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MG Midget and Sprite Technical - Here's one for all you thermal dynamicist

I was sitting in traffic and while the temperature wasn't going higher than it should, I wondered what was a more effective cooling solution.
Assuming a normal cooling system, either crossflow or downflow with a later fanblade.

1.Sitting with the engine at tickover (fan going round relatively slowly, water pump also not at max)?

2, Slightly higher revs (engine producing more heat but blade running faster and water pump pumping water faster)?

3. High revs (engine producing far more heat but blade running much faster and water pump pumping water much faster)?

Just wondered.
G Lazarus

With a system in good condition then i would say option 1 as the engine will produce the least heat energy just idling, and the fan/pump should have been designed to keep everything at a level temperature at those revs.

However i suspect that number 2 is the more likely with an older engine...

I had the this issue with a mini. If i was stuck in traffic during the summer and not using the heater then the temp would creep up. But if i held the revs at 1000 then it would come down again and be steady.

Does anyone use the thermostatic mechanical fans ? not sure how they work but they are fitted to a lot of pickups nowadays. I understand that they let the fan slip when engine is cool and lock up to turn the fan when hot...?
Andy Phillips (frankenfrog)

I don't know the answer, but...
it is well known that at anything above around 25 to 30 miles an hour the fan has little effect and perfectly adequate cooling is achieved by the ram effect through the radiator. So I suspect that the pitch of the fan blades would have been designed to be most effective at lower speeds which is when it is most needed. Of course that is road speed, not necessarily the same as engine speeds but the logic would suggest that tick-over is the best for cooling as regards the air fan efficiency.
Guy Weller

As Guy states, a cooling fan is only required at idle. If designed correctly, then I would suggest if you are stationary and the engine is operating at significantly higher revs than idle, you would eventually generate more heat than the fan on its own is able to cope with.

The increased flow due to increase in water pump rotational speed would make no difference in a closed system - to improve matters you would have to increase the efficiency of heat removal. To an extent, that is achieved by the increased rotational speed of the fan, but the efficiency of the fan drops off at higher speeds - due to friction losses, drag at the fan tips etc etc. Therefore, I would imagine that at stationary and as revs rise, the temperature would also rise until the point where equilibrium is reached - which I guess is fine, provided it does not begin to degrade the oil and start damaging the engine.

Personally, preservation of the engine would therefore prevent me from revving it at idle.


Alterntively of course, install an electric fan which only energises on demand! Far more energy efficient and far better as regards cooling efficiency - as it runs at only one speed and fan blade design is thus optimised for that speed.


Mark O

Biggest problem is when the pump starts pumping at a reasonable rate, Minis were always rubbish till about 1500 rpm when you could get a small amount of warm water in the heater matrix, below 1500 and it was ppor. On the rolling road I get the best cooling in terms of time taken to get to a 'normal' temp by letting the engine idle with my rolling road leccy fan blowing into the rad, then raise idle above 1500 rpm and watch the temp gauge plummet rapidly. Race Bs using the later rubber bumper larger water pulley matched with chrome bumper crank pulley runs slower (helps prevent cavitation at high race rpms) needs higher revs to make the water pump work in the first place.

Id go leccy fan and bring revs up if the gauge doesnt seem to drop fast enough in traffic to get the water round the hot part of the back of the block.

Peter
Peter Burgess Tuning

Yeah
Our Elan has an electric fan which works fine but if stuck in the traffic for a while the temp creaps up. I just give it a little blip on the throttle to circulate the coolant and it'll be ok for probably 5 mins till it starts to creap up again
Elans have very small crank pulleys making the w'pump too slow at idle -- willy
William Revit

Many thanks for the feedback.
As I mentioned, I don't have a problem with overheating, even in the most extreme situations (queuing at Le Mans in very high temperatures etc) I may have to put on the heater fan. In my case, the large panel gaps may help with heat extraction. However, the traffic jams that we experience in London(for example) are probably more extreme than the road conditions when the cooling systems were originally designed.
G Lazarus

in my experience of engine driven fans in my two Spridgets I'd definitely say 2, Slightly higher revs (engine producing more heat but blade running faster and water pump pumping water faster)?

not massively higher than normal idle but definitely more

easy to tell just look at the gauge, see whether 1,2 or 3 holds the needle from rising or helps it to drop back faster
Nigel Atkins

Hmmm... but you don't half look and sound daft sat in a traffic jam with your engine blaring away at 1500+ rpm! :-D

Malc.
M Le Chevalier

it depends on how hot it is outside, if its early spring or late fall...temp around 60F, then #1 is fine

For late spring to early fall then definatly #2

Im not a fan of #3 simple because of cavitation of both the water and the oil and the fluids move to fast to conduct any heat transfer....if anything it might be good for harsh winter with temps at minus -20F, not that id care to try that experiment

Prop
Prop and the Blackhole Midget

Malc,
I'd count 1,500 revs as being in item 3 not 2
Nigel Atkins

My IS60 gas turbine idles at 18000 and peaks at 46000 :) so 1500 seems very reasonable.

Peter
Peter Burgess Tuning

Peter...haha

Gas turbine ???

Yea know the NSA listens to us....do we even want to ask why you have a gas turbine...

Leaf blower?, hair dryer? Wifi rocket powered skate board ? Or because indiana jones rode a turbine engine in the last movie the Crystal skull


Hahaha

Peter you have the best toys a man could want.

