5x40 versus 10x50 oil

[Juddder]

Not trying to start a big debate here , but reading previous posts there seem to be strong recommendations for both of these types of oil (both fully synthetic).

As my engine has been rebuilt twice (8,000 and 28,000) and is now relatively high mileage (40,000+) I am thinking that the slightly thicker 15x50 would be better for it, as it doesn't need any posibility of metal/metal that the thinner oil could give.

However there is some debate that you lose power with the 'thicker' oils.

Anyone a bit of an oil/cerb guru able to advise which way to jump?

Edited by Juddder on Tuesday 25th August 18:28

[jammy_basturd]

Any power loss would be unnoticeable (sp?) unless you were hitting consisten lap times around a circuit.

Thicker oil is in practise just masking wear issues. May or may not be a problem for another several thousand miles though.

[stuthemong]

I recently had a service at APM. Andy uses Mobil 1 15w-50 fully synth and I'm not going to argue with the man who built my engine!

As luck would have it, Halfords have it on special at the moment, ( http://www.halfords.com/webapp/wcs/stores/servlet/... ) - I'll just buy a 5L which will do me for a long while to come - can't argue at that price (was about to buy from Opie, but that's £12 dearer due to the offer)

Stu

[350Matt]

Al melling ( the designer of the engine) was asked this at the middle wallop talk

He said to use a 50 weight oil 15-50W or 0-50W

[ridds]

With a 50 weight you will loose a certain amount of power, however if you drive your car hard it would be beneficial to use.

If it's just motorways and a roads you use then a 40 is fine, particularly with the amount that the Cerb over cools its oil.

One of the quick and easy ways to free up more power out of an engine is by reducing friction, dropping a grade on oil is an easy way of doing this. IF the bearings can survive that is.

[jammy_basturd]

I doubt the power lost would be more than a few ponies, probably less than what you lose by driving the AC pump. If your that intent on gaining every last bit of hp then I'd start with slipping off the AC belt and trying that.

[ridds]

A/C idler, when not engaged will use about 0.5-1hp. You can loose up to 5-10hp with a thicker oil grade.

PAS systems can absorb a similar amount, up to 15hp, hence why I've kept my electric setup at them moment

Dyno research on various road and motorsport applications.

[Juddder]

Spoke with Guy at Opie Oils (via email) and he recommended 5w-40

"I would go ester based synthetic as these are elctrostatically charged so they will cling to the metal, leaving in the bores etc a protective layer of oil, this is ideal for next startup as there will already be oil in the banks. 5w-40 is the grade to go.

Dont bother with an engine flush, they can do more harm then good"

So I've gone with that (....) and we'll see how we go - interesting to avoid the engine flush!

[Gazzab]

stuthemong said:

I recently had a service at APM. Andy uses Mobil 1 15w-50 fully synth and I'm not going to argue with the man who built my engine!

As luck would have it, Halfords have it on special at the moment, ( http://www.halfords.com/webapp/wcs/stores/servlet/... ) - I'll just buy a 5L which will do me for a long while to come - can't argue at that price (was about to buy from Opie, but that's £12 dearer due to the offer)

Stu

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[ro_butler]

40 weight should be fine. I did some track days in France in 30+ degree heat this month and the oil pressure was high and stable at hot idle (although slightly lower than in UK).
Also TopCats said 40W has always worked fine for them.

[HarryW]

What about a fuch 5-40 as used by BMW's, check GSF they are around £16 for 4ltr .