Electric fan protocols and temperature points

ghce

ghce

Well-Known Member
Hi, am planning to install an electric radiator fan but am not sure what temperature points for switch on and what should hysteresis range should be, also if multiple speeds are appropriate. Another consideration would be the relationship between thermostat and fan if the thermostat temperatures are changed.
I have no trouble with making an electronic variable temperature control for fan turn on/off. Are there specific guidelines or automotive industry standards I should be adhering to.

Graeme
 
Is there any established best practice out there? - probably not. Common sense goes a long way here. First off, both switch on and switch off should be above the thermostat operating temperature. Next, and probably most important, the fan should be wired to be live after engine switch off to allow for heat soak after running. After that each engine and installation is different and needs its own solution. Since we are running carburettors, which don't have an inbuilt compensation for engine temperature in the way modern EFI systems do, it would be nice to maintain the engine at a constant temperature irrespective of operating condition. That way the fuel mixture, once set, would remain correct at all times. Theory therefore suggests a graduated fan speed response to climbing coolant temperature over only a couple of degrees. But can your fan and operating system deliver that? And how to choose your optimum temperature? For that I personally would start by having a test run with the engine driven fan still in place and a multimeter across your temperature sensor. Look at the sensor output (resistance, whatever) for an instrument panel temp guage reading that you know the car has been happy with in the past and use this as your switching datum. This exercise will also give you information as to how much sensor variation reperesents a shift of the car temperature guage into areas you are not happy with - both hot and cold.

Many yeaars ago I fitted a BMC 1300GT (the one with the productionised Cooper S engine) with a front rad and an Alfasud electric fan. I switched the fan manually. It was surprising how much extra performance and economy was liberated by allowing the engine to run significantly hotter than normal. There again, on one very famous high speed run I overdid it a bit and arrived at destination with the lub oil having exited between head and block and then having escaped out of the sides of the bonnet and now plastered in an eye catching brown streak down the full length of the sides of the car. Amazingly the head sat back down of its own volition and there were no consequential problems! The luck of youth eh! So be warned there are hazards to the game!

Chris
 
ghce said:
Hi, am planning to install an electric radiator fan but am not sure what temperature points for switch on and what should hysteresis range should be, also if multiple speeds are appropriate. Another consideration would be the relationship between thermostat and fan if the thermostat temperatures are changed.
I have no trouble with making an electronic variable temperature control for fan turn on/off. Are there specific guidelines or automotive industry standards I should be adhering to.

Graeme
Click to expand...

I have seen some rally parts available which include twin 10" fans and non adjustable thermo switches set at turn on at 90C and turn off again at 80C.

I am interested in these as the switch is set into a tube which fits in your top hose (the top hose is cut and the stainless tube jubilee clipped into it) unlike the stupid kenlowe way which is almost impossible to seal.

Not adjustable though?
 
If you have no problems knocking up the circuitry then I would be tempted to use either the standard temperature sender, or add another proper sender into the thermostat housing, that way you're measuring temperature at the head rather than in the rad, also this would probably be a neater solution than probes in pipes etc.

A pulse width modulated variable speed fan control wouldn't be hard to make at all, on the basis that you are trying to obtain a constant temperature it may be good, so the fans start spinning slowly once the temperature goes past thermostat opening, and ramp up until full speed is attained at about 90 degrees, maybe a little less. It's probably quite a narrow operating range, maybe that's why you don't see it often.

Interestingly I may be doing the exact same thing on the wifes 216, as somebody has bypassed the ecu fan control and fitted a manual switch on the dash, which I think is a bad idea especial with the wife driving (how's she supposed to know when to turn it on and off ?)
 
I am interested in these as the switch is set into a tube which fits in your top hose (the top hose is cut and the stainless tube jubilee clipped into it) unlike the stupid kenlowe way which is almost impossible to seal.

Not adjustable though?
Click to expand...

There is an adjustable type available see demon tweaks
 
The hose insert type is £40 from Burton power so making one is probably the cheaper option. Could you post up instructions on how to make one please Webmaster?
 
webmaster said:
A pulse width modulated variable speed fan control wouldn't be hard to make at all, on the basis that you are trying to obtain a constant temperature it may be good, so the fans start spinning slowly once the temperature goes past thermostat opening, and ramp up until full speed is attained at about 90 degrees, maybe a little less. It's probably quite a narrow operating range, maybe that's why you don't see it often.
Click to expand...

