Break-in oil, is it really necessary?
 

All the manuals I've read while rebuilding my 74 240d engine seem to mention using a break-in oil for the first 500km or so. Is it a good idea to do this, and if so, what might be a good break-in oil?
Actually, maybe I should also ask the basic question of just exactly what is a break-in oil?
Thanks for your replies




1969 220D w/240D engine

The carmakers haven't used "break in oil" for decades.

I'm not sure what it consisted of, if anything different. I think the idea was probably to get you to change the first fill early, which makes sense.

I just got my Daughter's 300D back together. I had scrubbed the honing grit out of the block, scrubbed it some more, and when I got tired of that, I scrubbed it again.

After that I filled it with cheap 30W oil and a fresh filter, drove it to town and back which is about 44 miles round trip, plus a trip up the road and back. When I got back from town, while the oil was hot and everything was churned up in it, I pulled the plug and let it drain all night in an attempt to get as much particulate that may have been in the oil fro the cylinder walls and rings mating with each other, as I could.

I then put in a fresh filter and filled with my normal Chevron Delo and started driving it. I will change that at about 1,800 miles with it hot again to get out any particulate that may come from the cylinder wall break in.

I would suggest something similar to just get the honing grit, dirt that may have gotten in and lint from rags. If the block was honed and it's too late to really scrub the block before assembly, I might even drain the first fill after about 20 miles which will get it to operating temperature. This is a critical time and if there is a lot of grit, it can spoil the bearings fast.

Best of luck,

I was going to start this same thread today. I am about to get my M103 back on the road and wanted to ask about break-in oil.

I have a case of oil I bought for my 'loose' engine before the rebuild. I will use that for a day, and fill up with some Mobil 1 I just bought.

Thanks Larry,
I tried to scrub the block as much as I could, I even ran rags and pipe cleaners down the oil passages, but I like your idea about changing the first batch of oil really quickly. I'm sure I couldn't get all the grime and grit out.

Guys,

It sounds like both of you are about to crank up those fresh engines. It's great fun. For me there has always been something that I had to work out shortly thereafter. It's just part of the deal.

For that first oil change, make sure you change the filter too.

Good luck,

. . . .Larry, you are priceless. Fact is, I agree with you 100% in all you preach to the others about changing out oil and filters. My brother's advice, as a senior additives engineer with Lubrizol does in fact support everything you say. I have to commend you on your tenacity and taking the time to post such long and informative narratives on this site during my brief time here. Well done Larry and thanks from me !

The break in oil mercedes benz referred to was 10w non detergent oil.
The way I always looked at things goes like this;Mercedes benz has employed hundreds of engineers and pay them quit well I on the other hand have no degree in engineering ,so I do as requested and use break in oil.
A break in oil filter was also suggested!
MF

I don't disagree with Mark at all. But, since they recommend running the original oil a regular interval before the first change, and since they now fill at the Factory with Mobil One or equivalent, I think those days are over.

I think light non detergent oil might be helpfu, but I would want to drain it hot and drain it soon.
Good luck,

Nothing beats a good break-in oil than the first oil change - more than just dirt would come out clean.

Best wishes all,
:)

Thanks all for your replies- I have two break-in filters (got the extra through a confused order), so I think I'll just put the second one in after the intial 40 min or so.

The only thing a break-in oil is for is seating the rings, and since chrome-molly compression rings don't "seat" like cast iron ones do, not longer critcal. If you look at the profile of MB rings, you will notice that none of them have a sharp edge like older cast iron ones had. All flat-faced with radiused edges.

If you can find a real break-in filter (they filter much smaller particles than regular filters), use it, but not for more than 100 or so miles -- low oil flow since they are so "tight".

You will be fine if you use standard oil -- synthetic is a waste! -- and drive a couple hundred miles, no more, before changing it after a rebuild.

You do, after 50 miles or so, want to climb a couple steep hills at low speed in high gear, though -- makes sure the rings seat well, as if the don't seat pretty quickly, they may not. Refering to the oil control rings here --- !

Initial oil consumption may be high -- once it goes down to normal, you are home free!

Peter