10w-40 vs. 15w-40

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The Critic

The Critic

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This is an extension of my earlier thread regarding oil for my E30 325.

In my area, my temperatures range from 50 to 70F all year. The manual recommends 10w-40 for this car in temps up to 68F, but 15w-40 is the ideal oil for all temps, per the manual.

A lot has changed in oil technology since those recommendations were made in the 80s. 10w-40 is more commonly available and gives far more choices (High Mileage, Blends, Full Synthetics) than 15w-40.

Is there any good reason why I should choose a 15w-40 over a 10w-40? So far I haven't.

Thanks.
 
Originally Posted By: Nick R
Personally, I'd probably use Mobil 1 0W-40 in an application that calls for 40wt, but doesn't require HDEO


I will be changing it every 2-3k anyway, and I would like to minimize the risk of developing additional oil leaks.
 
Originally Posted By: The Critic
Originally Posted By: Nick R
Personally, I'd probably use Mobil 1 0W-40 in an application that calls for 40wt, but doesn't require HDEO

I will be changing it every 2-3k anyway, and I would like to minimize the risk of developing additional oil leaks.

M1 0W-40 won't creat oil leaks.
Another option if you can find it is PU Euro 5W-40.
Both these oils are actually heavier than you need.
BTW, take a chance and extend your OCI to 5,000 miles or 3 years whichever comes first.
 
15W40 is a traditional diesel grade. This oil has made it's way in to the classic car circles. It works great in older vehicles and is resistant to shearing. I would have no qualms in using it in any of my current vehicles in temps above 45F.

However since I no longer own a classic car it isn't an oil I would go out and buy unless I got a real deal on it.
Shell Rotella has worked very well in my motorcycles as well. Great UOA's
 
Critic, trust me on this.
For an old BMW, M1 15W-50 is the perfect oil.
I ran it for 6K last summer.
Consumption was really low, and the kind of leaks that leave drops in the driveway or garage never happended, which is not the case with Maxlife 10W-40.
Run M1 15W-50 and change it every 6K or once a year.
In my experience, it is the ideal oil for an old BMW which will have oil leaks and will have oil consumption.
I ran a 15W-40 HDEO the summer before this past (Castrol Tection Extra) for 6K, and had noticeable leaks, consumption of a quart every 1500 miles, and 29 mpg. With M1 15W-50, I had no noticeable leaks, consumption of a quart every 2200 miles, and 31 mpg.
Your car, your choice.
 
I have that car with the 2.5L. The person I bought the car from used Pennzoil 10W-40 and the engine was pretty dirty.

I've owned the car 5 yrs, I use M1 0W-40 or Rotella T6 5W-40 and they cleaned it up nice without leaks.
 
MAXLIFE10W-40.jpg
 
Originally Posted By: CATERHAM
PU Euro 5W-40.


Who sells this? Does Walmart or any autoparts chain have it?
 
Originally Posted By: Cristobal
You must live around Eureka or Fortuna, am I right? But if you travel much you wll get to a clime where it can be freezing or awfully hot.


Monterey.
 
Originally Posted By: The Critic
This is an extension of my earlier thread regarding oil for my E30 325.

In my area, my temperatures range from 50 to 70F all year. The manual recommends 10w-40 for this car in temps up to 68F, but 15w-40 is the ideal oil for all temps, per the manual.

A lot has changed in oil technology since those recommendations were made in the 80s. 10w-40 is more commonly available and gives far more choices (High Mileage, Blends, Full Synthetics) than 15w-40.

Is there any good reason why I should choose a 15w-40 over a 10w-40? So far I haven't.

Thanks.


Yeah, I saw the graph showing the recommended grades in your other thread Critic. You often see a similar thing in older guides where they sometimes show 10w30 being suitable for far higher temperatures compared to 5W30. The simple fact is that for modern good quality "stay in grade" oils there is no reason why 10W30 would be better at high temperatures (compared to 5W30) and similarly with 10W40 versus 15W40.
 
Originally Posted By: fdcg27
For an old BMW, M1 15W-50 is the perfect oil.
I ran a 15W-40 HDEO the summer before this past (Castrol Tection Extra) for 6K, and had noticeable leaks, consumption of a quart every 1500 miles, and 29 mpg. With M1 15W-50, I had no noticeable leaks, consumption of a quart every 2200 miles, and 31 mpg.

This is surprisingly good news indeed... moving up in weight from 15W-40 to 15W-50 and achieving a 7% improved fuel economy !
Are you saying that you switched to a thicker oil and gained fuel economy, or did other driving conditions also change?

regards,
 
Originally Posted By: fdcg27
Critic, trust me on this.
For an old BMW, M1 15W-50 is the perfect oil.
I ran it for 6K last summer.
Consumption was really low, and the kind of leaks that leave drops in the driveway or garage never happended, which is not the case with Maxlife 10W-40.
Run M1 15W-50 and change it every 6K or once a year.
In my experience, it is the ideal oil for an old BMW which will have oil leaks and will have oil consumption.
I ran a 15W-40 HDEO the summer before this past (Castrol Tection Extra) for 6K, and had noticeable leaks, consumption of a quart every 1500 miles, and 29 mpg. With M1 15W-50, I had no noticeable leaks, consumption of a quart every 2200 miles, and 31 mpg.
Your car, your choice.


Wonder if the thicker oil gave your engine better compression?
 
I, too, drive an older BMW, a 1985 535i with the M30 engine. This engine has 280,000 miles on it! I have used M1 15W-50 in it, however it gets cold here in Ohio. Based on some very good UOAs, I have been continuing to use M1 HM 10W-40. No leaks and low consumption. Great anti-wear package in this oil.

There are those who run Valvoline VR-1 Racing 20W-50 in these engines because they have, in my opinion, an unreasonable fear of cam wear and believe the added ZDDP will help. I am old enough to remember that BMW 2002 owners were similarly wringing their hands over valve seat recession when lead was being removed from gasoline. However, BMW's metallurgy is top notch and the problem never manifested itself, just as it won't now with cams. An acquaintance who has been an independent BMW mechanic for 25 years states he has *never* seen a worn cam in an a properly oiled engine. Meaning the oil pressure was good, and the sprayer bars were functioning properly.

I think the fact there are so many of these '80's BMWs still driving around means the actual oil in the car isn't as important as making sure the oil is not worn out, and that the systems that deliver the oil are functioning.
 
I'm no expert on euro cars, but in a warm climate, I don't think you can go wrong with an inexpensive 15W-40 in that car. It will keep the engine clean, and not shear down much, and won't cost a lot.
 
I dunno, maybe?
Another possibility is that the thicker oil brought lower consumption, which in turn allowed more timing advance, and thus lower fuel consumption.
A third possibility is that M1 15W-50 contains a significant ester component (Mobil isn't telling) which would provide reduced friction.
Also, esters may (I wrote may) degrade fuel octane less, thereby allowing more timing advance.
Anyway, the old thing did very well on M1 15W-50, while fuel consumption was no lower in the first 4K run of Maxlife 10W-40, and the oil leaks, absent with the M1 15W-50, have returned.
 
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