Oil. 15W40 vs 25W40...and a 1GM10

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vertford

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In my excitement to get going after my oil filter change, I noticed I had used all my Yanmar 15W40 oil up.

A rummage has revealed I have some Quicksilver Sterndrive 4 Cycle engine oil SAE at 25W40. Can I use this to top up my Yanmar oil as I need about half a litre?

The nice chart in my diesel book by that French bloke seems to indicate that
20W50 is more viscous at higher temps: 50 degrees on the chart. Don't really understand the first figure...

Thanks
 
vertford said:
In my excitement to get going after my oil filter change, I noticed I had used all my Yanmar 15W40 oil up.

A rummage has revealed I have some Quicksilver Sterndrive 4 Cycle engine oil SAE at 25W40. Can I use this to top up my Yanmar oil as I need about half a litre?

The nice chart in my diesel book by that French bloke seems to indicate that
20W50 is more viscous at higher temps: 50 degrees on the chart. Don't really understand the first figure...

Thanks
Click to expand...

The second figure relates to the viscosity at running temperature - about 100C so, yes, 20W50 will be more viscous than 15 or 25W40. The first figure relates to cold start conditions so a low figure will assist fast cranking and also rapid circulation around the engine - hence less wear. As for mixing the two - can do in an emergency but best avoided if you can get more of the original Yanmar oil. An engine's an expensive bit of kit so it's worth being fussy about the oil.
 
I wouldn't use that oil unless it's an emergency, that is a different viscosity(not by much admittedly) and it would appear to be for a petrol engine(quicksilver is mercury's own brand isn't it?). Oils for petrol engines don't cope well with the **** that diesels dump into their sump oil. Better to get some generic diesel 15w40(not synthetic unless you like wasting money) from a motor factors(halfords' own brand is reasonably priced) and have plenty spare. Buying 15w40 with Yanmar written on the bottle is a waste of money.
 
25W/40 is fairly viscous and for a small engine like a 1GM10 might give some circulation problems on first starting from cold. As an emergency top-up it will be better than nothing but as you are clearly not in that situation I would buy something more appropriate.

You have not told us the other important parameter of the oil, which is its API classification. There is plenty of information about this on my website under' engines'. This will also tell you whether it is intended for use in diesel engines (C for compression ignition) or petrol engines (S for spark ignition) or both.
 
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