Synthetic Oil vs Conventional Oil

[RabidRabbit]

Oil gets dirty period. Any effort to extend oil change intervals is not in the best interest of any engine. Storys of long life (mileage) and 20,000 mile oil changes are unfortunatly the same with dino oil. Except no one braggs about it, because it is the NORM. As a mechanic with many mechanic friends It is mainly non-mechanical people who get vastly sold on the concept of synthetics. Its advertising that convinces people it will help. And because they dont understand anything under the hood, putting fancy expensive oil in seems like a way to baby your car. If all you folks are using it than all the myths, lies, advertising,and misinformation seem to be working well.

[Srah 1953]

Originally Posted by Dockhead

Before rushing out to buy synthetic oil for your boat, I suggest reading this:

Oil for yacht engines

Yanmar says that synthetic oil is extremely harmful for their marine engines; this guy Viv Cox, a sailor and professional lubrication engineer, agrees.

My Yanmar (3JH5CE) manual has very specific proprietary recommendation Quicksilver) for the oil to be used in the saildrive but makes no recomendations with regard to mineral or synthetic for the engine oil, only an API grading.

[Dockhead]

Originally Posted by Srah 1953

My Yanmar (3JH5CE) manual has very specific proprietary recommendation Quicksilver) for the oil to be used in the saildrive but makes no recomendations with regard to mineral or synthetic for the engine oil, only an API grading.

Read Viv Cox's article. The API grading says a lot -- probably CD, right? Synthetic oil cannot be CD grade, in fact it's at the opposite end of the scale with far too high a TBN for a cool-running, slow-turning marine diesel engine. Only mineral oil can be CD.

He writes:

"There is a great deal of evidence to show that use of an oil with a TBN that is too high for the duty can lead to several problems, particularly high wear rates of cylinder bores. The effect of high TBN engine oils in accelerating wear rates is well known. Burning high TBN oils may generate excessive deposits on the piston crown. As the piston tilts when moving up and down these deposits become compressed and will form a very hard and abrasive layer, causing excessive wear, mainly in the bore.

"Bore wear has similar detrimental effects as bore glazing, instead of a smooth glaze producing a highly polished surface that leads to poor lubrication and high oil consumption."

http://coxengineering.sharepoint.com...htengines.aspx




So basically what he is saying is that higher grade oils, especially synthetics, are designed to resist high bearing pressures and higher combustion temperatures, and to neutralize the acid which is formed from high combustion temperatures of high performance engines.

Those qualities which are good in higher performance engines are actually harmful in marine engines.

API grade "CD" is an obsolete type of oil which has a very low TBN. It is hard to get now. It has been replaced by grades CF and CF4. Even CF4 seems to cause some problems with marine engines.

A number of service bulletins from Yanmar say never put synthetic oil in their engines.

[Srah 1953]

Hi Dockhead.
Thanks for this. Yanmar specifies CF-4 or CI-4 for my engine. Having read various posts and the Cox engineering site I decided that I would go with mineral oil when replacing my oil recently. I didn't understand the TBN comments in the Cox article! But it is always interesting to read more on the subject.

[sartorst]

Well after two of my high mileage gas engines were changed to synthetic they started leaking oil terribly
I will not CHANGE to synthetic !

[GaryMayo]

Originally Posted by sartorst

Well after two of my high mileage gas engines were changed to synthetic they started leaking oil terribly
I will not CHANGE to synthetic !

I remember walking through a Wal-Mart years ago, and seeing an oil drip mat for sale, from Slick 50 , an oil addictive. I knew synthetics could cause engine oil leaks, a real nuisance, but I was shocked to see Slick 50 admit it by selling an oil drip mat for garage floors.