Synthetic Oil OK in M42?

[flyer92]

I have owned a '92 318i vert since 1999, and religiously used conventional oil in its M42 engine until a certain BMW parts warehouse advised that Red Line synthetic 15W50 would be a better alternative. I have been using it for several years with no problems, but my BMW-certified mechanic advised against it. Now I'm both confused and concerned, given his adamant response, and that he used to build E30s in the late 80s/early 90s. So...before I start draining oil and switching back to conventional, I was just curious if anyone here could provide some advice and/or experience on the issue. Many thanks!

[fresh_TD]

You're fine running 15w-50. I run mobile 1 15w-50 all year round.

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[e30davie]

Ask your "bmw-certified mechanic" for some good scientific reasons for his advise.

[flyer92]

Thanks, Fresh...but not worried about the oil weight. Mechanic was more concerned about the fact that it is synthetic, and the engine wasn't designed for synthetic oil.

[e30davie]

The question is not weather the engine was "designed for Synthetic". The question is weather synthetic is an acceptable substitute for mineral based oil. The answer is i'd almost guarantee anyone who is going to post here is not going to have enough scientific data to back up the question either way.

About the only actual data available is that old engines like extra zinc, but the m42 is shim under/over bucket valves, so i'm not sure if the zinc requirement is that important.

I use mineral oil in my old engines, purely because synthetic is too bloody expensive.

[flyer92]

Agree about the $$$, which is another reason I may go back to conventional. As you mentioned, I would never expect to see scientific data here, but was just curious what our members may have seen/experienced with synthetic oils in this engine.

[jdt10768]

I've been using this in my 318is M42:

https://www.amazon.com/Valvoline-20W-50-VR1-Racing-Motor/dp/B00DJ4FIPQ

and have no issues, but I have no data to validate that it is better or worse than dino oil
Seems to work fine

[flyer92]

Thanks, jdt! This sort of feedback really helps validate what I had already believed. Much appreciated.

[roguetoaster]

A certain BMW parts warehouse advised that Red Line synthetic 15W50 would be a better alternative.

That's just a sales tactic.

Thanks, Fresh...but not worried about the oil weight. Mechanic was more concerned about the fact that it is synthetic, and the engine wasn't designed for synthetic oil.

Oil basically serves one primary purpose, to separate rotating metal surfaces from each other, and secondary uses of cooling/cleaning. It's not at all about design intention, but rather about effective usage, which a rated synthetic will provide.

Agree about the $$$, which is another reason I may go back to conventional. As you mentioned, I would never expect to see scientific data here, but was just curious what our members may have seen/experienced with synthetic oils in this engine.

Cost aside, the only way to know if an oil is working well for your engine is to test the oil multiple times, and decide which product is keeping your engine in optimal condition with your use case.

For me, synthetic is fine, conventional works just fine if it's what your budget allows, but you might want to keep on top of your drain interval. If you want some real data to review you should check bobistheoilguy.

I've been using this in my 318is M42:

https://www.amazon.com/Valvoline-20W-50-VR1-Racing-Motor/dp/B00DJ4FIPQ

and have no issues, but I have no data to validate that it is better or worse than dino oil
Seems to work fine

VR1 did, and probably does still lack the detergents that most oil use to remove contaminants. I am not sure it's a brilliant idea to use it in a street car that gets quite dirty and is supposed to have a very long rebuild cycle.

[bmwman91]

I use Mobil1 Synthetic 15W-50, and I have some actual factual reasons to back it up. The M42, due to its use of flat tappet type lifters, does in fact need an oil that is high in "zinc" content as mentioned above. Specifically, the ZDDP (zinc dialkyldithiophosphates) components are important as they provide better lubricity between the nose of the cam lobes and the lifters as they engage, when high axial and shear forces are generated. Basically, an oil with higher ZDDP content will provide better protection from wear, such as galling and scoring, in this applicaiton.

Why M1 15W-50? Because they publish numbers:

https://mobiloil.com/~/media/amer/us/pvl/files/pdfs/mobil-1-oil-product-specs-guide.pdf

An EPA regulation change in 2008 effectively caused many motor oils to drastically reduce the ZDDP content in their oils, which is really no big deal for newer cars since they were either designed with this in mind, or use a lower-friction valve actuation setup to begin with (such as the M44, which pre-dates the change but has no issues). M1 15W-50 is one of the few products out there that is still readily available and will work as intended with our engines.

Anyway, for the conventional vs. synthetic oil debate...you might as well argue Islam vs. Christianity. It is a debate that has raged among enthusiasts forever, and for the life of me I cannot understand why people get so wrapped up in it. Then again, I feel similarly about politics, religion and a lot of other things lol...at some point you have to make a choice and get on with life / driving!

[Bimmerfan84]

I use Liqui-Moly 10w-40 semi-synthetic with MoS2 (this oil has mineral ZDDP in it) here in Florida on my M42. I was a little cautious about using a thinner weight but I listened to the Liqui-Moly rep and put it in. My engine sounds like a sewing machine, no noises, and runs quickly up to its chipped 7000 rpm limit with GREAT gas mileage. Definitely recommended. The stuff is made in Germany, how could you not?

[jdt10768]

I use Liqui-Moly 10w-40 semi-synthetic with MoS2 (this oil has mineral ZDDP in it) here in Florida on my M42. I was a little cautious about using a thinner weight but I listened to the Liqui-Moly rep and put it in. My engine sounds like a sewing machine, no noises, and runs quickly up to its chipped 7000 rpm limit with GREAT gas mileage. Definitely recommended. The stuff is made in Germany, how could you not?

<-- I think I will try this

"VR1 did, and probably does still lack the detergents that most oil use to remove contaminants. I am not sure it's a brilliant idea to use it in a street car that gets quite dirty and is supposed to have a very long rebuild cycle."

good point, def not opposed to changing, thanks

[willworkfore30s]

When I had an m42, I was told to use Rotella T diesel engine oil...

[nick_318is]

I used Rotella T 15W-40 heavy duty diesel non synthetic for a long time in my last M42. I have a fresh build and have gone full synthetic. Initial oil is the BMW 10w-60 (e46 m3 oil) with a redline zinc additive, I'll switch to mobile 1 15w-50 at my next oil change.

[flyer92]

Interesting about the diesel oil...I would have never thought that would be OK for use in the M42. Speaking of which...Nick, did your engine get rebuilt locally, or did you send it off somewhere? Given the age and mileage on my engine, I'm certain a rebuild or replacement is in my future, and just trying to explore options. Any advice would be appreciated.