mcramsay
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| posted on 5/2/17 at 09:21 PM |
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Rad fan running when driving slow
So just got my BMW M3 powered marlin sportster out for its first drive today, I noticed whilst under 40mph the cooling fan had to click on to cool the
car down. Fan comes on at 98 and goes off at 94. It's a big kenlowe fan that pretty much covers the whole front of a polo aluminium racing rad
which should be man enough for the engine.
This prompted me to look at the workshop manual for the m3 as I thought I had the fan cut in too low however the thermostat opens at 80 and the stock
fan should cut in at 92. If I now lower my fan temp it's going to be running constantly. The fan is able to control the temp fine and it's
not the the engine is boiling over however air flow at 30-40 mph should be more than enough to cool the rad
My thoughts are that the fan is covering so much of the front of the rad no airflow is actually going through the core, combined with quite a fine
mesh grille that might be restricting airflow...
Any other ideas of why this might be happening/how to sort
As as said this was my first road test, previously the car has sat idling getting to 98 degrees and dropping to 94 by fan control for 2 hours
completely happy so I'm not looking down the head gasket route or anything like that!
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gremlin1234
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| posted on 5/2/17 at 09:30 PM |
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is the fan coming on, or just rotating in the airflow, ( and generating enough power for a fan indicator light) ?
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mcramsay
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| posted on 5/2/17 at 09:46 PM |
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The fan is powering on.
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coyoteboy
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| posted on 5/2/17 at 11:13 PM |
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Can't see a polo rad being man enough for an M3 engines basic output. The fans coming on because the rad isn't cooling enough at low
speeds.
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Ben_Copeland
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| posted on 6/2/17 at 07:05 AM |
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Same thoughts. Doubt the polo rad would be man enough, my civic rad which is about same area as polo isn't really enough for my 2l turbo
Ben
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Hornet
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| posted on 6/2/17 at 07:46 AM |
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My fan is behind the rad. To allow air at rad. Can you do this or no room?
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cliftyhanger
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| posted on 6/2/17 at 07:59 AM |
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Looks like a larger rad is required.......
I had an unusual one on my old Triumph Toledo when I fitted a polo rad. Faster I drove the hotter it ran, the car design just wasn't getting
enough airflow through the rad for the 100bhp engine I had fitted. I either had to re-design the front end, or find a larger rad......(found a passat
rad that fitted, and works a treat, 30% more area and cost a whopping £25)
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rodgling
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| posted on 6/2/17 at 03:07 PM |
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I had progressively worse and worse issues with cooling (also on an M3 engine). Eventually I did a coolant flush with 1qt of Thermocure and it is
miles better now, even with an oil cooler blocking half of the radiator. Maybe worth a try as a cheap/easy first step.
[Edited on 6/2/17 by rodgling]
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adithorp
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| posted on 6/2/17 at 04:32 PM |
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If the cooling is fine under load/at speed but not at low speed/load that does point towards an airflow issue.
What mesh do you have? I know you said fine and thats what makes me wonder. If it's expanded ally type, then I'd start with changing it
for woven mesh. Expanded ally mesh has very poor airflow (it's little more than slit holes in solid sheet)and the finer/smaller the mesh, the
worse it is.
Also where does is your fan switch possitioned compared with where the it was in the original BMW install? If the BMW was in the rad and yours is in
the top hose for instance then there will be a descrepancy between the on/off values required.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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ian locostzx9rc2
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| posted on 6/2/17 at 05:07 PM |
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As said firstly remove the mesh grill and see if it makes a difference if it is a fine it will block the flow a huge amount if the switch position is
correct for the engine you may have to buy a bigger capacity polo alloy radiator .
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mcramsay
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| posted on 6/2/17 at 05:46 PM |
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The polo rad isn't just a bog standard one, it has the thicker 55mm core, to be honest I researched this immensely and it was the only one I
could find that would fit in the space. When the fan comes on it only needs around 8 seconds to reduce the engine temp by 4 degrees which says to me
the rad has the capability to cool the engine with the correct air flow... I agree it could be bigger but I have literally no room. I did a little
test holding a hair drier infront of the mesh, I can hardily feel anything coming through to behind the rad, so I think I run with the mesh off might
throw up some different results... also the m3 engine is supposed to have a viscous fan fitted, perhaps if I can squeeze this back on it may help
things??
If the above don't work then I'm out of ideas...
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coyoteboy
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| posted on 6/2/17 at 06:16 PM |
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Aye, you're stuck with the size you have. My point was that it's going to be a close call so you need to pull out as many restrictions as
possible, but you knew that already 
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mcramsay
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| posted on 6/2/17 at 06:40 PM |
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I think I can get it working, if not a Davies Craig water pump/ fan controller might be the only option
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BenB
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| posted on 6/2/17 at 06:52 PM |
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What's the problem with leaving it as it is? It sounds like you've got a big old fan which is doing it's job when passive airflow
isn't enough.
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BenB
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| posted on 6/2/17 at 06:55 PM |
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Would Redline Water Wetter help here???? Improves heat transfer- my gut instinct is (if the blurb is correct) it helps heat dissipation which should
mean for a given size radiator you get better heat leaving the rad.
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Camber Dave
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| posted on 6/2/17 at 06:59 PM |
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Do you have vents in the bonnet top or sides?
It is a hell of a job trying to force hot air down, round the engine and out from under the car.
Quote
"As as said this was my first road test, previously the car has sat idling getting to 98 degrees and dropping to 94 by fan control for 2 hours
completely happy so I'm not looking down the head gasket route or anything like that!"
Was the bonnet fitted during this test?
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ian locostzx9rc2
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| posted on 6/2/17 at 07:46 PM |
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Different mesh grill hopefully will sort it
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mcramsay
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| posted on 6/2/17 at 07:48 PM |
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Bonnets were fitted on the test, there are no louvres in the bonnet but there are many down either side of the car, but I agree bonnet louvres would
help, I've not heard of water wetter before but it's worth a try! I am going to fit a makeshift fan running light and go for a 50 mph run
and see if I'm getting cooling issues at speed or only when town driving, that will shed more light on the way forward
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