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Mr B
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Post by Mr B »

This old cherry :roll:

I have some semi synthetic 10/40, do we think it's a good idea to pour it in my 155,000 mile N/A diesel? It doesn't burn any oil, or should I stick to a 15/40 mineral?

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Post by sleepy0905 »

I would stick to the 15/40 i have just changed from a 10/40 oil back to 15/40 after the oil resembled black treacle and it was only changed the beginning of december but it was too thick.
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Post by DavidRutherford »

Personally, I think it's far more important to change the oil regularly than to be massively concered about the exact spec of the oil.

I've always run XUD engines on 15w-40 mineral oil, but then that's mainly because I buy it in 205 litre (45 gallon) drums. I also tend to change my oil very frequently, but at about £4.50 per sump-full, it's not a problem. I do, however, only change oil filers every other oil change. My reasoning for this is that I probably change oil far too frequently (is that possible?) and that the more used a filter is, the better it filters.

Conversely, I've just finished doing an engine change on a Pug Expert, with an XUD9, that had obviously not had it's oil changed in about 3 years. It was like tar, and the engine was in a very sorry state. All the piston rings had siezed in place, and the oil in the little-end-bearings was like glue. The camshaft was rather amusing too, as it had begun to wear at the bearing surfaces, and had several miles of play!

If anyone is near enough to me, and would like some very good quality 15w-40 mineral oil for a squid-a-litre, then they are welcome.
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Post by jeremy »

The figures in the grading refer to its behaviour at different temperatures - so 15w-40 means that at the cold measuring point it flows like a 15 grade straight oil and at high temperature it behaves like a 40 grade. A 10w-40 will behave like a 10 grade when cold which means it will flow easily and make starting easier, and will circulate your cold engine a little more readily than a 15 grade.

So yes it won't do any harm and may be beneficial - as the engine will use the 40 'bit' most of the time and always when under heavy load.