One thing I have some concerns over is how important is it to have an accurately regulated radiator temperature as after all the mechanical thermostat whilst an old technology solution is a very accurate and reliable one providing an analogue metering system that works at a first principle basis and in much the same way as PWM fan control regulates water flow in a progressive manner.

My veiw at the moment is that the electric fan will work as an adjunct to low vehicle speeds and idle conditions and for the majority of the time when driving will not be in use. The only precondition that the fan needs to adress is a suitable reservoiur of cooler than thermostat temp opening point water and that the radiator temp should be maybe 5 to 15 degress below that thermostat point to provide a thermal bank against fan cooling lag.

Knowing at what point in the system you need to monitor temperature is a little confusing , most people say that you should monitor at the top of the radiator (or thermostat housing ) and other suggest the bottom of the radiator, I havent quite nutted that one out yet as both systems have some pluses and minuses to them and depending on your design criteria if you want to look at the system holistics or to micro manage specific functions either will work.

I need to also work out yet if I want to blow air thru the core from the bumper side or draw it thru from the engine side of the radiator.

There is a lot yet to research and learn :(

Graeme
 
I agree that variable speed is probably overkill, can't say I've seen any modern cars doing it, so it's probably not necessary.

Push / Pull really depends on the fans you can source, I used a citroen BX fan on my 2200TC mounted in front of the rad to push air through, with the engine fan removed this gave loads of space between the engine and rad. I needed this as I was working on an engine management system for this engine and needed to mount a crank sensor on the front pulley. However most fan are mounted behind the radiator pulling through.
 
I recall discussing the fitment of a thermatic fan into my P6B with the service manager at the Range Rover centre that I frequent. If I recall correctly, he said that the thermatic fans in the P38 Range Rover (4.6 litre engine) actuate not only on temperature but also on coolant pressure.

The engine fan in my P6B is a 13 blade nylon arrangement that operates on a viscous coupling that limits fan speed to 2500 rpm. I would like to fit a thermatic fan too, but the available space is such that fitment is just not possible, given that I run both a transmission and an engine oil cooler, both of which reside in front of the radator.

The V8 Range Rovers from the 3.5 through to the 4.6 have always run three fans, the engine driven one plus two thermatic fans mounted in front of the radiator.

Ron.
 
First off, where to monitor temperature. For my money the answer is absolutely clear - as close as possible to the working area of the cylinder heads! Heat absorption into the engine occurs primarily at the containment surfaces for the combustion, ie cylinder head combustion chamber surface and the extreme tops of the cylinder bores. It is very important these don't melt! The nearest we can get to monitoring their temperatures directly is by looking at coolant temperature exiting the head as close to source as possible. As I noted earlier we further want to achieve as near constant a temperature here as possible so that it is possible to set up the carburation to give a consistent result. The temperature of water entering the bottom of the block really isn't very interesting in this context and will in any case vary according to how fast the coolant is circulating in order to give the desired fixed temperature output from the heads. The objective is NOT to run the radiator at a constant temperature, rather the cylinder heads!

So the practicalities of where to monitor? The S2 V8 can be fitted with a thermostat housing having a "spare" mounting for a second temperature sendor. This is the best easy solution. Next up is the hose adaptor mentioned by quattro. This is a short length of (normally) alloy tube of the same od as the internal id of the top hose and carrying a stub to mount the temperature sender into. The top hose has a section cut out of it and this adaptor inserted in place. Third from a temperature monitoring standpoint is the Kenlowe method of slipping a capilliary under the hose to radiator joint. Finally it is possible to get your radiator rebuilt with a standard modern car fan thermostat / switch incorporated into the hot side tank. Of these methods I personally would discount the Kenlowe method as being an engineering wise flawed method although I know many people get it to work OK. S1 V8's can't use the thermostat housing referred to so on mine I've actually gone for the rad mounted combined stat / switch on the basis that I'm prepared to make that level of compromise from the ideal and that it eliminates quite a lot of the circuitry (simple has a great deal to recommend it in engineering).

