Air cooling and modern oil?

[Xyzzy]

I've been reading about how older air-cooled engines (Porsche 911, 914, etc.) are being run today, safely, with much lower viscosity oils than they were originally designed for.

And those are very old engines that aren't as "tight" as a modern engine that has had 50+ years of improved manufacturing technology applied to it.

So why do modern Harleys still use 20W50 oil?

I am posting this in the car section even though my question is about a motorcycle. Mainly because a Harley doesn't share the engine oil with the clutch, so a car oil will work fine in it. And because I'm hoping "car people" will maybe think a bit out-of-the-box.

Is the use of such a heavy oil because the Harley uses roller bearings instead of plain bearings?

 

[wings&wheels]

I actually don't know how many air-cooled Porsches are being run on much lower viscosity than originally spec'd. In fact, Porsche Classic oil for the air coolers is either 20w-50 or 10w-60 (I use Redline 10w-60). Heck, Stuttgart offers 10/5w-50 for the water coolers up through the 996/986 (Redline 10w-50 in ours). Most folks I know run various top tier oils in Xw-50.

I don't know much about Harley's other than a Buell I had for a short time, but I do know a bit about Porsches and air-cooled aircraft, so in general I'd guess; air cooled motors can run hotter and temperature variances within the motor are greater than liquid cooled motors, have hot spots of less cooling air flow, varying thermal expansion of engine parts based on the temperature variances and I've read somewhere, and it seems reasonable, that rear cylinders on v-twins can run very hot. Thoughts from a very highly trained.....finance guy, so take them for what they are worth.

Others here will know more.


And welcome!

 

[kschachn]

I've been reading about how older air-cooled engines (Porsche 911, 914, etc.) are being run today, safely, with much lower viscosity oils than they were originally designed for.

And those are very old engines that aren't as "tight" as a modern engine that has had 50+ years of improved manufacturing technology applied to it.

So why do modern Harleys still use 20W50 oil?

I am posting this in the car section even though my question is about a motorcycle. Mainly because a Harley doesn't share the engine oil with the clutch, so a car oil will work fine in it. And because I'm hoping "car people" will maybe think a bit out-of-the-box.

Is the use of such a heavy oil because the Harley uses roller bearings instead of plain bearings?

For what technically advantageous reason?

 

[drtyler]

Where have you read such?

In the aircooled 911 world, 20W-50 and synthetic 15W-50 are by far the most common, with 15W-40 as a distant third place. There is little reason to run oils which are thinner, especially given the costs for any type of engine work on them now.

I've been reading about how older air-cooled engines (Porsche 911, 914, etc.) are being run today, safely, with much lower viscosity oils than they were originally designed for.

And those are very old engines that aren't as "tight" as a modern engine that has had 50+ years of improved manufacturing technology applied to it.

So why do modern Harleys still use 20W50 oil?

I am posting this in the car section even though my question is about a motorcycle. Mainly because a Harley doesn't share the engine oil with the clutch, so a car oil will work fine in it. And because I'm hoping "car people" will maybe think a bit out-of-the-box.

Is the use of such a heavy oil because the Harley uses roller bearings instead of plain bearings?

 

[barryh]

I've been reading about how older air-cooled engines (Porsche 911, 914, etc.) are being run today, safely, with much lower viscosity oils than they were originally designed for.

The whole thing about air cooled engines is that in the absence of an oil cooler there is no control of oil temperature so I think it very much depends on the actual running oil temperatures of the application at hand.

My 79 BMW runs it's oil very cool. Given that I've never measured a sump temperature above 85 C I'm quite happy to relax the recommended viscosity of 20W50 to something thinner. But I wouldn't have done that if If the oil had been getting way above 100 C. To be fair BMW themselves relaxed the recommended oil viscosity requirements as the years went by and were eventually happy with XW40 oils at any ambient temperature provided they were synthetic.

The extreme I mentioned in another thread showed a Moto Guzzi with sump oil at 140 deg C. In that case I wouldn't dare move from the recommended 10W60.

 

[BigTimeTA]

Why would anyone want to move to thinner oils in an air-cooled engine?

 

[nate379]

Hardleys are 1940s tech

 

[thastinger]

I primarily run M1 15-50 in my 98 Harley but I have ran M1 Euro 0-40 in it as well as T6 Rotella. I couldn't tell a difference in any of them TBH.

 

[kschachn]

Apparently just another attempt at a big ol’ spam topic.

 

[Xyzzy]

No spam, I think I read the articles wrong, so I'm doing more reading.

 

[alarmguy]

..

So why do modern Harleys still use 20W50 oil?

I am posting this in the car section even though my question is about a motorcycle. Mainly because a Harley doesn't share the engine oil with the clutch, so a car oil will work fine in it. And because I'm hoping "car people" will maybe think a bit out-of-the-box.

Is the use of such a heavy oil because the Harley uses roller bearings instead of plain bearings?

I suspect because Harley oil temperatures can and do get up to 270 degrees if stuck in traffic on hot days. Heck running on the interstate at 80 to 85 MPH my 2014 Road King will run no less than 245f and top out at 257f
Harley describes normal as 230 and that does happen in normal day to day travel. But traffic and interstate on 90+ degree days, no.

Harley engines spray oil on the bottom of the pistons so the more RPM the more oil being sprayed cooling the pistons that get really hot under load and high speeds. An example of this is once I get off the interstate to normal 55 and under speeds the oil cools down 10 degrees within minutes.