Synthetic oil: Diesel mechanic says no - PeachParts Mercedes-Benz Forum

benedict · #1 08-04-2011, 04:46 AM

Hi,

I was hoping to treat my engine to some quality oil...
Diesel mechanic (of some 30 years) says that an engine over 100,000km/60,000miles should stick with mineral. I asked why? and he said it was because the main bearing clearances would not like the thin oil and not good for timing gear either.

Should I stick with the mineral oil (currently using 10w/40)? or move to synthetic and hope for the best?

Any input will help me to make a decision.

Thanks,

1994 E300 diesel: OM606.910 NA (233,000kms/145,000miles)

oldsinner111 · #2 08-04-2011, 04:52 AM

you should be running 15w40 diesel oil.I tried syn. oil in my diesel and it leaked at a few places.

Stretch · #3 08-04-2011, 04:55 AM

It is pretty difficult to get mineral oil here - well you can buy the classic car stuff at a premium but I don't think they do diesel classic oils... I only use synthetic specifically-made-for-diesel oils.

strelnik · #4 08-04-2011, 06:42 AM

Quote:

Originally Posted by Army

It is pretty difficult to get mineral oil here - well you can buy the classic car stuff at a premium but I don't think they do diesel classic oils... I only use synthetic specifically-made-for-diesel oils.

Rotella should be everywhere, right?

It's made by Royal Dutch Shell....And you can't find it in NLD?

75Sv1 · #5 08-04-2011, 07:21 AM

I am usaully a fan of synthetics. I do think there is still some performance/protection gains to using a synthetic. I do not understand at 60,000 miles, especially for a diesel. Diesel motors are usually built better than gasoline motors. Higher compression so they have to be.
I would say that the main concern would be that the synthetic might clean out dirt deposits and then you might have oil leaks. Still, if your present oil is clean, then it should be OK to switch.
I know Rotella has 10W-30, 10W-40 and 15W-40 diesel rated oils. They are conventional oil or possibly a semi-synthetic. I didn't look at your sig to see where you live. I'm in IN. I run 15W-40 from spring to fall. Then I run 10W-30 Rotella during the winter. I don't drive the 240D much during that time due to snow and salt, if at all. I'd check your manual as to what viscosity to use as to tempertures.
Mercedes speced Synthetic oils at least from 2000 on. There was a class action suit over it. If I remeber right MB gave extended warranty for the use of synthetic oils.
Tom

compu_85 · #6 08-04-2011, 08:25 AM

All of my diesels... from the 50,000 mile engine in my SDL to the 425,000 mile engine in my friends 91 Jetta, get 5w40 synthetic oil. If synthetic causes a leak it was because a seal was bad anyway.

Let alone the conventional / synthetic debate... 10w40 is the wrong grade for your car. Most 10w40 oils are not rated for diesel service. If you must use a conventional oil use a 15w40.

Shell Rotella 5w40 is an excellent oil. The reformulation that happened a few years ago makes it that much better.

-J

Stretch · #7 08-04-2011, 08:49 AM

Quote:

Originally Posted by strelnik

Rotella should be everywhere, right?

It's made by Royal Dutch Shell....And you can't find it in NLD?

It only seems to be sold in very small packages in shell fuel stations here (and I'm not sure that the mineral stuff is widely available).

In "the shops" it is mostly Castrol - sometimes Mobil. In the motor factors it is mostly Kroon.

The Netherlands isn't a country of choice. If they have one brand they tend to stick with it - very much the attitude throughout the whole country. I often walk into the supermarkets over here and end up thinking - oh well steak and chips just like everyone else then...

When we visit the UK or the US we are always gob smacked when we see whole isles dedicated to just toilet paper! Or just cheese! Or just Chicken! (you get the picture?)

boneheaddoctor · #8 08-04-2011, 09:01 AM

I only glanced through every post but want to say why it's usually a bad idea to switch to synthetic over 100K miles if all its had was Dino.

Synthetic is very good to cleaning crud out of the internals.....and the problem is at higher mileage those deposits have built up on seals and many times are whats keeping those seals from leaking. Introduce synthetic at that time those deposits get cleaned out and you can end up with seals that are now ill fitting and you start finding leaks you never had before. And the only way to stop those leaks is new seals. Not everyone might have that happen...but if you are one...that's no small job.

