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Fitting electric radiator fan


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Yes I should mention mines a 5. No shroud, Even when the radiator was on the way out its still dint boil and as I have written several times due to a leaky bottom hose I drove it through town with no water in the radiator and thanks to the oil cooler didnt blow the head.

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Hi All

 

Interesting Video from Freiburger, who i remember well from the days when MotorTrend was FOC, esp the Roadkill episodes, much fun.

 

Now i'm going to assume the fans on a 350 Chevy engine are a little bigger than a TR6 take use more power to run but 30bhp is alot.

 

Take 30bhp off our 150 (lol) and its way down.

 

Hopefully its more like 15 to 20 but of course thats off more like 135, if your lucky.

 

So yep a good reason to go electric.

 

I had Autosparks add the electric fan wiring ito my new harness but possibly wasn't going to use it but maybe now i'll think again.

 

Wonder which is best?

 

The Revotec looks the neatest in terms of brackets etc but i don't know about reliability, which is of course most important thing.

 

Cheers

 

Keith

Edited by Keith66
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Not wishing to confuse but Revotec fan is a Comtec fan and very good too. I bought one, the fan that is, from them and fitted it on some brackets. Unfortunatley I had an overheating issue and had already bought a new radiator......the fan has never been used as the car has never gone past the half way mark on the temp gauge....in 3 years ...and no I didnt remove the original. So tend to agree that the original on a sorted cooling ssystem seem to be fine.

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Hi Keith,

I have the same harness with electric fan option.

You will have 4 wires for this in the engine compartment, to be fitted to the relais.

I looked at the Revington de luxe kit, but will buy a decent fan and brackets (probably from Revington) and a temperature swith that I install in the steel pipe.

Revington sells these too.

I do not want the controller, a simple switch is more reliable, and also less visible.

So I will buy:

14 puller fan with brackets (tie wraps are not my cup of tea)

Switch (I have not decided yet which temperature range)

Relay

I already have the water pipe with threaded boss and the fan bolt and spacer.

I will not install the original fan, so my TR will be 150+30=180 hp (not).

 

Regards,

Waldi

 

Hi All

 

Interesting Video from Freiburger, who i remember well from the days when MotorTrend was FOC, esp the Roadkill episodes, much fun.

 

Now i'm going to assume the fans on a 350 Chevy engine are a little bigger than a TR6 take use more power to run but 30bhp is alot.

 

Take 30bhp off our 150 (lol) and its way down.

 

Hopefully its more like 15 to 20 but of course thats off more like 135, if your lucky.

 

So yep a good reason to go electric.

 

I had Autosparks add the electric fan wiring ito my new harness but possibly wasn't going to use it but maybe now i'll think again.

 

Wonder which is best?

 

The Revotec looks the neatest in terms of brackets etc but i don't know about reliability, which is of course most important thing.

 

Cheers

 

Keith

Edited by Waldi
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It's really hard to extrapolate what HP you are loosing. It is a function of the amount of air moved and the efficiency of the fan moving the air. Which in turn is related to the number, pitch and aerodynamic efficiency of the blades and the speed of rotation. . All very complicated.

Interestingly there were fans in the distant past that "feathered" over a certain speed. Trouble is I think they often snapped and Impaled themselves through the bonnet. At least it gave you a visual indicator that the fan had failed..

Cheers

Tim

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The empirical tests showed that 18 inch fans sapped 14-30 HP from the test engine at 5000 RPM. The "feathered" fan was good for a 24 HP loss.

 

I think fans on the TR6 cars were 14.5 inches (at least on a '74). As you suggest, predicting the losses from a smaller fan based on those from a larger one is complex. Third, fourth, and even higher powers sometimes show up in air fan equations. A simple square relationship would suggest that our smaller fan's losses would be in the range 9-20 HP. Assuming a fourth-power law would put the range at 6-13 HP.

 

Maybe someone out there knows better what the scaling looks like for fan diameter.

 

Ed

Edited by ed_h
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One of the things I think I noticed as soon as my first drive without the crank driven fan was that the engine seemed to loose less speed when I disengaged the clutch and let up on the gas between gears...I attributed that to the total lack of fan blade drag or resistance.

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Well said Jochem.

I still remain convinced that an electric fan is no big deal.

Totally un original, just another thing to go wrong, more money, more work and as someone who lives in a hot climate and drives hard and in traffic, I can testify its just not needed.

Just keep your system good and if you like fit an oil cooler that was an original option.

So it was about 30°c with sunshine today and I took my 5 for a burn and thought I would see. So at 2000rpm driving it was at about 1/8th and after the burn I left it parked, motor running a couple of minutes and it went to 1/2. No electric fan and my lower radiator hose leaks ever so slightly too as the steel pipe needs better pushing in. So I think its all down to a reliable well flushed system.

don't get your hopes up too much....max. HP improvement switching from mech fan to electric fan is 1 HP ! At least not the reason to switch to electric.

 

Jochem (with electrical fan)

Edited by Rem18
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don't get your hopes up too much....max. HP improvement switching from mech fan to electric fan is 1 HP ! At least not the reason to switch to electric.

 

Jochem (with electrical fan)

 

Jochem--

 

Can you direct us to some background or support for that statement?

 

I'm not necessarily challenging it, but we have seen some fairly convincing information that suggests the difference can be much higher.