Prop
Prop and the Blackhole Midget

All part of 'The Man Cave' :)

The gas turbine is a fire pump unit from an aircraft carrier, they used to use coventry climax engines but even with 9thou piston to bore clearance they were prone to seizing up as they had to work instantly and not have five minutes warm up! The rover gas turbine came into use instead, to the great delight of some operators who sent them off the flight deck into the sea on full power to see what would happen.

Peter

Peter Burgess Tuning

I believe the bottle-neck in the transfer of heat in the radiator is the air side rather than the water side, since the heat transfer coefficient for water is about ten times better than that for air.This is why the water pump is a primitive paddle type as that is all that is needed to just keep the water circulating.*
So doubling the water pump speed with a constant fan speed won't produce anything like the cooling effect of doubling the fan speed with constant pump speed.
Does that help at all? - probably not! I'll get my coat.

*I'm assuming here that the tube-side velocity is such as to bring the Reynolds number over 1600 thus creating a turbulent flow regime!
M J Chapman

At lower RPM it may be that the pump dosent have enough energy to pump the water around, it may be that it just churns the water in the pump body.
Adding a few more revs could just tip it over to get the water moving.

When i worked at a pump factory the rotational speed was never taken below 900 rpm, and that was with closed type impellers rather than the open ones in cars.

Of course as cooling passages get blocked with silt etc as the engine gets older the energy required to pump the same amount of water will rise, meaning more revs required to keep the engine cool at standstill.

I like the idea of the electric water pumps, then you can vary the flow according to the water temperature rather than as a function of engine revs.
Water gets hot, you increase the flow rate, water is cool then decrease the flowrate, engine revs shouldnt have anything to do with it.
Also you can set them to run for a few minutes after engine is switched off to cool the engine down evenly.
Andy Phillips (frankenfrog)

I am with Andy, I think electric water pumps are the way to go. Mechanical pumps have so many compromises. Water flow should be a function of the rate heat needs to be removed from the engine. When cold the water flow does not need to be particularly fast. Climbing a hill with a full car at low revs will need more flow to keep things cool.
I am waiting for an electric pump kit to fit the midget with all the pipe work and blanking plates etc. included and an ecu that will control both water pump and fan.

Dave
Dave Brown

Dave,

Its available, but pricey....


http://www.carbuildersolutions.com/uk/electric-water-pump-115-lmin-and-controller-kit

Andy
Andy Phillips (frankenfrog)

If everything is in good condition then No1. The fans themselves do not necessarily work better the faster they go and their designed (or not) aerodynamics probably give them a narrow effective speed range, above which they are likely to shear rather than push the air-mass.
Nick Nakorn

Also here: http://www.jjcraceandrally.com/race/electric-water-pumps

Still quite pricey for the full kit with a controller though.

It looks as though the controllers will also manage electric fans.
Colin Mee

Peter, rover gas turbine man portable pumps, engineers nightmare, have spent many a sunny Sunday morning trying to get the bloody things to run before retiring to the bar for a few pints of cab and a curry.
d brenchley

We have been ok once we read the instructions, 2 1/2 turns of the crank, throw the fuel switch and , fingers crosses off you go and slowly increase cranking. Originally we were told we needed as fast as possible then throw fuel switch.....this only seemed to result in a big 6-8ft flame from the exhaust! Exciting in the dark but not good!

Youtube link, my mate Matt Smith firing his is60 up the wrong way!!!

Put the sound vol up....Matt is ex army :)

https://www.youtube.com/watch?v=zJCtc34JPuQ

Peter
Peter Burgess Tuning

P6 is No2. It even says in the book, if setting up things or idling it says that you should blip the throttle every so often to stop it overheating (and the oil pump is rubbish so it helps there too)
Rob Armstrong

Hi gentlemen,

Theory is nice. I am in the possession of an ebola thermometer. I measured the temperature on several points and RPM. Upper side radiator, under side radiator , exhaust and inlet. Steady state after 5 min, readings in degrees Celsius. Open is with hood open. The correlation between gauche and radiator upper side is poor as it is not easy to read the gauche properly. I guess the range of the ebola meter is 2-3 degrees in lower temperatures and 8-10 in higher as the measurements fluctuated.
Witch of your theories are true?




Flip Brühl

ebola meter


Flip Brühl

I love my ebola meter also, but its very archaotic.

On mine I cant aim it at anything electronic otherwise it can become damaged....im not sure why?

Prop
Prop and the Blackhole Midget

Peters you tube link with out the "s"

Prop


http://www.youtube.com/watch?v=zJCtc34JPuQ
Prop and the Blackhole Midget

Peter,

That would make an awsome BBQ grill

The Flame on Grill...

Any chance you can do a youtube vid of the (flame on grill) BBQing a chicken as a late night infomercial... like " ronco ron " used to make with spray on hair, chia pet, and ginsu kitchen knives

That would be classical epic

Prop
Prop and the Blackhole Midget

My conclusions so far:

City driving and 3000 RPM at stand still produce more heath than idle (800 RPM) . Cooling is more efficient at 3000 RPM ( difference between upper and underside radiator) but can not overcome the excess of heath produced ( upper side radiator temp and exhaust). Pump is working better at 3000 RPM. Closing the hood lowers the temperature on in and outlet!
I use a plastic fan. A deep impeller water pump, A upgraded radiator (tree cores) and 50 % water/glycol. I bought the ebola meter before the hype about ebola . It costed me only US$16 in Hong Kong and it is not archaotic.


Flip Brühl

This thread was discussed between 14/10/2014 and 18/10/2014

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