The Triumph Dolomite Club - Discussion Forum

Hi all

I hope you are all enjoying this nice warm weather, in Europe anyway , I am looking to remove the energy sapping engine driven fan and fit an electric one in its place on my sprint, please can you tell me which one is best for me to fit, does it come in kit form, is it a suck or blow type fan and does it fit on the engine side or the grill side of the radiator.


I would also like to fit the water temp switch sensor in the cooling system would you fit this into the large pipe coming of the top of the radiator or the small one on the other side of the radiator, and what size fan belt would I require.


Thanks for your help again look forward to receiving your answers

You posted this at just the right time for me.
My very next purchase to get my project moving along.

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Trevor

75 Sprint in Magenta called GunGaDiN GGD944N
2017 Jaguar XE R-sport

I'm hoping to do this too, see my thread on belt size. I would use a Revotec thermo switch in the top hose. This is the one https://www.demon-tweeks.com/revotec-el ... src=aw.ds You just select a size that suits your hose diameter.

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

Notwithstanding the issue of the bottom hose being the best place to determine, from a simple threshold temperature measurement, whether the electric fan needs to be on or off (a different issue from any nugatory attempt to actually control engine temperature with a fan), there are far cheaper ways to do this.

I'm using an NTC sender that was £4 off eBay in a hose adapter that was a fiver off Aliexpress and a simple voltage comparator module with a built in relay like those that are £3.45 off eBay (mine's a two channel one that was supposed to have on/off hysteresis, but due to an issue in translation turned out to be 4 comparators used as a window controller - but we have a drill to fix the PCB with).

The comparator lets me set an on temperature (currently from about 40 to 120C, but I may narrow that a bit) with one pot. But I have modified it so another pot sets the off temperature as an offset to that, which can be as little as zero offset. But that's arranged so it doesn't change the on temperature. Those mods cost me another sick squid - but I have 2 pots, 24 diodes, and about 290 1/4 watt resistors left over.

I've mounted the module and two pots in a box (which came from Maplins and I think cost more than any other single item), which is currently double sided sticky taped to the front parcel shelf so I can set it up. I still need to add a cap to kill the noise picked up in the lead to the sender jittering the relay at low hysteresis. And when it stops raining I may re-cable with screened twinax rather than the twisted pair I have in.

There is point on this issue about the mechanical fan taking power more or less all the time. That is that once the airspeed of the car is greater than the pitch speed of the fan blade, the angle of attack between the blade and the airstream stops being positive, and it switches from transferring power into the airstream to taking power out of it. I'm not sure what that speed is for the mechanical fan and torque drive, but it's possible to estimate that for an electric fan from its CFM value (if you have one that's true) and its CSA - the zero angle airspeed should be fairly close to the free airspeed the fan gives.

That angle of attack limit to the airspeed that a (more or less) constant speed electric fan can have an affect within (and the square root relation between the convective thermal coefficient of air and airspeed limits its effective range further) is one of the reasons engine temperature control still needs the thermostat, and the fan can't really take over that job.

Graham

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The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

Reading the above makes totally clear why I use a revotec also...

Jeroen

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Classic Kabelboom Company. For all your wiring needs. http://www.classickabelboomcompany.com

I have read and re-read Graham's fascinating post and I still couldn't do what he describes. Mostly because I've no idea what he is talking about electronically.

However, the point of my post is to say that on Thursday (remember Thursday the hottest day ever recorded in England), on that day I drove my Dolly 1850 from Scotland to Silverstone, a distance of 380 miles. It was HOT and I was absolutely knackered with my shirt wet with sweat. BUT even when stuck in crawling traffic the car was perfectly OK and the temp gauge hardly rose over the central normal position. It didn't boil and it didn't lose any coolant. The point is it still has the original engine driven propellor (fixed not viscous) and it just goes to show how effective it is when everything works properly. Mine has a re-cored radiator and a new water pump, so is as good as new in the cooling department.

I think I'll just leave the mechanical fan alone. As for the lost bhp, what you've never had you won't miss. The old girl still did 34 mpg at motorway speeds.

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

But where's the fun in that?

And if you've already made the decision to switch the electric fan on and off from the temperature in the top hose, why would you use anything more complex than a simple thermal switch anyway – as I understand it, the temperature in the top hose at which to turn on the fan is determined by the thermostat you’ve got. Apparently, that's 12 to 18 C above its opening temperature, according to Stoney racing. That seems credible. I think it should be somewhere below where the thermostat is fully open, less about 4 or 5 C for the overshoot that happens while the water cooled by the fan works around through the engine at idle. So it don't need any adjustment unless you swap thermostats twice a year. And even if you do, you can swap switches at the same time and still be squids in.

It's just that I can't see how the top hose temperature, as controlled by the thermostat, can be a good indicator of what's happening in the bottom hose, given how slow all these processes are when viewed from an NTC sender in the coolant. And that's compared to even how slow the thermostat is. Whereas the temperature in the bottom hose will go up and down well before the temperatures in the top hose, and by much more. So its a far better indicator of whether the electric fan should be on or not. So switching there has got to reduce overshoot, and may reduce undershoot if that really is a problem.

I don't doubt the ready built controllers that are available will have enough range to be used in the top or bottom hose. But they are a bit expensive given the sender, hose adapter, and basic comparator with a 20A relay on board are not much more than £10 the lot (and 2-3 weeks lead time from China) – the cost of putting accessible controls in the cab, as another toy to play with, is separate.

And I want to be able to set the off temperature separately from the on, because I'm bothered about minimizing the power drain when stuck in slow traffic in the dark and the rain. So I want them as close together as possible - though it does seem they can't be the same without the relay jitters (but I'm not beaten yet). But that's a nearly trivial mod if you can desolder and solder components on a PCB and cut the odd track or two. But okay, I've been mucking with electronics since a "4 valve" was 4 EL34s in a 100 watt guitar amp. So my view of trivial may be skewed. So I've been looking at the idea of just adding some components around the outside of a stock comparator, which might be easier.


Graham

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The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).