mechanic did an oil change with semisynth

[Red Westie]

Or I suppose you might argue that seals go hard and less flexible with age especially when cold so the thinner oil is more likely to leak past than the more viscos type on aged seals.
Yes i accept they are the same viscosity when hot but then the seals are warm and more pliable and in the case of front/ rear mains and camshafts, the lip of the seal has a spring pushing it to seal (which is more effective when the seal it'self is warm and flexible)
As for the hydraulic tappets......the higher cold viscosity helps to retain ellement 'inflation' in those tappets that find themselves 'loaded' (either partially or fully opening a valve whilst resting) The thinner oil is proven to 'leak off' more easily.

Anyhow we have both made our points, don't you think.....

Martin

[axeman]

this whole mineral, semi syn thing is point less. in my mind there is not an argument for mineral oil, any more but people want to live ing the past that is there bussness, try pulling in to a petrol station and try and buy some 15/40 mineral to top up with pound to a piece of poo they wont have any, even well know brands have now stoped producing mineral oil look at castrols range all semi syn from memory. i for one run every thing i own and have owned on semi syn at least, this goes for oil cars and bikes ranging from the 1950's to modern cars and bikes.

neil

[Red Westie]

I agree the right viscosity is getting harder and harder to find...like I say, I'm not really into the whole mineral/synthetic debate, as far as I'm concerned it could be either but it has to be 15W40 as my tappets just don't get on with anything thinner and yes I've tried Quantum Sinta Silver 10W40 and comma's own semi 10W40 both with the same noisey result. Whilst I know there isn't any real harm being done it's embarrassing more than anything.

Martin