Fitting a larger cooling fan to R300 K Series

[brianjhall31]

Whilst I have no issues with maintaining a constant 80 degrees above 30mph and during track driving sessions I am constantly worried by how quick the water temp rises when in town traffic.  The fan comes on exactly when required by the thermal switch but it takes an age for it to pull the temp down again if I can't get sufficient forward motion i.e. stop/start traffic conditions.  On really hot days the fan runs constantly and the water temp only comes down when forward motion above 30mph regained.

Initial conclusion is that the current cooling system is insufficient to control a constant temp under the driving conditions that are more and more common today.  Don't want to jump into replacing the rad unless I have to.  Has anyone just upgraded the cooling fan to one with either a larger diameter or higher airflow rate?

Car is a has standard R300 K Series Thermostat (temp setting and position) with the Temp sensor in the modified position (not above the exhaust manifold)

I have not yet experienced and overheating issue but having the prospect is a constant concern as all my blats have to involve some time "parked" on the M4/M5 around Bristol!

[SLR No.77]

Brian, the situation you describe is quite normal even with the senders repositioned, with little or no airflow over the radiator the temperature on the gauge can rise a little. You could fit a bigger radiator but it will only be effective if it can radiate enough heat at low or no speed without the fan running to enable the thermostat to close a little and start controlling again ... and that might need to be a pretty big radiator, that's why there's a fan fitted.

In reality you're observing the difference between the thermostat controlled temperature when the coolant coming from the radiator is cooler than the engine, and the wide open thermostat temperature with a hot radiator just before the fan kicks in. If you could change the fan control setting you could close this differential, for example with a programmable ecu controlling the fan rather than top mounted sender ... the other alternative is to fit a fan override switch so that if you're stuck in traffic you can bring the radiator temperature down a little, if nothing else just for peace of mind.

Stu.

[SM25T]

What is the setting of your thermostat. Mine came with 88C, and I changed it to 82C. The fan switch may be rated on at 92C and off at 87C ? Easily changed.

[timb2117]

Have to agree with Stu in the first instance, I tend to go belt and braces.... I did a post cant seem to find it, but essentially here in Australia it does get a bit hot, with the 1800 K 'history" I chose to go a bit OTT.;

So nice new radtec with side tanks, from demon tweeks, ducted the air at rear of rad with carbon fibre panel cut to fit (thanks Ebay) and a big fat separately manually wired fan on front of rad....My idea is at end of track sessions hit the extra fan - in traffic same.

When on it boosts the airflow considerably and she gets back down to acceptable faster. Bear in mind though the trade off of in effect of having the extra hardware in front of the rad when its turned off which does cut airflow a bit....

[7 wonders of the world]

Look at the fan switch first as these are readily available with a wider temp range - quick and easy switch, also check it corresponds to your stat - 

and then look at a larger fan if your still concerned, it you can maintain temps under full beans blatting then you only need additional airflow in traffic.

I only run a 9" fan with the parameters set correctly i the Emerald no issues in traffic.

[revilla]

You don't have a triple-pass radiator do you? The water pump seems to push much less coolant through these at idle and they can tend to run hotter than normal in traffic.

[brianjhall31]

Thanks for all the good comments and advice.   To clarify some of the points, currently the set up (apart from the repositioning of the temp senders) is "as delivered".  Standard Rad, ECU and Thermostat etc.

When running above 30 mph temp remains constant at (gauge indicated) 80 degrees.  Drop below 30 mph in traffic with stop/starts and it creeps up to approx 90 degree but will come back down if forward movement can be regained and, if above 30 mph will come back to 80 degrees without fan activation.  If stationary for more than a couple of minutes fan comes on (92 degrees?) and remains on (unless ambient air temp is below 15 degrees) until some forward motion can be achieved.

All makes me think that the current fan has insufficient airflow to compensate for the loss of normal forward movement flow thru the rad and, on the occasion when the ambient air temp is 30+ degrees (like recently), a stop/start traffic situation will not be controllable by the current set up.  In aerospace terminology we call this "coffin corner"

[John Vine]

Just a wild thought...

I take it the fan is wired correctly to spin the right way? 

JV

[SM25T]

Good point John. I saw a new build at a Swiss meeting where the fan was mounted behind the radiator but blowing forwards. Easy fix by swapping wires to fan motor.

[brianjhall31]

Just put a jump lead across the fan activation switch.  Confirm it is correctly wired and pulls air thru rad.  Removed the fan and tested with 12v, seems pretty asthmatic for job required.  Going to check the Spal specs......... 

[timb2117]

Also from my little knowledge seriously consider ducting the air, what I read stated that the fan (lets say 8') only pulls air across the fins directly in front of it so pie r squared the 8' (oops trying to sound clever should know better) whereas if you duct so that the only air getting through must pass over the fan it is in effect drawing air from across the entire fin range.

- S'pose another way of thinking is that the manufacturers only waste valuable engine bay space for good reason when they fit dirty great big plastic rad cowlings.... 

[R300 FNL]

Timb2117 - I have a radtec radiator with the fan on the back, is it easy enough to mount a larger fan on the front? I didn't think there were any mounting points on the front?

Do you have a link to the fan you fitted?

Thanks

[timb2117]

Here you go essentially angle alloy straights filed to fit round profile of fan surround, then carefully! drilled bottom of rad surround to rivet on, solid as. rear fan cowling sheet carbon, but alloy would do, cable run to relay near ecu and switch on dash, about half day if you do it super carefully for nice finish, still not super happy with carbon

joint must remake one day...

[oilyhands]

The phenomenon is exacerbated by relatively poor  efficiency of the coolant pump at low engine speeds. Whenever I warm up an engine following an upgrade the temperature tends to soar with the fan engaging and staying on, the recorded temperature stays quite high seemingly indefinitely. If I hold the RPM at round 2500 for 10 seconds or so the temperature starts to fall back and the fan stops running as the coolant circulation is much higher.

Oily

[Wrightpayne]

So basically hold it at 3k revs while you're in traffic :-)

I was doing some research (googling) for a fellow club member trying to identify the fan switch washer size and the switch is quite a common part used in lots of tintops. Caterham parts website uses the manufacturers part number rather than Caterhams own, making the part easier to identify via google. Should help if you are looking for different temp switches.

[SLR No.77]

Oily, just a thought on this, could it be that at tickover the bypass is flowing "relatively" more coolant compared to the main circuit? There's limits to the level of flow that can pass through the 16mm hose compared to the main circuit and as revs increase the percentage of mix from the radiator circuit might increase? Just a thought!

Stu.

[oilyhands]

Stu, that can be a factor especially with TBs where there can be a lot more flow through the de-gas spout. Improving radiator efficiency and cooling capacity is all very well, but if you are not effectively circulating the coolant, the engine temperature (measured at the rear of the head) may not reflect this. Restricting the flow through the bypass radically my help.

Oily