That's not meant to slam synthetics at all....far from it. Its only to point out there can be a downside to switching to a synthetic. And many of these have gotten to 300k, 400k and even past 500k (but rarely without a new timing chain or valve job) on dino oil.

Daman858 · #9 08-04-2011, 09:26 AM

There are as many opinions about this as there are mechanics.

I use Rotella (Shell) 5W40 synthetic in my diesel Ford truck and my '79 300CD. No problems or leaks in 290,000 combined miles. I will keep on using it. That horrible low sulfur fuel is another story.

jeffr0000 · #10 08-04-2011, 09:56 AM

Quote:

Originally Posted by Army

When we visit the UK or the US we are always gob smacked when we see whole isles dedicated to just toilet paper! Or just cheese! Or just Chicken! (you get the picture?)

Trade ya my isles of cheese for your beautiful and functional cities.

As for syth vs dino, I trust what Blackstone Labs has to say about it.

Quote:

Originally Posted by Blackstone Labs

What's the best oil to use?
Ah, the million dollar question. We are an independent lab, so we don't make recommendations. It has been our experience that oil is oil, and either petroleum or synthetic-based oil will work well for just about any engine.

http://www.blackstone-labs.com/faq.php

If you really want to experiment with oils or are concerned the oil you use isn't adequate, I highly suggest you start doing used oil analysis.

Matt L · #11 08-04-2011, 10:00 AM

Quote:

Originally Posted by boneheaddoctor

Synthetic is very good to cleaning crud out of the internals.....and the problem is at higher mileage those deposits have built up on seals and many times are whats keeping those seals from leaking. Introduce synthetic at that time those deposits get cleaned out and you can end up with seals that are now ill fitting and you start finding leaks you never had before. And the only way to stop those leaks is new seals. Not everyone might have that happen...but if you are one...that's no small job.

That's not meant to slam synthetics at all....far from it. Its only to point out there can be a downside to switching to a synthetic. And many of these have gotten to 300k, 400k and even past 500k (but rarely without a new timing chain or valve job) on dino oil.

I do not agree.

I think there are two modes here:

1- people who have leaks, switch to synthetic, then LOOK for leaks.
2- people who have seals that are about to go.

I do not believe for a minute that any crud stops leaks.

I've switched many engines to synthetic. Some with over 100K. I like keeping the insides clean.

Stretch · #12 08-04-2011, 10:14 AM

Quote:

Originally Posted by jeffr0000

Trade ya my isles of cheese for your beautiful and functional cities.

...

Done! Sold to the man with 4 zeros in his user name!

sixto · #13 08-04-2011, 10:16 AM

I have no credential to do so but i disagree with your mechanic. Synthetic oil is only relatively thin when cold. Mineral oil at operating temperature flows like synthetic oil. I would argue that mineral oil is too viscous to properly lubricate a cold engine if it's just right at operating temperature. Bearing clearances are tighter when the engine is cold.

Sixto
87 300D

Stretch · #14 08-04-2011, 10:21 AM

Quote:

Originally Posted by sixto

I have no credential to do so but i disagree with your mechanic. Synthetic oil is only relatively thin when cold. Mineral oil at operating temperature flows like synthetic oil. I would argue that mineral oil is too viscous to properly lubricate a cold engine if it's just right at operating temperature. Bearing clearances are tighter when the engines cold.

Sixto
87 300D

And Mercedes engine bearing clearances are a bit tighter than some other manufacturer's engines of the same era... perhaps this sort of advice comes from the days long gone?

boneheaddoctor · #15 08-04-2011, 10:23 AM

Quote:

Originally Posted by Matt L

I do not agree.

I think there are two modes here:

1- people who have leaks, switch to synthetic, then LOOK for leaks.
2- people who have seals that are about to go.

I do not believe for a minute that any crud stops leaks.

I've switched many engines to synthetic. Some with over 100K. I like keeping the insides clean.

Lot of professionals and mechanics will say you are wrong. As well as a lot of people that switched after 100K+ miles of dino without a drip to start having leaks all over.

You don't NOT notice leaks if you have your own house and own driveway....particularly if its concrete.

Just because you were one of those lucky enough to NOT have a leak start doesn't mean nobody else does or has.

Besides....why switch at over 100K? why not start after break-in.

I've got no sludge in mine on Dino oil...at over 200K. Because I change mine religiously on time. every 3,000 miles. Yeah...IF I paid for oil analysis I could likely get a lot longer....but that costs money to find out as well.