Synthetic oil

[Dave_S]

I would always choose synthetic, regardless of the manufacturers recommendations. I'm no oil expert and I know little about diesel engines but in stressed race engines synthetic out performs mineral oil. We had oil samples tested after each event and never had a poor result on the test. When the engines were pulled down annually, the engines had much less evidence of stress even though we extended the use of the synthetic oil sometimes 4 times the miles we used to run mineral oils.

I believe the synthetic has much better properties across a wider range of environments and that's why the engines were better when pulled down.

Note: We did use top end expensive oil which may be different from mid range synthetics.... I don't know.

We never tested the mineral oils, we replaced it always after each event.

Note 2. Some old engines use a cord for a crankshaft seal and may need mineral oil. I know they did use the cord but I'm not sure if it is suitable or not for synthetic oil???

[sailingunity]

Originally Posted by AiniA

My owner's manual and service manual date to 1978 (Volvo MD11C). This is way before synthetic oil existed. The oil they recommend has been obsolete for decades. If we assume you can use newer, non-synthetic oil which you must since the recommended oil no longer exists, it is a valid question to ask about synthetic oil.

Right on, my owners manual suggests single weight oil! I just use 15W-40 in it.