synthetic oil vs semi-synthetic

derhammer · 20th April 2008, 18:49

Hi,

I am a bit concerned, I went to a independant bmw specialist and he did my oil change with semi-syntetic motul 15w50 oil. I always used castrol tws 10w60 in my engine.

He told me the tws I was using, was useless in my engine because it was designed for the latests bmw m power engines. He told me the motul oil was better suited for my car and that i was paying to much for the castrol tws. My concern is the change from synthetic to semi synthetic... Am I doing something wrong?

AfricaOffroad · 20th April 2008, 19:11

A semi synthetic has a small percentage of Group 3 base oil in it - 10-20% IIRC.

Full synthetics comprise 100% Group 3 or Group 4 base oil. TWS is formulated with Group 4 (PAO).

TWS cannot even be compared to a Motul Semi Synthetic, the former is way way better in its lubrication properties. By way of example, normal group 1 base oil costs $1300per Ton. A group 3 costs about $2300per ton and a group 4 about $ 3500per ton. If oil companies could get the same lubrication properties with group 1s, believe me we would .

You dealer obviously has the Motul in stock - bulk or in 210L drums. He naturally wants to sell it to you.

derhammer · 20th April 2008, 19:19

Quote:

Originally Posted by AfricaOffroad

A semi synthetic has a small percentage of Group 3 base oil in it - 10-20% IIRC.

Full synthetics comprise 100% Group 3 or Group 4 base oil. TWS is formulated with Group 4 (PAO).

TWS cannot even be compared to a Motul Semi Synthetic, the former is way way better in its lubrication properties. By way of example, normal group 1 base oil costs $1300per Ton. A group 3 costs about $2300per ton and a group 4 about $ 3500per ton. If oil companies could get the same lubrication properties with group 1s, believe me we would .

You dealer obviously has the Motul in stock - bulk or in 210L drums. He naturally wants to sell it to you.

Ok, thanks!.. but am I doing any wrong to the engine by running with that oil or should I switch to TWS again?

AfricaOffroad · 20th April 2008, 19:30

Look if it were me, I'd replace it as soon as convenient to do so.

Providing you are not driving your car hard, running up to the red line, or tracking your car, its probably okay. That said, that not how one drives a //M car is it?

davidoli · 20th April 2008, 19:46

Fantastic response .......For a minute , I thought this was going to turn into another one of those inane oil threads .

It's suprising how many mechanics will base their advice on what suits their own purposes ........ thank god he didn't have a barrel of Planet oil in house !

Dan Kelly · 20th April 2008, 19:47

I have been advised by someone who really knows their stuff that they have seen accelerated wear in S38 engines with 10w60 oil. BMW recommend 10w40 or 15w50 oils for this engine, I would stick to that.

derhammer · 20th April 2008, 19:49

Quote:

Originally Posted by Dan Kelly

I have been advised by someone who really knows their stuff that they have seen accelerated wear in S38 engines with 10w60 oil. BMW recommend 10w40 or 15w50 oils for this engine, I would stick to that.

even if the car used synthetic oil in the past?

Dan Kelly · 20th April 2008, 19:53

I would still use fully synthetic oil for the reasons stated by AfricaOffroad but would avoid using 10w60 and stick to recommended ranges.

AfricaOffroad · 20th April 2008, 19:58

Quote:

Originally Posted by Dan Kelly

I have been advised by someone who really knows their stuff that they have seen accelerated wear in S38 engines with 10w60 oil. BMW recommend 10w40 or 15w50 oils for this engine, I would stick to that.

Was that Raymond with the excessive cam lobe wear issue? If so, I suspect this relates more to the fact that occasional use allows the top end and oil channels to fully drain. On start up, top end could be a little oil starved for a few seconds.

If I lived in a cold climate, UK, Canada etc I'd definitely run a 0W?? (30 or 40), not a 15W. But it would be full synthetic (Group 4 based first choice, although 3 is also good stuff)

davidoli · 20th April 2008, 20:08

IIRC it was one of the BMW Motorsport division guys in Germany that recommended the use of Castrol Edge / TWS 10W60 specifically for the S38 engine .

Do you mind me asking who suggested otherwise to you ?

We need to consider that oil technology has moved on vastly from 1995 when the last of these S38 engines were put into E34 M5s and the owner's manuals produced .