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Reversed Cooling Fan

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RJS

RJS

Jedi Warrior
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Hi,

After 10 years, I just noticed the PO mounted the cooling fan on my engine backwards. This is an OEM stock TR4A fan. The fan blades are still pitched to pull air through the rad but, the curve on each blade is facing the wrong way. I'm sure this reduces the fan's efficiency/ effectiveness but, curious if anyone can say by how much?

I've never had any cooling issues with the car but, I am planning to flip the fan around just to get it right.

Thanks

Bob
 
Bob -

If the fan is pulling air thru the rad now isn't that how you want it? By reversing the fan won't air then be pushed out of the rad, basically pushing against the outside air wanting to come thru into the rad?

Dave
 
Bob,

Here's a picture of my unrestored TR4A where you can just make out 2 of the blades of the fan and which I believe is correct based on pictures from the workshop manuals.

dcp_1773.jpg


I thought the fans just had pitch so I'm a little confused by what you mean regarding pitch versus curve. Have pictures? :smile:

Scott
 
Musicman said:
Bob -

If the fan is pulling air thru the rad now isn't that how you want it? By reversing the fan won't air then be pushed out of the rad, basically pushing against the outside air wanting to come thru into the rad?

Dave
Click to expand...

Mind games, Dave. If you mount the blade "backwards"on the pulley/motor/whatever, you still have the blades "attacking" the air at the same angle. But if the blade is curved, it will be less efficient. The only way to reverse the flow is to reverse the direction of blade rotation.
 
Yes, it is somewhat counter-intuitive that reversing the mount of the blade has no effect on the direction of flow.

You say "This is an OEM stock TR4A fan" then mention it's curved? The above pic shows a TR4A with a metal fan (like a TR4) that has a pattern but not sure I would call that curved.

The thing is... some folks fit later fans (e.g. from a TR6) to the earlier cars. Depending on a number of factors I believe they sometimes have clearance issues. One solution to clearance issues may be to reverse the fan. Not ideal aerodynamics but it does work.

Or maybe the PO was a blockhead.
 
Oh wait, I think maybe I understand after looking at the picture of my fan blade again! At the edges of each blade is a small curve which faces back toward the engine. If the fan is mounted backwards, the pitch would stay the same but those small curves would face the radiator now.

Is that what you are referring to Bob?

Scott
 
Hi

Just finished cutting the lawn. Mickey, Scott, you guys nailed it. It's counter-intuitive but, the pitch on the fan blades is still correct to pull air even when mounted backwards. All it means is that the small curves on the leading and trailing edge of each blade (just like in your photo) are now facing the radiator. Think of the curve on an airplane wing creating lift (push) downwards. Same principle.

I plan on flipping it around but, it will entail removing the radiator so the fan bolts will clear.

So, any guess as to how much efficiency am I losing by having these edges facing towards the rad?

Bob
PS: those tabs facing the rad also make the clearance to the rad so tight it is nearly impossible to replace the (wide) fan belt w/o bending some fins on the rad (ask me how I know).
 
RJS said:
It's counter-intuitive but, the pitch on the fan blades is still correct to pull air even when mounted backwards.
Click to expand...
If it didn't work that way, then you would have to worry about which way a nut goes on a bolt!
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]So, any guess as to how much efficiency am I losing by having these edges facing towards the rad?
[/QUOTE]Not enough to measure/notice.
 
RJS said:
...I plan on flipping it around but, it will entail removing the radiator so the fan bolts will clear...
Click to expand...

Trivial on a '4 (compared to the same task on a TR3) -- there is so much room there you might even get away with loosening the lower bolts and leaning the rad forward... but might as well pull it for a nice flush.

OTOH -- if it isn't getting too hot at idle and the look doesn't bother you then maybe it waits until things are apart for something else (and there will always be something else).
 
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