Bo, I hope you don't mind, but I posted some of your comments on another forum about synthetic oils, and a guy from the UK posted a nice response with some questions that nobody can seem to answer. I'm just curious as to your thoughts:
"In the UK there are three well-known 'fully synthetic' brands, Mobil 1, Castrol RS, and Shell Helix Ultra. Of these three Mobil 1 has the highest profile, with Castrol RS running close (Syntec is unknown here). Shell Helix Ultra is less well known and less widely distributed. This probably represents the relative marketing efforts (or budgets). Amsoil is not available in the UK as far as I know, but I think Valvoline and Redline my be if you look hard enough.
Mobil 1 for normal use is Tri-Synthetic 0W-40. Castrol RS, until a short time ago, was 10W-60. Apart from any other considerations, I did wonder what chemistry was used to give this oil such a wide viscosity rating. Now RS is 0W-40, just like Mobil 1. Helix Ultra was 5W-40, but this recently changed to 5W-30 (but with a kinematic viscosity of 12.1 cSt at 100 deg C, which makes it hovering on the 30/40 boundary).
I was aware that the carrier oil in Mobil 1 was mineral (why do they use so much of it - up to 20% - when the actual additive package is only 2-4% of the carrier, and why isn't the carrier synthetic?). I wasn't aware that one of the three base stocks in Mobil 1 - if I have interpreted these threads correctly - is also a mineral oil. Does anyone know the mineral to synthetic (including carrier oil) percentage is in Mobil 1? I have also read that Castrol switched from Mobil to Shell as a supplier of 'synthetic' base stocks in 1998, and that both Castrol and Shell use the hydrocracked (hydrocracked, hydroisomerised, slack wax stream, depending on who's telling the story) base stocks so are not really synthetic as we might like to call them. As for the less well known or cheaper brands, who knows?
Oil and filter change intervals in the UK are, for recent cars, between 12,000 to 15,000 miles or yearly (and getting even longer). I run both my cars on a yearly change interval as neither now reaches the 12k interval. Shorter change intervals are not at all common, most people seem to follow the manufacturer's recommendations. I use Mobil 1 in both cars, particularly for its better cold start circulation and for its ability to retain in spec over longer mileages. I'm also a sucker for advertising. Whilst there are advantages in a yearly change, the downside is the astronomical price of the quality synthetics in the UK, at around £34 for 4 litres. As a litre is just over a US quart, this translates to around $13 a quart, tax paid. When I read of the $4 a quart paid in the US I begin to realise that someone is paying through the nose for this stuff.
On a personal note I think that these discussions and the technical details are extremely interesting. As for what oil to use, it's up to the individual to read all this stuff and then make a choice. I don't believe that anyone would see much difference between a high quality mineral or a high quality synthetic oil in normal use. Both types seem to be merging into blends anyway. I don't eat at a certain well-known food franchise because I disagree with it's philosophy and I can get better food elsewhere. Despite what might be seen as disingenuous motives from Mobil I'll continue to use Mobil 1 as there are few better oils available elsewhere."
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".