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MG MGF Technical - Stupid cooling question

I know these assumptions are not quite true, but within 5%?

If the engine creates a constant amount of heat &
the airflow thru the engine bay is minimal &
the water is the only thing cooling the engine

therefore
the heat of the oil will settle at the pint where it gets heat from the engine and conduts the same amount of heat into the water

so why would a water/oil cooler be more of a problem if the water system was not up to scratch?
Will Munns

Will
I think I made a similar point earlier; I see no problem for the oil->water cooler, esp. in Britain.

Can somone ( I think Rob made the point initially ) explain why the cooling system is not up to scratch ?
Set up correctly it appears to have plenty of capacity - even for extended track use; mine has done 15-20 consecutive hard laps around Castle Combe without problem (oil got very hot though!).

I think I'm going to have to get an oil->water cooler just to test the theory !

Steve
Steve

Will,

I think the oil runs a lot hotter than the water so in you theoritical scenario the water will overheat before the point of settlement.

I think Roger mentioned that the new TF160 is fitted with an oil/water cooler.

Spyros
Spyros Papageorghiou

Yes, but once the oil reaches tempture the excess heat has to go somewhere - so into the water it goes. If the oil temp was alowed to get to 130 and then dumped into the water I could see this problem, but with a water/oil cooler this doesn't happen- simply the heat is vented long before the oil reaches these high temptures, thus as a constant amount of heat is generated, the water won't get boiled.

Or am I missing some subtle point?

Will
Will Munns

I know most owners of MGF VVC abingdon trophy cars competiting in the races ended up going for a oil cooler as the oil temperature did get quite hot while pushing the car lap after lap.

1.8i did not seem to be so effect by oil temperature.

The only MGF to come out the factory with a oil cooler I belive was the steptronic. I could be wrong though.

Tom
Tom Randell

Tom,

I think the steptronic has an oil cooler for the gearbox fluid but not the engine oil - but I could be wrong as well.

Spyros
Spyros Papageorghiou

Guys, I agree with your premise: the majority of the heat in the oil is actually going to be taken up ny the engine's cooling jacket rather than through radiation of heat into the engine bay.

I also agree that the capacity of the cooling system is more than adequate to cope with the 'increased' heat load of an water/oil cooler.

So why the concern? Remember that old chestnut of temperature cycling, and the temperature gradient across the head and block as a cause of head gasket failure? It may be possible (I do not know) that an water/oil cooler just might exaggerate this - and might be the possibility why MG Motorsport and Racing have decided upon the air/oil coolers for MGF Cup cars. But that's speculation on my part. All I do know is that those who have gone down the route of water/oil coolers have also fitted remote thermostats (Simon Scutham for example) which in practice has eliminated the HGF issue, and effectively 'clamps' the water (and therefore the oil temperature) to 80C. No more oil degradation (oil stays oil colour as opposed to nasty black treacle which is usual MGF/Elise fare).

As fitting a remote thermostat actually is not all that difficult and the parts are cheap, I reckon that it makes absolute sense to modify the cooling system in this way at the same time as installing an oil cooler.

Hope this makes some kind of logical sense?
Rob Bell

May be a strange question Rob, but where does a remote thermostat go? and why were Fs not equipped with them to start with?
Kingsley

Kingsley, have a look at dieters site- then look for Carl- all will be revelaled
Will Munns

Ar*e, I can't find it!
Essentailly the cooling circuit is a tight loop that consists of tracks thru the head, a water pump and some short external pipes with two sensors in them (for the gauge and MEMS). Also attached to this circuit is a longer circuit which runs thru the radiator, this circuit is shut off by a thermostat (88 deg?).
So what happens is the engine sits there cold until you start it
then the engine and the short track come up to tempture quickly
then the thermostat begins to open (this should happen slowly, but the K warms up quite fast)
then water is pushed around the larger circuit as well,
----note this water is cold ~15deg and the engine water is ~90deg
the head cools rapidly causing the thermostat to clamp shut and the procedure is repeated
this will continue until the coolent circuit is up to temp when the fan will do some of the work
If you are driving then the circuit may never reach temp and the engine will continue temp cycling

to put in a remote thermostat you change the closed coolant circuit so it includes the underbody pipes and only the radiator is bypassed, in this way the fluctuations are not so severe

Carl? has gone one step further using a 82deg thermostat at the engine - giving fast warmup times, then a 88deg thermostst at the radiator, giving less fluctations in the engine.

Will
Will Munns

An Australian Co. (Davies Craig) makes an electric water pump (and a controller) which could boost the mechanical pump at idle, or pump coolant after ignition off. It's in demon tweeks catalogue.

Steve
Steve

http://www.users.globalnet.co.uk/~scuffham/Water%20System%20Mods.htm
gives an example of a remote thermostat on a lotus - for MGF just forget about the warm cills when reading

Will
Will Munns

Will, Kingsley, the direct link to the page on Dieter's web site that deals with this question is http://www.lame-delegation.de/mgf-net.de/thermostat/Water_System_Mods.htm

It also has details of Carl's version of Simon's modification for the MGF.
Rob Bell


Hi all,

after the initial runs with this dual thermostat system and a temp. data logger borrowed from my work I must say that the coolant system is now rock steady !See separate thread some time ago.
So all logger temp senders were removed after a week and the system has been in use for several months now - both normal leisure driving as well as on trackdays and other events. IMO well worth to do on any MGF outside warranty with or without the new headgasket and steel dowels. My -97 VVC is on the original gasket and it will be interesting to note if I get any prolonged time of driving before the HGF hits me ! The remote thermostat used by me might be a bit hard to find in UK but You have more access to the look-alike Rover SDI type that will fit equally well. The T - piece may be the biggest stumble. Time for a DIY-kit Mike ?


