My m3 marlin is really struggling to keep cool when on the road. I have a front mounted kenlowe 16 fan on an aluminium race version of the polo rad which is on the small side but should be able to cope. The engine temp stays around 90 when going above 50mph, anything lower than that and temps creep up and the fan cuts in.

I know fitting a rad with more surface area should be my main focus but really without going custom there's nothing that will fit and work with my set up. I have ducted the radiator with some improvement and I have louvres on the bodywork to help get rid of hot air.

My next step is to try and move the radiator forward so I can fit the kenlowe as a sucking fan rather than blow, this would leave the front of the rad fully exposed to airflow, rather than having the fan blocking the whole surface area at the front. Before I go ripping it all apart is that a waste of time or a good step forward?

You have done all the sensible things but what engine and cooling plumbing arangement are you running?

Yes, get the fan to suck air through the rad. This made a helluva difference on my Locost. I used a 3 row ally rad too.
The trouble with blowing air through is, you get an amount of bounce back of air, which isn't doing any good at all. By sucking it through especially if it is ducted, no air is wasted.

Is the coolant rusty? If so you might find the coolant system needs a good flush.... You might have a neglected block...

So surprisingly I managed to get the rad fitted on the rear of the rad with about 5mm to spare... I had to trim the fan slightly to fit as the vanos unit on the m3 sticks out a few more inches than the standard lump, so here is today's progress;









The good thing is apart from turning some hose clips the install is completely reversible so I'm going to re duct things tomorrow and also change the rad cap as I could hear a slight hissing squeak when I turned to car off, which I'm
Hoping isn't the root cause of all the issues! I would kick myself if it was something so simple!

Can the hot air get out from the engine bay?

I had similar cooling issues with that engine - flushing with Thermocure made a huge difference for me.

Check any bleed off pipes are clear and flowing coolant , I've had a few cars over the years with cooling system problems due to no self bleeding. Do you have a heater or are the heater pipes blocked off?Rather than blocking off its better to biases with a length of heater hose possible fitting a bleed valve at the highest point of the system .
Is any air "ducted"through the rad rather than being able to get around the sides of the rad? Any air going through the rad needs to be able to escape the engine bay or else it will held in the bay restricting any cool air passing through the rad.. Fitting a larger rad may help as would a bottle of Water Wetter which can drop the coolant temperature by as much as 20 degrees, cheap enough to try ?

That fan layout is doomed I tell it is doomed. The fan is a major problem it is causing so much blockage due to fan exit being so close to the engine combined with general design of the fan.
The car would probalble run a lot cooler at slow road speeds with the fan removed. However a fan is needed. for traffic so a fan will have to go in front of the rad but that particular fan may be a Kenlowe but I don't think it is suitable for your application it masked just too high a percentage the rad area and the exit is so close to the engine it massively restricts the airflow.. Cheap aftermarket fans have a bad reputation so I would try a fan off small production car such as small Fiat.

I kind of had the same thoughts with having the fan so close to the engine. But i have not tried this set up yet so it's got to be worth a go before changing back to front mounted.

Either way I don't think it's going to work and may need to consider going down the Davis Craig water pump and controller route.

Any change to the coolant flow rate won't help in fact it may increase the temperature of the coolant entering the engine from the radiator. Essentially our problem is at slow speeds your engine is transfering more energy to the coolant per second than the radiator can transfer to the air. Because the cooling is adequate at higher road speeds it points to the air side of the rad. The only real cure for that is to increase the mass of air in contact with the radiator matrix by increasing the airflow rate or increasing the radiator cooling fin area.

The energy inputs and outputs to an engine and rad can drawn like so




It can be simplified to ignore the heat lost to the exhaust and by heat lost by direct contact with the air.

By drawing system imaginary system boundaries round the rad and engine we can analyse the heat flow in the radiator.






[Edited on 12/3/17 by britishtrident]

The rad performs with airflow over it, I know that as the fan does just manage to keep things under control. I have spent the day moving the rad as far forward as the nosecone will let me, this along with ducting hopefully should greatly increase the air flow to the rad, This has now opened up a bit of space. Behind the fan so it's not kissing the engine anymore. If this doesn't work I'm most likely going to have to go custom with my radiator