Why 20W-50

[Vintage911Racer]

Why are most High performance motor oils 20W-50?

What is the difference (technically) between a 20W-50 and a 10W-30?

I know there has been a ton of talk about motor oils here. But I have just broken in my new race motor using Catrol GTX 10W-30 non synthetic. My mechanic says I can now switch to Mobil 1 synthetic if I want to. He says the 20W-50 is to thick. He recommends using 10W-30 as my racing oil. He even said he has no problems with me using a Zero weight Oil in colder conditions.

What is thought to be the best oil synthetic or non for racing purposes that will not robb me of HP but will still provide great protection.

Thanks for your help

[Vintage911Racer]

Come on guys. Some one must have some input.

[s_wilwerding]

The general idea behind multi-weight oil is that, as the temperature decreases, the oil becomes thinner, making it easier to circulate. As temperatures increase, the oil becomes thicker, which protects the engine.

I always used 20W50 in my 911 because:

A. I never drove it when it was below 50 degrees
B. Air cooled engines tend to run hotter than water-cooled engines, and need a commensurately heavier oil
C. When I drove my 911, I drove it hard, which meant sustained high temperatures. This is especially true of race engines, that never run cold other than very brief periods

Since all of these things are true of Porsche race engines, it's generally a good idea to run a heavier oil.

Just my $.02

[Chuck Moreland]

No way I'd run 10W-30 in a race engine. You need the viscosity to protect at higher temperatures. Even if you have plenty of oil cooling, remember that your oil temp guage shows the average temperature. There are localized parts of the engine that are much hotter; heads, pistons.

I have tech topic on my web site that explains engine life vs temperature and viscosity.

Have look at this graph to see how different weight oils lose viscosity at temperature:

[MotoSook]

At a party this past weekend, a local who works for Mobil handed me a flyer for Mobil's new Racing Formula 0W30, "good for up to 400F." And they even put "Factory Fill" on the flyer for a number of cars, including Porsche.

It might not coke until 400F, but I wondered what the viscosity number is at 400F or 300F. The "factory fill" list is likely today's car, not the aircooled cars we drive. So yes, Porsche puts that in the cars rolling of the assembly line today, but those are water cooled cars! Do those water cooled cars ever see 250F? Not unless something is wrong...

Our aircooled heads get HOT!

The 50 in the 20W50 is what helps at high temps...basically, I read somewhere, the 20 in the 20W50 makes your oil act like a 20 wieght oil when cold and the 50 makes you oil act like a 50 when hot.


If you are running in cool climates, an 0W30 is probably fine, but if you live in AZ and it's summer out, I would trust the what has worked for us for so long, the 20W50....or if you really must use a synthetic, use a 10W40.

A 20W50 dino oil is just fine...unless you don't plan to change your oil as often as you should...then go synthetic.

You can get tech data sheets for just about any oil you wanna use. Read it and determine for yourself what you want to use.

[brawlins]

On a side note -
You mentioned moving to synthetic oil.
I have a 82SC and my car leaked oil terribly after I switched to Mobil 1 synthetic after an engine rebuild. I had to do two oil changes to 20w50 to finally get the leaks to stop.
I understand the seals on some of the older cars can not handle synthetic. I can testify to that.
- Bill

[filou]

Technically speaking 20W50 have the thickest oil fluidity. It is recommend to "used" engines because of the weight of oil create a better seal around pistons, rings etc..... When it comes to high revs engines like a racing engines for example, i would not put a more than necessary oil weight in the engines because at that stage of operation the oil might get "in the way" due to his extra thickness.
I still wouldn't put synthetic oil because i don't know enough of their impact on older, classic engines. You have to understand that a thinner oil exchange heat from engine at a lower operating temperature.
there are factors that should come into the equation : where and when you are going to use that engine and push it to the limits.
what oil does ??? : provide lubrication and in the same time takes away heat from engine. I noticed that it takes longer for heavier oil to get to ideal operating temperatures. I think you need to analyse the situation in which you are going to use the engine and only then you can decide which oil is more appropriate and suitable.
i think temperature is a big factor.
Truly, Filou.

[azasadny]

I use Castrol 20w50 for the same reasons s_wilwerding listed.