Regards , Carl.
Carl

Carl,
How long before thge heater warms up?
Have you considered fitting an oil to water cooler?

Will
Will Munns

<<Time for a DIY-kit Mike ?>>

with the number of people worried (paranoid) about HGF, and temprature problems, its sounds like a good seller.

paul weatherill

Carl, I wonder whether the drilling of the existing thermostat is strictly necessary?

I'll certainly be looking into performing this mod in due course :o)
Rob Bell


I have not noted any prolonged wait for the heater matrix to deliver hot air, might just be a tiny bit longer. Remember that the holed "original" thermostat lets thru only small amounts of water and there is no passage thru the front cooler until the water is up to temperature. So really not that big diff. under warmup. The change is really for a more stable servo system in the total loop !
I am one of the lucky ones that during no events have recorded abnormal oil temps.Let it be 20 min trackstints or motorway driving on a hot day. Never goes above 120 deg. C measured witha reliable temp sensor. Just wonder how much leeway there is in the original measurement system ? A slightly dodgy temp. sender and a not so well calibrated mechanical readout can give quite a diff. from actual temperature!

So for me there is no immediate plans for any oil-cooler. And if I ever change my mind I think I go for the Laminova oil/water type.

BR, Carl.
Carl


Hi Rob,

well, to be honest I only drilled the "original" 82 deg. C thermostat because I dont like that path to be totally shut ! I can now shut the heater matrix instead and still have some cirkulation in the engine block. Remember on almost any other thermostat there is a small "jiggle valve" that althou small lets water and trapped air thru and also eases fillup of new coolant and bleeder procedure... A 3 mm hole will do nicely, any bigger might prolonge warmup time too much in wintertime.

BR, Carl.
Carl

Ok, I think I read it wrong, the original thermostat is still there, but has a hole in it?
if so is it still rated at 88Deg?
How big is the hole?

Will
Will Munns

I believe Carl's conversion uses a 82C thermostat with a single 2 or 3 mm hole dilled in the mounting ring, Will. I don't see any reason why a 'normal' standard 88C thermostat would not work in its place - and in fact, the drilled hole may not be necessary, although it'll reduce the temp fluctuation in the '3rd' circuit.

To summarise Carl's conversion, the cooling system now consists of three circuits, from the OE two:

Circuit 1: circulation around the engine block (thermostat closed, and water circulates only in the engine and hence rapid warm up time in the standard engine as the water volume is small).

Circuit 2: radiator circuit. The volume of this circuit is much larger - and predictably much much cooler - than the engine circuit, wherein the problem lies - when the thermostat opens, there is a big volume of cold water that suddenly drops the temp in the cylinder head - whereas the block remains warm = differential expansion/ contraction.

Carl's mod adds a third, intermediate circuit -

Circuit 3: a thermostatically guarded water circuit warmed by a constant 'trickle' of water through the standard thermostat, but obviously cooler than the engine circuit due to heat radiation from the pipe work. Larger volume of water than the engine circuit (it is basically circuit 2, sans radiator), but warmer than circuit 2 (because heat loss is less efficient than via radiator) - so less of a thermal change at the cylinder head and thermostat when thermostat opens. When the water in circuit 3 gets to 80C or so, it opens into circuit 2 - so effectively the cooling circuit is now operating as OEM.

Basically it should, and evidently does, result in a more stable closed circuit control system.
Rob Bell

Will, if you haven't already, check out the F-TF modifications thread. Mike's discovered that the oil cooler in the TF is of a water/oil heat exchange type...

I'm surprised given previous experience of MG OEM specification, but lends credance to what we propose :o)
Rob Bell

Gentlemen,

Maybe this is a stupid question, but wouldn't the simple move of opening the heater circuit (i.e. turning up the heat to maximum together with the fan) a few minutes before switching the engine off, and leaving the heater in that position for the next cold start, in effect amount to the same as Carl's circuit 3? The turning up of the heat before switching off should help lessen the heat sink problem of a switched off hot engine and the open heater circuit should provide some gentle cooling of the engine during a somewhat longer and more progressive warm up period.

Or am I talking complete nonsense? :-/

Per
Per

Not talking nonsense Per - but what Carl's modification achieves is different to the opening of the heater circuit, and more beneficial to the normal running of the engine.

The reason is that Carl's circuit heats the water in the underbody coolant pipes - that are normally cold.

When the radiator circuit opens, the coolant return temperature is warmer - because the cold radiator coolant is mixed with the warm water already in the pipes (and remember that thermostats open and shut reasonably slowly). Therefore the coolant being returned to the engine is less cold and therefore less of a thermal shock to a hot engine.

That's my understanding of how things work - Carl, Dieter, would you guys agree with this?
Rob Bell

This thread was discussed between 13/06/2002 and 18/06/2002

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