Motor Oil

[Rawja]

First, let me admit to being a little...errr..wacky when it comes to maintenance for my Reatta.

I use Mobil 1 synthetic oil and change it religously every 3000 miles.

Anyway, I caught the technician at the garage I use putting Castrol Syntec 10W40 in today when I was getting the oil changed. I can live with not using my preferred brand, but the wrong weight bothered me.

I didn't say anything as the owner and I are friends, and they put up with a lot of picayune nit-picking of their work on my part and have yet to club me over the head with a ratchet, though I know I exasperate them at times.

So, lemme ask you all:

I'm assuming that this won't cause any apprieciable harm to the engine, but isn't the 5W30 going to be a better choice for higher gas mileage, less wear at initial warm-up, etc.?

.....Or am I just being too picky?

[Guest EDBSO]

I think the slightly thicker weight oil is better for summer heat protection.

For -40 the 5w has a big advantage.

I have used Syntec 5W50 in my Reattas. Recently been using WalMart or Valvoline synthetics.

For my next car it will be Mobil 1 only.

[padgett]

I use 10w30 all year round. Unless there is a problem with oil pressure there is no reason for a heavier weight and do not forget that "weights" (actually viscosity) is non-linear and inside a range+ 30 is between 9.3 and 12.5 centistokes at 100C and 40 is between 12.5 and 16.5 centistokes. This can be quite a big difference and the difference adds both drag and heat generation, neither of which are good for the engine.

So unless there is a problem with oil pressure (spec for a "C" is 40 psi at 1875 rpm and mine run around 50 psi there) or circulation, there is no reason to run anything except 10W30 unless the temperature is going to be significantly below freezing and then 5W30. (SAE measures the Winter rating at -18C).

[Booreatta]

From all of the research that I have seen the above post is right on

at summer temps the higher vis at 40 would be somewhat better than 30

the lower end of 10 wont make any difference in warm temps...now in the winter

the 5 vis is prefered due to the fact that is is thiner in cold temps and will lube somewhat faster thus less friction and wear at freezing temps. On the other hadd the 10w40 is great for hot weather.

your mechanic is looking after your car ok

[jonlabree]

Buick recomends ONLY non-synthetic oil.

They frown down on all synthetic Oil.

But, to each his own...

JON...

[jonlabree]

Buick recomends ONLY non-synthetic oil.

They frown down on all synthetic Oil.

But, to each his own...

JON...

[2seater]

Actually, the manual recommends 5w-30 only if the temperature drops below zero F. Above zero, 10w-30 can be used and if always above 60 deg.F, straight 30 is acceptable. I haven't found straight 30 in pure synthetic yet. Our engine uses tight clearances on the bearings and "fatter" oil isn't needed unless oil pressure is a problem. That crank driven oil pump spins twice as fast as more conventional types, and usually oil pressure is not a problem. My turbo does steal some of my oil pressure so I have gone to 5w-40 Mobil 1. I have searched the manual and I do not find any recommendation of synthetic vs conventional oil as long as it meets the minimum specs, and everything commonly available today is light years beyond where they were 15 years ago. All oils are pretty good.