To pull or push? Well a puller fan is always desirable because then the radiator protects the fan motor to some degree from water, salt, debris etc entering the rad. But most madern fan motors are pretty robust these days so it isn't that crucial. There are no other performance implications, so just go with the most convenient mounting for the physical space available.

I really don't understand the idea of running both a mechanical fan and an electric. To my mind they are mutually exclusive. If you have correctly sized the radiator (UK territory V8 rads are NOT sized correctly!! - an additional core row is required for hot weather stationary traffic or a complete shift to an alloy rad) and corectly sized the electric fan, then the engine fan simply serves to lower the coolant temperature below the correct temperature you have chosen for your carburation set up! And it consumes unnecessary power and petrol! And that particularely includes the hydrastatic fan (Ron)! The very area you are seeking to most keenly manage is low output, low revs and low road speed where the hydrostatic is still working. At high outputs and high engine speeds the problem is much easier to manage. Similarely if you have an adequate mechanical fan design why would you want to add an electric one in tandem?

So don't forget the reasons for doing the job: 1 attain a much more consistent temperature at the cylinder head combustion face. 2 eliminate power and efficiency losses from the mechanical fan.

I would suggest that if you are comntemplating this mod as a solution to a lack of cooling then there are other things you need to address as well as the fan! ie fit a bigger radiator!

Chris
 
I would suggest that if you are comntemplating this mod as a solution to a lack of cooling then there are other things you need to address as well as the fan! ie fit a bigger radiator!
Click to expand...

I would suggest that one of the factors here is traffic levels, when the cars were designed you didn't spend long periods sat in stationary traffic !
Again this does lend itself to the electric fan, so you can get high levels of flow whilst stationary which simply aren't possible with the engine fan.
 
SydneyRoverP6B said:
The V8 Range Rovers from the 3.5 through to the 4.6 have always run three fans, the engine driven one plus two thermatic fans mounted in front of the radiator.

Ron.
Click to expand...

Don't forget that Range Rovers are very different animals prepared to perform in far more adverse conditions in comparison with our P6s.
Just imagine having to crawl in low range pulling a few tonnes up a hill in 40+ degrees C. You will need a gale to keep that V8 cool!
 
keanej said:
I am interested in these as the switch is set into a tube which fits in your top hose (the top hose is cut and the stainless tube jubilee clipped into it) unlike the stupid kenlowe way which is almost impossible to seal.

Not adjustable though?
Click to expand...

There is an adjustable type available see demon tweaks
Click to expand...

So there is - ta very much :)

http://www.demon-tweeks.co.uk/products/ ... e=GLORREFC

perfect addition to an existing or aftermarket electric cooling fan. This innovative, highly accurate controller is available in a number of installation options all offering simple and efficient control of cooling requirements. In-line - simply split the coolant hose and isert the aluminium adaptor. Activation termperature can be adjusted to between 70 and 120°C.

Available to suit 25, 28, 32, 35, 38 or 45mm ID hose.
Click to expand...
 
webmaster said:
I would suggest that one of the factors here is traffic levels, when the cars were designed you didn't spend long periods sat in stationary traffic !
Click to expand...
I think that's a bit of a myth isn't it? Although the amount of cars on the road has gone up there were still plenty of traffic jams in the 60's & 70's as the road system wasn't up to the standard it is today as regards to bypasses/motorways..etc.
 
I think with the P6b overheat problems are really a symptom not of overheating but a symptom caused by modern fuels and there abilitiey to vapourize at lower engine temperatures.

Graeme
 
The function of the radiator is to get rid of the heat that has been liberated from your petrol and hasn't been converted to motion! A rule of thumb for mechanical conversion systoms would be an efficiency of 33%. ie 66% of the energy of the petrol needs to be got rid of as heat. Our P6's could well be down nearer 20% with 80% to lose through the rad.

The key to understanding this discussion is to realise that any change in efficiency of the engine is doubled in the effect on the radiator! Thus a small improvement in engine efficiency has a large effect on the cooling requirement.

Equally a small decline in engine efficiency has a doubled effect on increasing the requirement for cooling in the radiator. If you look at the history of the P6B there are a number of changes which have reduced the efficiency and performance of the engine. Not least lowering of the CR from 10.5:1 down to 9.25:1; retarding the ignition to cope with lower octane fuels; and yes, poorer quality modern unleaded fuels.

