Electric Fans

P

Paul N

New Member
The next job ,my 1973 3500S had two fan fitted to the front of the radiator ,these were quite old and very noisy ,
I decided to fit two new 9" fans between red and engine ,unfortuneately temperature is going up halfway between normal and hot
this is now ,still in cold weather ,so in summer I think they would not be up to it .
I have now ordered a 14" fan ,so will use a 14" and 9" together ,
I will update the result.
 
You need to fit the biggest single fan you can and fit a two speed switch - take a look at my thread using a 16" fan. By sweeping the largest area of the radiator possible you massively increase the cooling efficiency. Using 2 fans is the wrong approach IMHO - work out the areas involved. A 16" fans sweeps 130% of a 14"....
 
PeterZRH said:
You need to fit the biggest single fan you can and fit a two speed switch - take a look at my thread using a 16" fan. By sweeping the largest area of the radiator possible you massively increase the cooling efficiency. Using 2 fans is the wrong approach IMHO - work out the areas involved. A 16" fans sweeps 130% of a 14"....
Click to expand...
thanks for the advice
 
1 or 2 fans depends on what you can fit in terms of radiator shape and size. eg 2 x 14" fans cover 53% more area than 1 x 16" fan - so if the rad is at least 14"high, and 28" wide, they would be better than a single fan. I have used SPAL (Italy) fans sucessfully, and they usually publish throughput (cubic ft/min) and current. Their shrouds come with blow open flaps to allow air flow separately from the fans running. My 74 S has the export fan+ viscous set up (includes shrouding on the core) and in temps up to 30C rarely moves off gauge centre, only when doing a decent climb, and then maybe 1mm to high side.
 
I bought a cheap one from a local supplier and it was awful, allowing the car to overheat if in traffic on a hot day. I then bought a Revotec fan of the same size (14" I think) and it works perfectly, even on the hottest of days, in the longest of queues. I have wired into the Aux side of the ignition so I can leave it on when I turn the engine off, like modern stuff does.
 
jp928 said:
1 or 2 fans depends on what you can fit in terms of radiator shape and size. eg 2 x 14" fans cover 53% more area than 1 x 16" fan - so if the rad is at least 14"high, and 28" wide, they would be better than a single fan. I have used SPAL (Italy) fans sucessfully, and they usually publish throughput (cubic ft/min) and current. Their shrouds come with blow open flaps to allow air flow separately from the fans running. My 74 S has the export fan+ viscous set up (includes shrouding on the core) and in temps up to 30C rarely moves off gauge centre, only when doing a decent climb, and then maybe 1mm to high side.
Click to expand...
Not quite. You have two voids at the center where the motors are instead of one.

And one of the lessons of the exercise was that actually the P6 isn't very hard to cool - the radiator is actually pretty good - the issue is the tightly packed engine bay when there is no air at all moving when sitting in traffic. Fix that and it won't overheat. You can run the car in high heat without any fan as long as you keep moving. Certainly at the 38 degrees I've run it at.

Any engine driven fan essentially works the opposite to what is needed. It's slow at idle and spins pretty much pointlessly at speed.

It's interesting in some ways it parallels performance PC when I were a lad. Back then people fitted screaming Delta fans, now massive, slow and quiet Noctua fans to cool CPUs.
 
I’ve found the same thing. It was at idle on hot days that the float chambers on my 2000tc would boil, never had an issue with the engine getting hot, even on track with 90°f days. Incidentally, I’m thinking of putting in an electric fan to free up a few ponies. So it’s a win/win.
 
I fitted a large Kenlow fan to my 3.9 - I think the biggest they offer. Its often used by the off-road Landrover guys who need a high spec fan when driving through mud and puddles, but remain at low speeds. The fan shroud is so deep, that I had to move the radiator forward about 1 1/2 inches (enlarge the slots on the radiator to chassis brackets. (engine driven fan removed)
Good idea to include a thermostat within the radiator for a switch and connect in an in-line fuse and relay as current draw is high (40 amp fuse). Power feed is from the starter motor.
It also helps to have LED indicators, as worst case day when wipers, heating and engine fan are running, the indicators were basically in-op.
 
Just thinking about the 2x14" vs 1x16" fan issue!! Theoretically the two 14" fans give a greater area but there is a lot more to it. I suspect the smaller fans are less efficient at pulling air so a direct area comparison may be misleading. Also the water in a radiator tends to flow across from top to bottom so a big fan in the middle of the radiator might be better directed at the hottest water flow rather than the two 14" fans which may be covering a larger area but over less hot parts of the radiator. Either way I am sure any set up will far out perform the original fan!!:):):)
 
It might be worth checking that the new fans are blowing the right way, have seen it before where people have had fans exhausting out of the engine bay towards the front of the car, with the resulting problems that this causes...
 
FWIW I used a dual range temperature switch and some relays to switch my 2 fans between series to spin at a low speed and parallel to spin at high speed as the water temperature increases just to cut down the power drawn, it works well but on reflection it would have been a lot simpler to just wire in a big resistor to get the low speed.
 
ratwing said:
FWIW I used a dual range temperature switch and some relays to switch my 2 fans between series to spin at a low speed and parallel to spin at high speed as the water temperature increases just to cut down the power drawn, it works well but on reflection it would have been a lot simpler to just wire in a big resistor to get the low speed.
Click to expand...
That's exactly what I did. it works well enough. In fact it's what manufacturers did up to the early 2000s. Now they have much more precise temperature control for emissions.
 
I originally fitted a 14" 120watt fan but that did not work.
I have replaced it with a 14" 220 watt seems to be working ,but not had warm summer weather yet
will see if the weather affects it
 
Re electric fans and switches - there are adaptors to fit switches in rad hoses available -
www.ebay.com.au

UNIVERSAL ELECTRIC COOLING FAN SWITCH WITH ALLOY HOSE ADAPTOR CHOICE OF 13-50MM | eBay

This thermostatic fan switch kit comes with a beautifully made, polished, billet alloy, fitting adaptor that allows the switch to be fitted into the HOT side radiator hose without the need to drill & tap or modify engine components. The switch can be used to turn any electric fan on & off...
www.ebay.com.au
and many switches, both single and two temp types, most common thread being M22x1.5 . When I had my radiator overhauled I had a threaded socket in that size fitted near the top.
 
Traditionally top, then the switch is sensing water temp out of the engine. I would go for an adjustable switch, not a fixed one.
 
I have a sensor in the top; thermostat is 83C, switch is at 89C. This is in an MX5 system, where the real gauge readings are 'Cold-normal-headgasket' because of suppression. When you have a temp gauge that reads true (rather than one that is suppressed to read normal most of the time) you can do some trials to establish what switch setting keeps the temp in a range you find acceptable. Make sure you find the cut-in and cut-out temps.
 
Last edited:
I had a boss mounted in the radiator side, top with a common thread size for commercial car rad thermostats - I think the current one is 83C. this gives the option to choose different thermostats until you settle on one (you can get some form of calibration with the switch-on and the car water temp gauge reading. I've only used the one and it kicks-in somewhere around 88C on my temp gauge.

But an adjustable one sounds a good idea - less hassle for draining and purging the radiator each time..
 
You must log in or register to reply here.
Back
Top