Lets talk about Oil for air cooled engines.

So someone on the Corvair Owners Group on Facebook asked a simple question about what motor oil to use in he '63 Spyder (turbo) that he's bringing back from the dead. He mentioned that he lived in Florida so the Summers can get pretty hot sometimes averaging about 95 degrees, but in the winter it can get down to the 50s.

This sparked a huge debate. I, along with several others have suggested to him that 15w40 is an ideal weight for the hotter climate areas of the US. I threw in, that if he's worried about the heavier weight oil for start up, that 10w40 is acceptable. I also suggested that he doesn't have to use the same weight through the year; 15w40 in the summer and 10w40 in the winter would be an idea as well. A couple folks who run the Forward Control trucks suggested 20w50, but those guys were from the Southwest, so I'd understand it with those temperatures.

However, there are several people who are saying that the 15w40 is too high of a weight at start up and it will wear your engine faster. I've rebuilt several Corvair engines and all of them are still running just fine on 10w40 and 15w40.

So what would you guys say is an ideal oil for an Air Cooled engine?

Brand is always a personal preference, but I'm always up to those as a suggestion as well. I've always run Rotella T 15w40 in my rebuilds, my dad has always run Royal Purple 10w40 in his rebuilds, and I know a couple guys running Brad Penn 10w40 and 15w40.

The first number is the cold viscosity, so for Florida it's essentially unimportant as it's not going to get super cold there. The 40 sounds good, but I am not sure why you were thinking 15W for the first part, can you explain?

In reply to tuna55:

Because it's what I've used. I feel like a 15 weight oil is a good idea in an 60 year old engine for start up. I've never had an issue with it, that's why I'm not understanding why people are saying it would cause a faster wear on an engine. Maybe on a modern DOHC motor from the last 15 years, but not in an older engine.

In all my VWs I've used Valvoline VR1 20w50 or a straight 30w and never had a problem.

I run 20w50 in the built British Leyland 1275 A engine in my Sprite. It's fully old-tech and has a fair amount of compression and valve lift, and only get started a few times over the course of the winter, generally at the end of a long day when the garage heater has been running. Of course it's water cooled, but the level of engine tech is quite primitive, and under hard use it can get some pretty elevated oil temps.

I rode air-cooled BMW 900 and 1000cc boxer motorcycles many years. 20-50 was considered the standard oil for the 70's bikes, the later 80's bikes with plated bores ran 10-50. In Washington DC summer weather it was water consistency at best when much sitting in traffic was done.

80's Carrera factory recommendations.

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Based on my HD experience, I was going to suggest 20W50, and I see that's what the P-Car suggests also.

I'd be thinking Rotella T6 5w40 or maybe M1 15w50 for really severe service in very hot weather, definitely heavy duty/diesel rated oils or full synthetics in any event to better deal with the heat.

A 15w40 will be fine cold starting in 50* weather, in 1963 that car probably got straight 30 goo in it and it worked fine.

I used to run 20-50 in my Nortons. Due to the loss of Zinc in newer motor oils, I now run Diesel oil in air cooled motorcycles, namely Shell Rotella usually. I'm running it in my water cooled Vanagons too, and my other VWs where 10-40 was recommended by the manufacturer.

SyntheticBlinkerFluid wrote: In reply to tuna55: Because it's what I've used. I feel like a 15 weight oil is a good idea in an 60 year old engine for start up. I've never had an issue with it, that's why I'm not understanding why people are saying it would cause a faster wear on an engine. Maybe on a modern DOHC motor from the last 15 years, but not in an older engine.

Why do you feel that 15 or 20 or whatever would be superior to 10 for the cold viscosity? If I am right, 10W is what Chevrolet recommended. Why would you deviate from that? What are you trying to achieve?

Depends on whether you are using US spec or Euro spec oil. US and Japanese oil specifications are tested by cold start characteristics, Euro spec oil bases specs on high load, high heat characteristics.

So a Euro and a US 15w-40 could be completely different.

tuna55 wrote:

SyntheticBlinkerFluid wrote: In reply to tuna55: Because it's what I've used. I feel like a 15 weight oil is a good idea in an 60 year old engine for start up. I've never had an issue with it, that's why I'm not understanding why people are saying it would cause a faster wear on an engine. Maybe on a modern DOHC motor from the last 15 years, but not in an older engine.

Why do you feel that 15 or 20 or whatever would be superior to 10 for the cold viscosity? If I am right, 10W is what Chevrolet recommended. Why would you deviate from that? What are you trying to achieve?

Back in the 60's there wasn't Multi-Viscosity oil. It was just SAE 30,40,50 etc.

To my understanding with the way oil breaks down, your winter weight is going to break down faster than your service duty weight. In an Air Cooled engine where the oil helps cool an engine, the oil has a faster rate of break down than a water cooled engine does. I would want a heavier weight of oil that would have a slower rate of break down than a standard oil like a 10w.

Therefore I would want something like 15w or 20w oil for an air cooled engine. By looking at some of the responses here, I'm not the only one that feels that those weights are better for air cooled engines.

I have to say that 15W-40 is a good weight for use in Florida year round on an "old school" engine, air cooled or water cooled.