So the size of radiator originally chosen by Rover for the early P6B and unchanged throughout production, is much less adequate today than it was in '68 irrespective of any deterioration in the caondition of the system.

If you want to claw some of this deterioration back, first off return the engine to it's original settings and use fuel additives to replaicate original fuel qualities. Then make sure that the carbs are in tip top condition (see other notes on balancing dashpot fall times etc etc) and correctly set, that the ignition system is A1 and preferably convert to electronic. You can also make some wins in the cooling system by eliminating the engine driven fan (!!!). Every horsepower used to drive that fan generates two to be dissipated through the radiator!! If you can use less power by switching to electric fans (which you can by a significant margin) then you start a virtuous circle. Less is more in this context! Then a free flow exhaust and extractor manifolds will not only liberate more power from your engine for overtaking etc, but also reduce the cooling requirement under the same conditions of usage! Similarely gas flowing cylinder head and inlet manifold gas tracts. But note that if you start messing with the cam or increasing capacity you don't necessarily improve efficiency!

Chris
 
Hmmm spot the engineers lol :LOL: all absolutly true and yes this has been the focus on my P6B to elliminate the factory inefficiencies that were built in. Not sure that I would want to change the compression ratio to the origional 10.5 to 1 as that would cause more headaches than pleasure, have already replaced origional carbs for the Weber 500, cooling fan will be next then if cash and inclination allows the timing gears though they were changed in 1989 but I dont know if factory or aftermarket were fitted as I wasnt to concerned at the time as I did not know of the there dubious design.
I myself am an Electrical engineer. I presume you are of a similar persuasion.


Graeme
 
I can certainly agree that the dual core radiator in its orignial design is totally inadequate, especially in hotter parts of the world such as here in Australia. To that end I have been running a three core radiator for some years now, and it certainly makes a positive difference.

Graeme,...I don't necessarily agree that the vapourisation point of modern fuel is the dominant factor in overheating problems with the P6B. Certainly my original 10.5 : 1 CR engine was much harder to keep cool on hot days in Sydney traffic compared to the 4.6 (8.37 : 1 CR) I now run. In both cases the thermostat employed is a 74 degree C item. The bigger engine is just so much more efficient.

Going back to 1985 when I started driving my Rover, pinging and hot running in traffic was always a problem. Timing was retarded to TDC to satisfy the fuel requirements but of course such an inefficient ignition setting just added to the overheating problems. Essentially a no win situation. In reality I think, the compression ratio was just too high for the engine design and the ignition system employed. The P6B owners that I know whose engines are of the 9.25 : 1 CR derivation never have the overheating sensitivity that plagues the higher compression models.

Ron.
 
SydneyRoverP6B said:
I can certainly agree that the dual core radiator in its orignial design is totally inadequate, especially in hotter parts of the world such as here in Australia. To that end I have been running a three core radiator for some years now, and it certainly makes a positive difference.

Graeme,...I don't necessarily agree that the vapourisation point of modern fuel is the dominant factor in overheating problems with the P6B. Certainly my original 10.5 : 1 CR engine was much harder to keep cool on hot days in Sydney traffic compared to the 4.6 (8.37 : 1 CR) I now run. In both cases the thermostat employed is a 74 degree C item. The bigger engine is just so much more efficient.

Going back to 1985 when I started driving my Rover, pinging and hot running in traffic was always a problem. Timing was retarded to TDC to satisfy the fuel requirements but of course such an inefficient ignition setting just added to the overheating problems. Essentially a no win situation. In reality I think, the compression ratio was just too high for the engine design and the ignition system employed. The P6B owners that I know whose engines are of the 9.25 : 1 CR derivation never have the overheating sensitivity that plagues the higher compression models.

Ron.
Click to expand...

I only started experiencing problems with mine when NZ went to unleaded fuel which was one of the reasons for my carb change, however when I changed the carb I ended up with vapourisation in the carb which on Saturday I cured (fingers crossed) with an Edlebrock heat insulating kit. 9.25:1 witha V8 engine seems fine to me higher compression makes things a little on the edge when it comes to getting the tuning correct.

Graeme
 
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