THOMO

why is it that dealerships are putting in 10/30 fully synthetic oil in these performance cars ?

it would appear that performance garages preffere to use 10/60 10/50 fs.
ive always used 10/50 or 10/60 and not had a problem.

is there anyone changed from 10/60 to 10/30 fs and noticed a change in the cars drive ?

oilman

iTrader: (9)

It's because the correct grade for a stock car used on the road is sae 30 or 40 and not sae 60.

The main reason for stepping up to an sae 50 or 60 would be oil temperatures.

Above 120degC an sae 50 is adviseable as it will only thin to the equivalent of an sae 40 at 100degC.

I personally don't recommend an sae 60 as it's too thick IMHO.

Here's a chart which explains what I mean.

Modern high performance engines are designed to run on an oil viscosity of 10 to 15 cSt. (But many are OK on less than 10.) 30cSt is too high at high RPM. It can lead to foaming, air entrainment and cavitation.

............Temp. for 30cSt (Deg. C).......Temp. for 15cSt.......Temp. for 10cSt

5W/40..................71...........................9 0........................117...............
10W/40................70...........................99. .......................118...............
10W/50................80...........................109 .......................130..............
10W/60................89...........................119 .......................142..............

This shows that a 5W/40 or a 10W/40 is perfectly adequate for all engines except those that run an unusually high temperatures.

Also, a thick oil can lead to trouble unless properly warmed up before high RPM is used.

Cheers
Simon

THOMO

simon thanks for the information .
one more question. what temperature should an evo and scoob be running when driven hard ?

Bob Rawle

Depends on the oil, seriously I have recorded a 10 degree difference in temps between a 5-40 and a 15-50 grade. Significant

bob

THOMO

so what grade would you recommend bob ?
pm if its top secret bob

Brun

If it's top secret he ain't gonna pm it either

oilman

iTrader: (9)

I would have said generally between 90 and 100degC although I have heard of up to 120degC in some modded ones. It depends on the mods and efficiency of the oil cooler.

One of the problems with running a thick oil in a car where the oil is cooled to 70-80degC is the possibility of air entrainment at high revs which can cause engine failure.

In general the best advice is to use a thinner oil if oil temps are low as it flows better eliminating the bearings being fed slugs of air.

My chart above illustrates this well.

I would always not go thick unless you have a sound technical reason for doing so.

Cheers
Simon

oilman

iTrader: (9)

I agree, it is significant but the reasons for this are that thin oils dissapate heat better and therefore the oil may be hotter in the sump but the engine internals are in fact cooler because of this.

Cheers
Simon

ALi-B

iTrader: (1)

Agree, thicker oils aren't always better. Even though they withstand higher temps better, they can actually cause higher temps in the first place. There also the point they decrease the MPG for those who are bothered

One of reasons why Subaru along with many other manufacturers recommend thinner oils nowadays, is partially down to the modern oils used can stay within their rated grades and viscosity for a longer time than previous (even semi synthetics). This is partially why Subarus have lengthened their service intervals from 6month/7.5K to 12month/10K on their newer cars as the oil is capable of withstanding longer drain periods.

With older/cheaper oils there is always that risk that the oil will degrade and lose its rated properties before it is due for changing. Thus the old addage in oil decisions: Use cheap mineral oil and change it often or use use expensive synthetics and change it less often. Most Japanease manufacturers use the previous idea and principals and have shoter drain periods. But the German manufacturers prefer to use the latter principals and use longer drain periods.

THOMO

what are the manufacturers recommending ?
im pursuming they would of done various tests to keep the engine cool at the highest temperatures

oilman

iTrader: (9)

On later cars, the stock (on the road) recommendation is 5w-30 or 5w-40.

It's the 30 or 40 that indicates the high temperature requirements.

Cheers
Simon