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(Fully) Synthetic oil

Guest plesbit

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The trouble with boats, and not knowing much, and trying to learn stuff, is that (to paraphrase Newton's Third Law) for every expert there's an equal and opposite expert. I've had so many wildly conflicting opinions on how to fit a 24v heater kindly donated to me (thanks David) that the heater still remains in the original bag.

The latest problem is oil. We currently run our engines with Delphi premium grade semi-synthetic diesel oil. However our suppliers are no longer able to provide this oil. My dad thinks we ought to look at fully synthetic oil instead (from Valvoline). When it comes to diesel engines he has does know quite a lot and, as former head of a military transport outfit has the benefit of years overseeing a workshop looking after the diesel engined military vehicles. Some of the mechanics that worked for him knew things about diesel engines that half the Broads yards couldn't even imagine. In his opinion fully synthetic oils perform excellently and last much longer and, in particular, still provide high performance at much greater temperatures than mineral oils etc can. Given that running hot is a well known issue with the VP MD32 engines we have he thinks it will provide an extra notch of protection for our engines.

Having run the idea past a boating friend who himself is extremely knowledgeable and rebuilds (marine) engines "just for fun" he thinks it's a very bad idea stating that the 32's were never designed with lubricants of this nature in kind as they simply didn't exist back then. He feels if the engines are worn the synthetic stuff simply won't provide the necessary protection and feels the Delphi semi-synth we are already using is probably the best. So once again I am stuck between two conflicting opinions of people who "know". My dad is off to consult his chief engineer, a former boat owner, and the other guy is off to source a good second hand engine for us to replace the 32's when we kill them (very encouraging). We're not aware that our engines are highly worn, they shouldn't be as they only have 1600hrs on the clock (I know someone else with 12000hrs on his 32's) but they do go through a lot of oil compared to my cars. I don't know whether this is a sign of ware or simply a "feature" of engines from the 1960's.

So I am offering up this opportunity for others to come and cloud the issue further. Perhaps I should have made this thread into a poll?

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Don't know why Simon but bought synthetic for the Mercruisers last year then read the manual. "DO NOT USE SYNTHETIC OR SEMI SYNTHETIC LUBRICANTS", Why I havn't got a clue but I did chicken out and by the quicksilver stuff.


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Personally my ideas on oil in marine engines are more focused on the protection the oil provides when the engines are left idle for some time rather than when used, most modern lubricants (el cheapo stuff apart) carry detergent additives and have good viscosity ranges, lubricant quality etc but the type of additive that clings and coats rather than drains down into the sump is worth having. I imagine your Pater will have thoughts on this as military kit is often idle for long periods, mind you they tend to mothball in such circumstances, Here’s a novel thought, why not use the one Volvo make (or have made) for the engines in question, that’s what I do. :-D

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I can't speak for your engines Simon,

But my father in law has been around Trucks and engines (including Volvo's) for most of his working life being a fleet manager for a major logistics company, now retired.

He swears by Synthetic Oil.

Do you know what year your engines were built (roughly) and I will seek an opinion

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Thanks for the responses. Yes the military like their synthetic oil and it is trucks we are talking about here too Perry - the outfit in question being part of the RCT (Royal Corps of Transport) before the demise of that Corps in army cutbacks.

Unfortunately as the site went down right after the post I couldn't wait for an answer. We've gone with the semi-synth diesel formula from Valvoline. My dad was not convinced that the synthetic that was available was up to the job. We'll use this for this season but are specifically looking at the "clingy" oil types like those mentioned by David for use next time. I dread to think what VP charge for "their" oil but I think Magnotec (sp?) do something similar. Anyway, there's plenty of time to research this before next time.

As an aside, apparently since they went over to synthetic oil the military has now reduced the oil change intervals in their vehicles to once every five years - yes FIVE years. Apparently one of the key advantages is the resistance to break down of mineral oils which was one of the main things putting a shelf life on it in the past. In this respect synthetic oils are a giant leap forward - so I am told.

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In the motor industry modern day engines are built to take fully synthetic oils. The tolerances within the manufacturer of modern day engines are far tighter than engines of circa 15 years ago. Even so, today’s engines that run using fully synthetic oils do use a higher quantity of oil and require more regular top ups compared to earlier engines designed to take mineral or semi synthetic oils. However, the plus side of this is of course far better protection and longer service life between changes.

On discussing this subject with oil manufacturers one of the main reasons why it is not recommended to use in older designed and worn engines is the cleaning additives that reduce carbon build up which in turn lower the compressions within the cylinders. Also due to the larger tolerances, the quantities of oil burnt would be far higher thus increasing overall emissions.

Oils are very hydroscopic (attract water) and oils designed for the marine industry include additives to protect against this, due to the nature of the environment i.e. long standing damp conditions. That is why it is not recommended to use oils designed for the car industry in boat engines.

Volvo Penta dealers stock oils for all their old and modern engines and when I had my last boat which had twin Volvo Penta AQ140 engines I always used their oils and when changed on a yearly basis the oil came out as clean as it went in. Mind you don’t expect this on diesel engines.


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Interesting. I happen to know of a number of manufacturers of various products in various industries, such as some washing powder / liquid producers and paint companies who make identical formulations and poor them into different packaging purely for the purpose of marketing. This one gets your whites white, this one is specifically formulated to prevent bleaching colours, this is special paint for your kitchen or bathroom yadda yadda yadda. I guess I have been exposed to so much marketing bullshit I've become extremely cynical about whether "special formulations" are anything of the sort. I also know from personal experience that a) anything with the word marine in the title costs more B) anything with the words Volvo and Penta in the title cost even more again and c) I've been deliberately misled on more than one occasion by people who recognised my lack experience in matters marine. You can see, perhaps, why I might therefore have been reluctant to go running to Volvo waving my cheque book for their specially formulated marine oil. Indeed, they are already on the list of people who have ripped me off previously and when I eventually got wise to it suddenly credit notes started appearing against outstanding invoices. For those that had already been paid, however, there was no getting it back.

It would seem in this case my cynicism is unfounded, but I believe it understandable nevertheless. In any case it's done now so I'll worry about it again in the Autumn - assuming we've not toasted the engines, of course. ;)

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:wave just a thought if your running twin engines try one on synthetic and the other on the usual oil if you encounter any probs switch to what ever is doing best, personally the only problem i can see is the cleaning adddatives in synthetic removing any carbon build up and thus lowering compresion on the engine some more info on the following links



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Well, as I believe I said, he didn't get the synthetic in the end. And the more I read on it the more I think that was probably a good thing.

However.... he did buy this stuff called Asta 3000 [linky] which is supposed to boost performance on old engines. Whether or not that means old technology or just heavily worn is not clear but the product markets itself for all comers. However it seems to me that it is going to do much the same thing as some of the detergents in the synthetic oil (apparently it "cleans and protects") and so remains a bad idea.

From the "engine oil bible" (http://www.carbibles.com/engineoil_bible.html):

"In an old engine you really don't want to remove all the deposits. Some of these deposits help seal rings, lifters and even some of the flanges between the heads, covers, pan and the block, where the gaskets are thin. I have heard of engines with over 280,000km that worked fine, but when flushed it failed in a month because the blow-by past the scraper ring (now really clean) contaminated the oil and screwed the rod bearings."

Unfortunately I simply don't know enough about it but my inclination is to send it back to him and he can stick it in his car if he thinks it's that great. Any more words of wisdom would be appreciated - the goal posts have shifted somewhat so it'll be another couple of weeks before the service now.

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