robski

Some good stuff going on in the number 3 bigend thread, so I didnt want to start this one there.

Question : why do we have both oil and water doing a cooling job in the engine.
Obviously oil is there primarily to keep metal parts apart, and provides the cooling as an extra.

However, Im interested in what proportion of cooling the oil is supposed to provide? Is it SUPPOSED to provide any?

Also, does the water jacket provide enough cooling in its own right to keep the engine within operating parameters? (i.e. assuming the oil doesnt do any cooling, but keeps components well lubed)

Does the scoob have an "oil to water" or an "oil to air" oil cooler?

Why? Well I was wondering whether it would be worth running the engine a tad cooler by using a slightly lower temp ranged thermostat. Or is it the case that the cooling system would be open all the time anyway when running at reasonable speeds?

I am assuming that the ability of water to remove the heat from the engine would be sufficient, and that this would allow the oil to better do its primary job of providing the lubrication rather than helping with the cooling.

Ready to be shot down in flames

robski

chiark

The scoob has a doughnut oil to water heat exchanger which has the effect of warming your oil quicker when cold, and taking away heat from the oil when up to operating temperature.

It takes a hell of a long while for oil to get up to temperature (like 10 mins minimum)

I don't think, but likewise have flame suit on, that oil provides great cooling.

Adam M

Oil must provide some cooling otherwise they aouldnt have oil squirters which directly cool the piston from underneath.

Water is used to cool the block down, but it doesn't actually directly cool the pistons, which must surely get hotter than any other part of the engine as they do not have substancial mass to conduct and radiate the heat away and are not in contact with cooling water in the same way as teh block is, therefore I can only assume that any cooling they receive is through direct contact with oil.

Obviously the lubrication properties of the oil are most important too.

Sam Elassar

i thought oil stopped the oil squirters since MY95-96 so it couldn't have been a good idea.?

sam

MorayMackenzie

robski,

Oil does contribute to engine cooling... it's part of it's function. It also has to absorb and hold byproducts of the combustion process, which is mostly why it goes black and requires regular replacement, mostly.

Adam,

Not all engines have oil-squirters under the pistons.

Moray

*********

moved to drivetrain

John H

The doughnut oil cooler imho seems to offer the best of both worlds as it heats up the oil when the engines cold and cools the oil when the engines hot.I know there's aftermarket oil cooler kits (oil to air) out there but would is it possible to fit an up-rated doughnut oil cooler ?
Are they available? (maybe fron STi variants)
Perhaps its possible to modify the std. doughnut oil filters so they can be sandwiched together doubling the heat transfer ?
Or maybe an oil to air oil cooler kit fitted with an oil thermostat is better again? I realise it also increases the capacity of the oil system so reduces the rate at which the oil breaks down, increases acidity etc..)

Can anyone advise me ?

Regards,
John

Bob Rawle

Oil definately cools, any liquid moving over hot surfaces will remove heat given that it is moving, oil cooler is specifically designed to speed up oil warming process, the quicker a turbo gets hot oil the better the bearings like it, no turbo should be boosted when cold, 10 mins (5-8 miles) warm up time is about what mine takes, 80 deg minimum before boosting is wise.

Piston relative temperature is far greater than the oil so the cooling effect would be significant, the dpownside is that the oil will run hotter as , in turn, it becomes more heated.

I believe that an oil cooler is an advantage as long as it is thermostatically controled and the thermostat does not allow the dumping of colder oil into the system all at once when it opens, so a stat set at 90 degrees opening and 85 degrees closing would be pretty good, an oil cooler also has the benefit of increasing oil capacity as jon=hn mentioned. The downside is that when you do an oil change then its not easy to get the oil out of it and it does need changing along with the rest, those with coolers and who don't take this precaution would be advised to take care.

Be careful running the engine with a cooler thermostat on the standard ecu, the ecu uses coolant temp to help it determine fueling, if coolant is too cool it will not realise that the engine is "warmed up" and will be adding fuel as if it was still cool. Not good as the fuel settings are then "out" under all conditions (too rich).

JIM THEO

Adam M

"Obviously the lubrication properties of the oil are most important too". What properties you mean?

I used to have Aral 5-50 (not famous except in Germany) full synthetic. What all of you think about the correct viscosity for the scooby?

WREXY

Hi Jim Theo,

For the Greek climate I have been told by an engine specialist 10/60, preferably the castrol RS

WREXY.

Jan Shim

It takes more than 10 minutes of idling to get oil temps to 60ºC mark which is what i do every morning before driving off to the office (one of the added benefit of a turbo timer). It takes another 5 minutes of easy driving to bump it up another 10º-15ºC (plus the cold air keeps the oil temps reasonable low so you wont be seeing 80ºC so quickly).

The ecu uses the temp sensor to determine how much fuel to enrich during cold starts and the lower the temperature, the higher the increment rate. Fuel enrichment stops when temps have stabilised at 60ºC.

Bob, what does this mean if you fit a thermostat that's rated 68ºC (eg ARC thermostat) will the 8ºC window cause any overfuelling issues ? The factory thermostat is rated 78ºC I think ??

robski

Question for Bob Rawle :

if running a cooler thermostat could fool the standard ECU, would this be ok with for example the link?

Also, do you personally think that running the engine slightly cooler would help lower the temp of the oil? Or is the current oil temp close to the ideal anyway?

robski