 

Ed

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Yes interesting but I think the logic is in the hp needed to cool.

Its fairly simple physics. If you need 1hp to cool the rad then it stands to reason that electric or mechanical will probably use same to achieve same or if not the mechanical fan would have cars running at -30°c if they are 10 and 15hp like some fan manufacturers claim. Sure when running at 100mph a fan is off and better, but as I have said when an electric fan goes pop you might have to stop driving.

I suppose you could try a rolling road test with both fan on and fan off, but I remain convinced that there are not all these differences and as I tested yesterday a fan is not needed if your system is efficient.

So do you want an electric fan for cooling (if so not needed) or Hp (yet to be proven)? Certainly not for reliability or originality...

Edited by Rem18
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I think that, when you're using any appreciable HP, the resulting forward motion will be sufficient to cool the rad, outweighing anything a fan would give - mechanical or electric. I think it's when you slow down that you need a fan. The compromise of a mechanical fan is that the designers want enough cooling at idle but not sap too much engine power at high revs. An electric fan doesn't have that compromise. But it has a different one if it's only triggered by coolant temp. Under-bonnet temperatures can climb, even though the engine temp is fine. The intermittent action of the electric fan means the mechanical wins in this respect.

 

Does anyone remember - I'm sure I've seen this written down somewhere - how many HP the viscous coupling is claimed to save? 2HP? 4HP? It was something like that.

 

Cheers, Richard

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In a pure sense the electric fan uses more power i.e Mechanical power from the engine is converted into electrical power by the generator. This is then applied to the electric fan where it converts the electrical power into mechanical power. Whereas the mechanical fan is run straight off the engine power. Any power saving is achieved on the length of time the electric fan is not in use.

 

The advantageous with the electric fan is it's off during the engine warm up time and hence there is a shorter warm up period. No over cooling in the winter. And if you fit a larger fan than specified there should be better cooling when stuck in traffic.

 

As an aside I have tried the three versions of plastic mechanical fan fitted on six cylinder engines to the Mk2 2 Litre and the 2.5 Litre engines, and found no advantage in any of them. They all gave the same results when stuck in traffic and driving.

 

Dave

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Its still all very interesting. In theory the thermostat takes care of warming up time. Still bet you if you measure it the hp is like 2-4hp as Richard states. Sure iits on the web somewhere or someone will have dyno tested their car with and without?

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An analogy to the slower warm up with the mechanical fan is akin to heating your house in the winter with the windows open. Yes the thermostat will try to cope but it will take much longer to reach the required temperature and use more energy to do so.

 

As for the electric fan being more efficient than the direct drive mechanical type, once you start converting energy you incur losses. The gains are achieved when the electric fan is not in use. A modern cooling system has a larger capacity rad which reduces the periods the electric fan is working. Hence, a more effective system.

 

Dave

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Dave. Certainly there is a power saving when fan is off (rather like the A/C pump on a car cutting in) and to be fair that a lot of time, I hadnt thought much about your reference to the fact that a TR system wasnt really designed for a fan and its a good point. So basically you can save a couple of HP while the fan is off but generally I guess you want that Hp when booting the car so the fan will be back on then. Interesting to see how much a fan might come on in a TR compared to more modern systems?

Edited by Rem18
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The electric fan on my 4A never comes on while the car is in motion and I have been in some very hot temps in South of France and California. I usually switch the fan on manually in standing traffic which keeps the underbonnet temp down.

 

Cheers

Graeme

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We lack (emperical) data, but we can still make an estimate...

 

Electric fan:

The electric fan which draws around 10A, has an electric power consumption of 10 A x 13V = 130 W, but the generator has an efficiency too, so the mechanical power consumption from the engine crankshaft (including the generator and fan belt losses) will be say 150W (approx. 0,2 HP). It is only needed at lower speeds (in traffic jam etc), and will run say 50% of the time only then (off course depending on engine condition, ambient air temperature), so the net required power is 0,2 * 50% / 0,1 HP for contiumuous cooling at idle.

The efficiency of an electric fan will be better than the standard fan, since it has a shroud to minimize re-circulation, and it runs at a much lower speed, which improves volumetric efficiency.

 

Mechanical fan:

The standard mechanical fan (driven from the crackshaft) has a (very) poor efficiency to start with :

It does not have a shroud, which increases recirculation

It is some distance from the radiator so there is even more recirculation, which costs extra power (or reduces efficiency).

Fan (volumetric) efficiency also reduces with fan speed.

Power consumption increases to the 3rd power with speed (engine RPM), this is a law of physics.

 

Comparison:
Now if we know the mechanical fan is capable of cooling the engine at continuous idle speed (say 1000 rpm for this analysis), we can safely assume it will also absorb around 0,1 HP at 1000 RPM (a bit more due to its poor efficiency and a bit less since no energy conversion via the V belt and dynamo is required which also costs power) , but we lack data for a better guestimate.

As fan power increases to the 3rd power with fan speed (rpm), the power absorbed by the mechanical fan at....

3000 rpm will be around 2,75 HP (0,1 * (3000 / 1000)3 )

4000 rpm will be around 6,4 HP (0,1 * (4000 / 1000)3 )

5000 rpm will be around 12,5 HP (yes, do the math)

 

Regards,

Waldi

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