synthetic oils

E

evmars1

Active Member
Joined
27 Nov 2005
Messages
62
Visit site
I have been advised that I should use a synthetic lube oil in my 22year old Yanmar. At the moment I am using CG-4 petrolium based oil.
Will my Yanmar Benefit from the extra cost? or is this guy standing at the bar an "EXPERT"?
 
overwhelming consensus on here previously has been that fairly crude marine diesels only require bog standard oils and that advanced stuff is wasted and may even do some sort of damage.
Somebody else may come in with a reference to the suitable C code which I can't find off hand. Or try a search.
 
I've done a search on oils and have a lot of technical info, most of which is understandable by a petrochemical engineer ie. not a yottie like me! So if anybody can help I would be very grateful.

tvm

David
 
Your 22 year old (probably 30 year old design) will do best on monograde 20 to 30 year old oil technology (so an automotive engineer told me). SAE-30 without any additives turned my old SB-12 from an oil guzzler to a happy smoke free lugger after a few hours.
 
Save your money, just be religious about oil and filter change every hundred hours or at least twice a year if you don't motor a lot.
 
[ QUOTE ]
Your 22 year old (probably 30 year old design) will do best on monograde 20 to 30 year old oil technology (so an automotive engineer told me). SAE-30 without any additives turned my old SB-12 from an oil guzzler to a happy smoke free lugger after a few hours.

[/ QUOTE ]

My post is more to do with my curiosity than anything. I would just like to know why your engine stopped using oil. The whole point of multigrade oil is to thin the oil at low temperatures, and thicken it at higher temperatures. I suppose it is possible the oil you are using is thicker at the low running temperature of these raw water cooled engines. The only reason I'm aware of for using a single grade oil, was because multigrade oils hadn't been invented when this engine was first produced.

Also engine oils contain additives for lots of other things. Catastrophic wear for instance. When the camshaft contacts the follower, far from being smooth surfaces, they are a series of peaks and hollows. Without the microscopic 'ball bearings' in engine oil, the camshaft lobe, and cam follower will quickly be worn out.

I also know every engine, regardkess of condition etc. uses 2/3rds more oil over 3500 revs, than under it. Doesn't apply to these slow revving engines of course.

I do know synthetic, and semi synthetic oils can damage the older type bearings, but does this apply to the 22year old Yanmar. Which engine is it. I suspect it is the one brought out to replace the ancient design of the YS range.

With an engine with severe crankcase compression, due to a broken ring in an engine I ran for a month or two many years ago, using straight oil and driving a little faster used a gallon in 30 MILES. Yet using a good multigrade (Duckhams in fact) on the return journey, with a few less revs, brought it back to 80 miles A PINT.

As I've said, I AM NOT saying you are wrong, just curious as to why your engine has stopped using oil. My YSE12 uses almost no oil, and I use a good mineral 15/50 diesel oil.
 
Most likely explanation is that the older oils can't cling to the cylinder wall quite as well as the synthetics and the oil control ring on the piston can "cut" through it and seal a bit better.

Also, oil consumption on a car depends on lots of things besides engine speed. Throttle position is very important - high vacuum (i.e. over-run) can really suck the stuff past worn valve stem oil seals and guides.
 
Advice from Laverda on a 30 year old motor bike engine, is that the old mineral oils provide better oil mist lubrication (I guess the engine was designed to use this mist to reach some parts) They say synthetics dont provide a mist lubrication as well.
 
[ QUOTE ]

Also, oil consumption on a car depends on lots of things besides engine speed. Throttle position is very important - high vacuum (i.e. over-run) can really suck the stuff past worn valve stem oil seals and guides.

[/ QUOTE ]

Yes. If you get smoke when you have your foot down, oil is being blown back up past the rings, due to high crankcase compression and burnt. If the engine smokes when you take your foot off, the suction is drawing it past worn valve guides and seals.

It is also possible for engines with chrome rings to get glazed bores, which cause them to smoke dramatically.

A common problem with the more modern engine is for them to suddenly loose all oil. This happens when a breather becomes blocked.

I had a high milage Renault Extra diesel van a few years ago. On a long journey it blew all the oil out. I discovered the breather system cycled the oil around, and back into the sump. The large amount of oil must have blocked the outlet breather at the front, causing it to be blown out the back. There was also a small black plastic box in the system, attached to the intake. I'm assuming this acted as a 'spin drier' and deposited the misted oil back in the sump. On the return journey I kept the speed down, with breaks every half an hour or so, and it was ok. I ran the vehicle for another 3 years, and it continued to only use less than a pint in 1000 miles.
 
The gearbox issue is not about multigrade, it's about additives. Motorbike gearboxes use synthetic oils, but specific M/C grade ones that don't have friciton modifiers in them to affect the oil bath clutch
 
I've worked a bit on restoring MG's and fiddling with aged marine diesels. The recurring theme I hear from the trade is that synthetic oils cause rapid shrinking of the older type rubber O-rings, due to washing out of the plasticizer chemicals. Most advocate mineral based oils, or semi-synthetic.
 
Modern oils don;t have the film thickness to protect sloppy bearings on old engine designs. Modern engiens are built much closer tolerances and benefit from modern thin film oils. Old engines need the viscosity of older oils. Straight 30 suits most needs
 
Most older non-turbo charged engines, and certainly Yanmar was one of these, were recommended to use API-CD grade lubricant. This grade is now obsolete and has been replaced by API-CF-4. However, you will find that many of the cheaper types of oil sold in car parts shops, Halfords, etc are still to API-CD. Yanmar's own oil, at least the last that I bought, was to API-CD. My Yanmar 30 is always filled with oil to this grade which is widely available from good manufacturers in French supermarkets.

Turbocharged diesels are required to run on oil to higher grades, such as API-CH-4 and API-CI-4. In order to combat the increased temperatures of these engines, and hence the more arduous conditions at the piston/bore/combustion space interface, the base number of these grades is considerably higher than is required for a non-turbo application. Using high base number oils in a non-turbo may lead to increased wear of bores and possibly cams and tappets.

There is no effect on bearings from using either type, the base oil is the same but the difference derives from the additive package. I can see no advantage in using monograde oils, especially in a boat kept in UK that is frequently asked to start in quite low temperatures but may then run in a poorly ventilated engine compartment at quite high temperatures. A multigrade oil will perform to a far higher standard in these conditions.

Synthetic oils are hydrocarbons produced by techniques that limit molecular chain lengths to a narrow range. This prevents laquering of bearings and other components when the short molecules break down in contact with hot surfaces. Use of these base oils in a non-turbo engine will do no harm (other than the additive package, which will always be to a high temperature specification) but they will give absolutely no advantage.
 
Wife had an MX5 (modern engine) and we had terrible tappet rattling problems. It was a low mileage, low useage car.
Turns out that fully synthetic oil was the culprit. Changed to semi-synthetic and regular oil changes and the problem went away.
I only found out by trawling US Miata (MX5) websites. The hydraulic tappets on these cars are very susceptible. No-one tells you these things.
 
You must log in or register to reply here.

Share this page

Top