Mixing engine oil?

C

ColinR

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www.victoriashadow.co.uk
I've got some left over of two makes, not enough of each to do an oil change unless I mix them but I wasn't sure if its a good idea. They are Volvo and Starbrite, both 15W40 API CG4.

One is several years old, not sure if it deteriorates with age.

thanks! Colin
 
It is a condition of compliance with the specification that oils from different manufacturers will mix without negative effects. Test mixing is normally 1:10, 50:50, 10:1. Oils should not deteriorate in a closed, inert container.
 
Mixing oils

vyv_cox said:
It is a condition of compliance with the specification that oils from different manufacturers will mix without negative effects. Test mixing is normally 1:10, 50:50, 10:1. Oils should not deteriorate in a closed, inert container.
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Second that.

All engine oils of similar spec.
 
Anybody know does the same thing apply to 2 stroke oil?
Could I safely mix mineral Quicksilver with synthetic Shell Nautilus without causing any problems? They are both TCW3.
 
theoldsalt said:
I would not mix mineral and synthetic oils.
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In this context 'synthetic' simply means that the oil was not distilled from crude oil, but synthesized from hydrocarbon gases. The advantage of this is that molecular length is more closely controlled, limiting gums and oily deposits. The ash content of 2-stroke oil is thus reduced. Not to be confused with synthetic hydraulic and other oils that are not hydrocarbon based.

I don't have the experience to answer the mixing question but I would be surprised if there was a problem.
 
From one of Shells data sheets for Nautilus outboard motor oil

"Compatibility - Nautilus is fully compatible with all other TC-W3 and TC-W II lubricants to eliminate any risk of operating mishaps"

No problem therefore with mixing them.
 
Hi all,

Perhaps I should have written "I do not mix mineral with synthetic"

I was not intending to give advise, merely expressing my preference.

As some minerals can be mixed with synthetic and some should not, to save any possibility of a mistake, on my boat they are not mixed.
 
Haydude,

Viv Cox might be a better source of info but here are my thoughts.

Many of us use engines that are many years old. Mine is over 20. These engines were designed to run on mineral oil. Relatively newer engines, especially marinised vehicle engines have been designed to run on synthetic.
It may be possible for older engines to be run on synthetic if all traces of mineral oil are removed first, especially sludge that has built up over the years as the synthetic oils can 'clean' the engine and dislodged sludge may block oil ways and cause engine failure. But there may be a problem with seal compatibility.

However I see no reason to change from mineral oil on my engine as long as it is still readily available. The basic mineral oils are at present cheaper than modern synthetics.

However I do not know the consequences of mixing mineral and synthetic together at the same time in any particular engine and I see no reason to experiment. I stick with the tried and trusted in my old engine.
 
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haydude said:
That is what I was told as well. But could anyone explain why?

And why we cannot use synthetic oils with our diesel engines?
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There is some info on my website here. As I said a couple of posts up, the difference between the base oils of mineral and synthetic lubricants is that the molecular length of the mineral grade is very variable, whereas in a synthetic it is much less so. Synthetics are made this way to reduce gum and carbon deposits in high temperature engines, reciprocating ones in this context but there is a parallel case for gas turbines, where mineral oils simply will not run in high power industrial machines. (Not aero engines, which use synthetics that are not hydrocarbon based, giving them hugely increased high temperature stability.)

However, it is in the additive packages that the main differences occur. In the 1950s engine lubricants contained no additives whatsoever. Gradually as engine power increased it was found that anti-oxidants and anti-corrosives improved the life of oils, lubricant grades of API CC and CD (specified for many of our auxiliary engines) having little more than these two. As automotive powers went up it became necessary to add more and more additives, so that a modern high performance road lub has an additive content of around 25%. Reductions in the sulphur content of road fuels has also required changes to the lubricant, particularly to the base number. The API classifications at the bottom of my website page give much information on this subject. There is a good deal of experience demonstrating that use of these high performance oils in older, low power yacht engines does them no good at all, especially in promoting bore wear.
 
I have two oils Cespa left over 3 litres and 12 litres of Rimmula Rx3 This is the perfect amount for the engine. Can I mix both of these 15/40 oils together. Both have the specs individually to work in the engine. Your thoughts would be great to have.

I dont have the containers to test mixing them. If I did as mentioned in another post above how long do you leave them?

cheers
 
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Jamesuk said:
I have two oils Cespa left over 3 litres and 12 litres of Rimmula Rx3 This is the perfect amount for the engine. Can I mix both of these 15/40 oils together. Both have the specs individually to work in the engine. Your thoughts would be great to have.

I dont have the containers to test mixing them. If I did as mentioned in another post above how long do you leave them?

cheers
Click to expand...

I think Vyv has answered the question in #2 above.

I suspect the mixing tests Vyv refers to are more than checking that the two physically mix. You could do that in a jam jar!
 
VicS said:
I think Vyv has answered the question in #2 above.

I suspect the mixing tests Vyv refers to are more than checking that the two physically mix. You could do that in a jam jar!
Click to expand...

As I leave on Sunday it would seem a terrible waste of Jam, instead I just bought enough oil for the change and will use the majority quantity for the Generator and the minority as mentioned will give to a smaller boaty.
 
VicS said:
I think Vyv has answered the question in #2 above.

I suspect the mixing tests Vyv refers to are more than checking that the two physically mix. You could do that in a jam jar!
Click to expand...

They use measuring cylinders, not jam jars, but at this level of research it is simply checking that there is no deposition of reacting additives, very obvious as milky sludges.
 
haydude said:
That is what I was told as well. But could anyone explain why?

And why we cannot use synthetic oils with our diesel engines?
Click to expand...

Synthetic oil is not recommended for yatch engines. It's designed for automotive engines which have a vastly different operating regime. Car engines vary speed a lot and are anyway higher revving, Yatch engines tend to chug along at 12-1500 rpm for extended periods.
Vyv has described it well HERE
 
vyv_cox said:
They use measuring cylinders, not jam jars, but at this level of research it is simply checking that there is no deposition of reacting additives, very obvious as milky sludges.
Click to expand...

not everyone has measuring cylinders handy. I have, presumably you do too, but almost everyone can find an MT jam jar or similar
 
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