oil grade

[eric]

What's the worst that would happen if I put in 15w40 instead of 5w40 the manual recommends? I change oil twice yearly, should I buy the correct oil now to change now, then use the 15w40 next time ( eg in six months when most cold weather is gone).

its a 1.5 dci

Ta!

[Wickydude]

Worst that would happen is speeding your turbo on its way to the eternal highway in the sky.
Especially when cold, turbo engines want nice and thin oil. Wrong saving.

[AlexB]

OEM oil is just £28 with free delivery.
https://www.amazon.co.uk/Elf-Evolution-S ... B00M5ZDPA0

[eric]

Alex thanks for the link.

Is there any way I could mix what I have now with another grade to bring it closer to the grade needed? I'm thinking 0w40 with 15w40 would end up closer to what is required, or does it work that way? I just don't want to waste what I have now.

I will of course use the proper grade next time

[Wickydude]

It's not just about the viscosity. It's also about the correct formula (additives) of the oil.
Especially if you have a DPF, the wrong oil can cause the DPF to clog sooner than necessary, resulting in extra regeneration cycles, and ultimately early death of the DPF.
oil is the only thing keeping metal parts from touching each other. I'd really recommend getting the correct spec. IMHO it's not worth the saving in oil compared to the cost of engine troubles.

Have a read through this:
https://www.carbibles.com/engineoil_bible.html#

[AlexB]

No, please don't mix them on purpose. They are compatible only in the sense that their mix will not solidify or catch fire straight away. The mix is likely to turn up worse than each of these oils taken separately, at least not much better than the cheapest one.

The reason why you may not want to mix a 0w40 with 15w40 is that the main advantage of the former oil is its PAO basestock, which is thermally stable, not leaving burnt residue on hot surfaces while being not good in boundary lubrication - so, it requires plenty of very specific additives. A 15w40 oil has a mineral basestock, which is average in lubrication and prone to leaving burnt residue/sludge everywhere while being not as thermally stable as PAO. These two basestocks are so much different, that they require completely different compositions of additives to alleviate their shortcomings. By mixing these oils you may arrive to a reasonable initial viscosity, but it will deteriorate quickly with use, residue on pistons and turbo shafts will appear and the mix will not withstand the soot loading usual for turbodiesels with EGR.

If you have access to cheap/free 0w40, then most of such oils are MB229.5, which makes them suitable for your engine. One can use a 15w40 only for topping up in an emergency, then it has to be changed as soon as possible.

Actually, the oil viscosity grade is not as important as ACEA, Mercedes or Renault specs, the latter two being more strict than the former. Any oil with RN0710 or MB229.5 on the label is suitable for your engine.

Careful with the car bibles in the previous post. They suggest that a semi- version of a 15w40 can be used to increase the oil change intervals. It is not true for the turbodiesels with EGR. EGR causes increased soot loading, so at the end of its life the oil may contain more than 3% of soot. It causes thickening, sludge formation, dirty oil bypassing the oil filter, etc. For this application one needs an oil resistant to thickening, not thinning (as in performance petrol engines).

[eric]

OK thanks for that, its convinced me to get the right stuff