IMO most of the switch to "0" weight oils is driven by the search for MPG's by the OEMs. Yes better metallurgy, design, and chemistry do allow these "thin" oils to protect these engines from wear but I don't believe that a 10W-30 is worse then a 0W-30 for any of this except for start up oil flow and really only at temps below zero degrees.

SyntheticBlinkerFluid wrote:

tuna55 wrote:

SyntheticBlinkerFluid wrote: In reply to tuna55: Because it's what I've used. I feel like a 15 weight oil is a good idea in an 60 year old engine for start up. I've never had an issue with it, that's why I'm not understanding why people are saying it would cause a faster wear on an engine. Maybe on a modern DOHC motor from the last 15 years, but not in an older engine.

Why do you feel that 15 or 20 or whatever would be superior to 10 for the cold viscosity? If I am right, 10W is what Chevrolet recommended. Why would you deviate from that? What are you trying to achieve?

Back in the 60's there wasn't Multi-Viscosity oil. It was just SAE 30,40,50 etc. To my understanding with the way oil breaks down, your winter weight is going to break down faster than your service duty weight. In an Air Cooled engine where the oil helps cool an engine, the oil has a faster rate of break down than a water cooled engine does. I would want a heavier weight of oil that would have a slower rate of break down than a standard oil like a 10w. Therefore I would want something like 15w or 20w oil for an air cooled engine. By looking at some of the responses here, I'm not the only one that feels that those weights are better for air cooled engines.

But the cold weight is only really for startup, so the only proof of your theory is that a 10W based oil would have lower oil pressure and/or slower pressure build up at startup. I really doubt this would happen. The 20W is going to be slower to pump through the engine at startup.

In reality, it probably doesn't matter, but I'd want data first.

In reply to SyntheticBlinkerFluid:

You aren't going to see much shearing/break down of a modern HDEO (especially a full synthetic like Rotella T6 5w40) on a conservative interval in an engine like this. A $14+shipping UOA (napa P/N FIL 4077) will confirm this. Only benefit I can think of that a heavier cold rating would provide is it will drain out of bearings in a infrequently used engine more slowly, maybe. OTOH, the thinner oil will pump up quicker from a cold start.

850Combat wrote: I used to run 20-50 in my Nortons. Due to the loss of Zinc in newer motor oils, I now run Diesel oil in air cooled motorcycles, namely Shell Rotella usually. I'm running it in my water cooled Vanagons too, and my other VWs where 10-40 was recommended by the manufacturer.

Just small FYI the zinc in Diesel oil in now lower too. However motorcycle and "racing" oils still have high levels. Pen grade 1 and Valvoline VR1 both are high zinc and great for air cooled motors

tuna55 wrote:

SyntheticBlinkerFluid wrote:

tuna55 wrote:

SyntheticBlinkerFluid wrote: In reply to tuna55: Because it's what I've used. I feel like a 15 weight oil is a good idea in an 60 year old engine for start up. I've never had an issue with it, that's why I'm not understanding why people are saying it would cause a faster wear on an engine. Maybe on a modern DOHC motor from the last 15 years, but not in an older engine.

Why do you feel that 15 or 20 or whatever would be superior to 10 for the cold viscosity? If I am right, 10W is what Chevrolet recommended. Why would you deviate from that? What are you trying to achieve?

Back in the 60's there wasn't Multi-Viscosity oil. It was just SAE 30,40,50 etc. To my understanding with the way oil breaks down, your winter weight is going to break down faster than your service duty weight. In an Air Cooled engine where the oil helps cool an engine, the oil has a faster rate of break down than a water cooled engine does. I would want a heavier weight of oil that would have a slower rate of break down than a standard oil like a 10w. Therefore I would want something like 15w or 20w oil for an air cooled engine. By looking at some of the responses here, I'm not the only one that feels that those weights are better for air cooled engines.

But the cold weight is only really for startup, so the only proof of your theory is that a 10W based oil would have lower oil pressure and/or slower pressure build up at startup. I really doubt this would happen. The 20W is going to be slower to pump through the engine at startup. In reality, it probably doesn't matter, but I'd want data first.

What I'm trying to say is that 10w is going to thin out faster over time than a 15w or 20w in an air cooled engine. While yes the thinner oil is great to have there for the sump to pump quickly, I wouldn't mind having the thicker oil still on the bearings and in the galleys at start up after it's been sitting for a few days.

I would still plan to change the oil every 3000 miles or 3 months, so yes it probably doesn't matter in the long run.

Honestly, I'm just going from experience. It's what's worked for me so far and I don't plan on changing it.

I understand what you're trying to get at, but I like having the thicker oil for the air cooled stuff.

44Dwarf wrote:

850Combat wrote: I used to run 20-50 in my Nortons. Due to the loss of Zinc in newer motor oils, I now run Diesel oil in air cooled motorcycles, namely Shell Rotella usually. I'm running it in my water cooled Vanagons too, and my other VWs where 10-40 was recommended by the manufacturer.

Just small FYI the zinc in Diesel oil in now lower too. However motorcycle and "racing" oils still have high levels. Pen grade 1 and Valvoline VR1 both are high zinc and great for air cooled motors

Current diesel oil has about the same zinc content as passenger car oil of the late 60s did after it was raised to protect higher spring pressure flat tappet cam apps. Past 800-900 PPM it's mostly just a cheap antioxidant.

I was thinking 1200-1300ppm was the sweet spot, but I haven't been on BITOG in a couple of years.