Hello to everyone, since this is my first time writing in this forum. recently i bought a 1995 E320 and a 1987 190D from a guy who worked himself on the cars. I plan on doing the same thing, and this weekend I want to change oil and filters on the E320. From looking in his receipts, he used the same oil type on both the 190D (which is a diesel) and on the E320. The oil he used is Mobil Delvac 15w40, which is for diesel cars as far as I know. The E320 engine has been running on this oil for a few years as the receipts tell me. I live in an area where it snows 3 months a year (South Dakota). Should I continue to use this oil, or change to a 10w30? I don't really want to change the oil brand since it always has used the same oil, but if I have to than I will. Also sometimes when I turn on the E320, i hear this little knocking noise (like the noise a diesel makes, but not as loud), not always, only sometimes, especially in the mornings. Could it be from the oil or oil filter (it has Mann oil filter in it, and that's what I plan on using in the future), or is this normal for its age/mileage? Other than that the car is in top shape. Any comments would be greatly appreciated.

moss,

the 15w40 will be fine down to 5 degrees Fahrenheit. if it gets colder than that, 10w40 will be good down to -4.

mercedes recommends 5w50 for all temps for your E320...which would mean switching to synthetic.

you'll probably get about 8 million different opinions but i'd say you're fine sticking with the 15w40, that is unless you see temps below 5 degrees.

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Thanks Ozawa for your reply. I do actually see temperatures below -5, only a few days though. But the owner before me had the car in the same area. I know that it will still start at temperatures below -5F, but is it possible to damage anything like an oil pump for example? Also i don't really want to switch to synthetic. The engine has only seen dino oil in 12 years, and switching to synthetic doesn't seem the right thing to do.
What about the knocking sound, any comments?

Huh?? Where would one find this recommendation?

Those commercial-grade oils like Delvac and Rotella are the best, diesel or gas.

OTOH, I've always used Walmart Supertech with excellent results.

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2012 E350
2006 Callaway SC560

Factory service literature.

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True. For that model, 0W-40, 5W-40, 5W-50 can be used at all temperatures. As a matter of fact, even 0W-30 and 5W-30 can be used at all temps. This is from the 2006 approved service products brochure.

So what do you guys think, Delvac 15w40 will be ok for the cold days in January-February, or should I change to a 5w40 grade?

Please provide a copy.