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ExplosiveToaster
2014.03.13, 21:44 PM
Something I'm wondering about my GTI: At the last oil change (a bit over 3k ago) I switched to Motul Xcess 8100 5W40 synthetic, wanting to try something thicker since this motor gets a beating every once and a while. I usually use Mobil1 0W40, I don't have any complaints TBH and I usually only need to top it off with the leftover .5qt after 3000 and it's good till the next change. With the Motul, I've actually used the last of the jug a few hundred miles ago when I found the dipstick BELOW the "low" mark. I have another jug being delivered tomorrow because it's already at the "low" mark again.

Aren't thicker oils supposed to burn less? Unless my understanding is wrong, a thicker oil would coat the surfaces better and seal better, and the thinner oil would be easier to slip through and let into the combustion chamber...

EDIT: Another thought just came to mind. Could the leftover Mobil1 and its additives make the Motul break down faster?

joel
2014.03.14, 13:31 PM
that sounds possible to me..

I don't know about thicker oil 'burning less' though. Oil burning happens because of what the engine is doing and less because of the type of oil used, I think.

girdwood
2014.03.17, 04:35 AM
I don't have a good understanding of oils and their makeups, but I would venture a guess that changing oils would cause a larger array of detergents and additives to be present and could possibly introduce a quicker breakdown.

Rabbit 16v
2014.03.17, 18:57 PM
Is the Motul oil compliant with VW recommendations?

ExplosiveToaster
2014.03.20, 18:18 PM
Yes, I chose it from the VW 502.00 list. I'm no oil expert either but it makes sense to me that leftover detergents and additives from the Mobil1 might react with the different set of detergents and additives used by Motul.