wiring 2 fans in parallel can hardly be called more complexity. 2 fans covers more surface area than a single large fan and provide better cooling. Together with the redundancy, it's an easy choice. 2 fans win hands down.

Squiggle Dog · #17 05-04-2018, 01:27 PM

I don't think I've yet seen (or at least, noticed) a car where the auxiliary fan doesn't operate when the hood is open. That's a new one to me. I'm pretty sure my roommate's 1991 W126 350SDL's auxiliary fans still operate when the hood is open.

I think that whether you want to use a single or dual fans depends a lot on the shape of the condenser. ROLLGUY's condenser is rather square-shaped, and if he had used dual fans, they would have been too wide for the condenser, so some of the cooling power would be wasted. The single fan is taller than the dual fans, so it can cover more vertical space which the dual fans don't reach.

I think ROLLGUY made the right decision since the single fan covers more of the condenser than the dual fans would. However, on vehicles with condensers that are wider and shorter than his, dual fans would be a better choice as in that case they would cover more of the condenser.

Mxfrank · #18 05-04-2018, 02:02 PM

Quote:

Originally Posted by funola

Well made electric fans are very reliable to start with. Wiring 2 fans in parallel can hardly be called more complexity. 2 fans covers more surface area than a single large fan and provide better cooling. Together with the redundancy, it's an easy choice. 2 fans win hands down.

Two fans are only preferred when the radiator dimensions aren't close to square, or if there's a mechanical limitation which prevents using a single fan. In almost no case will two provide better coverage than one. Instead of hitting the keyboard, let your avitar take a pee and let's do the math together. Suppose you have an 18"x18" core, which is to say 324 sq in. Ignoring shrouds and mounts, if you cool that with an 18" fan, the covered area would be 254 sq inches. If you cool that with a pair of 9" fans, the covered area would be 127 sq inches. In reality, the numbers would be even less favorable, since there's no airflow through the hubs. Assuming a 4" flat motor, the hubs reduce coverage by 12.5 sq in for the single fan, and by 25 sq inches for the twin fans. So the twin fans would cover just 31% of the 324 sq in area, while the single fan covers 74%.

Suppose the core was 18x24, or 432 sq in. The single fan would still cover 254 sq in. But you could run dual 12's, which would cover 226 sq in. After adjusting for the hubs, the single fan still has an advantage of 56% to 46% coverage.

Total airflow would be comparable, as long as the motors were identical and the blades of similar design. But the airflow would be more concentrated with two fans. This may actually be a valid design objective, since most of the cooling happens on the inlet side. But that wasn't your argument.

In a puller configuration, if one fan of a pair becomes disabled, airflow through the core can actually reduce to zero, due to the working fan pulling air through the dead fan. In a simple pusher configuration, airflow is cut in half. In a Mercedes configuration, with a mechanical puller and an electrical pusher, one dead pusher fan of a pair will reduce airflow by more than half.

tjts1 · #19 05-04-2018, 02:34 PM

The single and dual fans use the exact same motor. The duals will move a lot more air. Pusher fans are never ideal compared to pullers.

funola · #20 05-04-2018, 02:41 PM

Quote:

Originally Posted by Mxfrank

(........) Instead of hitting the keyboard, let your avitar take a pee and let's do the math together. (.........)

I must have ticked you off huh?

ROLLGUY · #21 05-04-2018, 07:12 PM

Quote:

Originally Posted by Squiggle Dog

I went with the second generation W126 fan as well, in my W116. The fan shroud even has a 116 part number, so it looks original to the car. I've got one of your Sanden brackets with a new compressor and am currently working on converting the ACCII system to manual.

I upgraded to an 80 amp alternator and heavier alternator wire harness. I heard that the wire harness to the fan also needs to be upgraded and a different relay installed so the harness doesn't melt. I haven't researched that much yet.

I am following your other thread, and you are taking on quite a complicated project with the manual climate control swap. I am always encouraged by the work you are doing to your car. Keep up the good work! I have fan relays (runs the fan and compressor clutch from separate fused circuit) in stock if you need one, or you could build one yourself.....Rich

ROLLGUY · #22 05-04-2018, 07:24 PM

Quote:

Originally Posted by Mxfrank

Two fans are only preferred when the radiator dimensions aren't close to square, or if there's a mechanical limitation which prevents using a single fan. In almost no case will two provide better coverage than one. Instead of hitting the keyboard, let your avitar take a pee and let's do the math together. Suppose you have an 18"x18" core, which is to say 324 sq in. Ignoring shrouds and mounts, if you cool that with an 18" fan, the covered area would be 254 sq inches. If you cool that with a pair of 9" fans, the covered area would be 127 sq inches. In reality, the numbers would be even less favorable, since there's no airflow through the hubs. Assuming a 4" flat motor, the hubs reduce coverage by 12.5 sq in for the single fan, and by 25 sq inches for the twin fans. So the twin fans would cover just 31% of the 324 sq in area, while the single fan covers 74%.

Suppose the core was 18x24, or 432 sq in. The single fan would still cover 254 sq in. But you could run dual 12's, which would cover 226 sq in. After adjusting for the hubs, the single fan still has an advantage of 56% to 46% coverage.

Total airflow would be comparable, as long as the motors were identical and the blades of similar design. But the airflow would be more concentrated with two fans. This may actually be a valid design objective, since most of the cooling happens on the inlet side. But that wasn't your argument.

In a puller configuration, if one fan of a pair becomes disabled, airflow through the core can actually reduce to zero, due to the working fan pulling air through the dead fan. In a simple pusher configuration, airflow is cut in half. In a Mercedes configuration, with a mechanical puller and an electrical pusher, one dead pusher fan of a pair will reduce airflow by more than half.

Thanks for doing the math, I had no idea there would be that much difference in the two fans. Knowing this, I am glad I went with the single fan. My condenser is 20" wide X 16" tall. The double fans would not have put any air flow past the lower part of the condenser, and may have interfered with the hood latch. I think the double fan originally had a shroud that covered the lower part of the condenser/radiator (behind the bumper). I did not get the shroud, so that is another reason for using the single over the double. Again, I liked the fact that I was able to use the stock mounting with the single fan. It looks somewhat factory that way.

View Poll Results: Which fan?
Double W124 fan	5	55.56%
W126 fan	4	44.44%
Voters: 9. You may not vote on this poll