Single grade oil and low temperatures

[stefan_r]

My MAN engines come with a lovely list of approved engine oils. In the front it also bangs on a bit about oils and stuff and then goes on to talk about single grade oil.

It seems to be suggesting that the Single Grade 30 oil that is recommended for use shouldn't be used in low temperatures, like around <5deg centigrade.

I am getting ready to do my end of year oil change but am suddenly interested as to why they would say this??

I want to use Single Grade as my gearboxes can onlu use Single Grade 30 oil.

Cheers
Stefan

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[Dave_Snelson]

Firstly, engines have different requirements to gearboxes. The reason that you don't want to use a single grade oil in your engines is that at low temperatures, the engines would be difficult to start. 30 grade oil is only 30 grade at 20C. At lower temps, especially 5C, the oil is very much thicker, so making the starter motor work harder and, more importantly, the oil won't circulate around the engine fast enough at start up.

Multi-grade oils behave like a thinner oil at low temps and a thicker oil at high temps. So you have the best of both worlds. Its all to do with a molecule called a Styrene Butadiene Co-polymer. But you didn't want to know that bit, did you!

<hr width=100% size=1>Madoc Yacht Club
<A target="_blank" HREF=http://www.madocyachtclub.co.uk>http://www.madocyachtclub.co.uk</A>

 

[TonyBrooks]

As a single grade oil gets colder its viscosity (runyness) reduces faster than a multi-grade oil. This causes more - much more drag when starting, so putting a higher load on the starter. There will also be more load on the oil pump and drive whilst the oil is cold. There may also be problems with lack of splash and spray lubrication inside the engine, giving rise to more bore wear.

FWIW I run my Bukh on straight 30 all the year round, but I take great care not to rev it, or put it in gear for a few minutes after starting in the winter, and as its inland based, often gets started with ice all over the marina and a howling north wind blowing.

Tony Brooks

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