[Vintage911Racer]

This motor so far has not seen over 205 degrees. That is not hot by an means. I run this motor to 8K for 30 minute races. So it cools just fine.

Also my mechanic says not to worry about the leaking issue with synthetics. He told me this engine will not leak. My fathers motor has run on Mobil 1 synthetic 15-50 for the past 3 years. NO Leaks.

So if I just put new Castrol GTX 10W-30 in my car this weekend (since I adjusted my vlaves) Do suggest that I drain it and run a 20W-50 oil or do you think I can leave the 10W-30 in it. My next race is in 2 weeks in Vegas.

[aigel]

I'd go with synthetic on a freshly rebuilt engine. Leaking should not be an issue. Generally people seem to agree that the film will break down quicker on a non synthetic oil, especially at the top piston ring where things get extremely hot on the air cooled flat six!

There is many factors going into the use of enigne oil. One is the tolerances / bearing clearances that were built into the engine. Generally, racing engines are built with LARGER tolerances, as far as I understand, mainly to allow more oil to move over the bearings. This cools the bearing surfaces better. Racing engines therefore often have high volume oil pumps and use thicker viscosity oil.

And this is where your mechanic comes in: If he built the engine and he knows what specs he put on the bearing clearances etc. I'd go with his recommendation! Don't listen to anybody else, because those folks have not built the engine. If someone builds flat sixes for their living, it isn't like Charlie down at the autoparts store gave you the recommendation, because that's what he uses in his Chevy 350.

If the enigne builder thinks that the engine can take the thinner oil, he probably dialed things in tight. If you use too thick an oil, you may have trouble having a good film on the bearings because the clearance is too small and the pump can't 'squeeze' the oil in there fast enough. Your bearings furthest away from the oil pump may starve also, if the oil is too thick for your clearances.

So, to summarize, I think in a new engine, synthetic is the way to go. It will have many of the aspects the 20-50 dyno juice gets you (film break down at high temp isn't an issue). Go with the viscosity your engine builder recommends, since he knows what the bearing clearances are.

Good Luck!

George

[aigel]

I just read you last post. Do NOT go with dyno 10-30. Go with synthetic. It will break down much less at high temp. I'd drain the 10-30 castrol (which is non synthetic, right?) and fill it with the sythetic your engine builder recommended.

George

[Vintage911Racer]

George, That makes sense to me.

THis is his lively hood. I trust him. Not only does he build most of the porsche engines racing in my group, he himself is one of them. He brings about 7-10 porsche to all our races, maintains them and races himself. So I do beleive going with his recommendations would be smart. But I have heard so many different ideas about this, I just thought I would ask.

Thanks

[Randy Webb]

Only part of the issue is the viscosity per se. Muti-wt. oils contain big "springy" molecules to provide a range of viscosities. They contract or expand as temperature changes to provide the oil's ability to operate at the different temperatures. This is great except for one thing -- itis these molecules that are the most susceptible to break down ('cokin') at high temps. Synthetics need less of such molecules to provide lubricity at a range of temp.s, hence will be better and esp. so in a hot air cooled engine.

But I use dino oils in my cars - they are street cars, and the dino oils work just fine for many hundreds of thousands of miles -- look at how long PAgs engines lasted using oils of 20 years ago - the dino oils are even better now. For that last bit of protection, for a hot climate, for a race engine, strongly consider synthetic oils.

[Chuck Moreland]

Originally posted by Vintage911Racer
This motor so far has not seen over 205 degrees. That is not hot by an means. I run this motor to 8K for 30 minute races. So it cools just fine.

How hot is the oil lubricating your wrist pins? Valve guides, Cams?

205 is plenty cool, but it is the average termperature measured at one point on the engine. It is not the hottest termperature your oil experiences.

If your motive is to reduce HP loss due to thick oil, use a 15-50 synthetic or one of the new 10W-50 synths. These will flow easier than dino 20W-50.

[911pcars]

I think this has to do with oil film strength. Historically, with dino oils, increased viscosity counteracted the natural tendency for oil to lose viscosity with increased temperture. As viscosity decreases, so does the strength of the oil film, then metal-to-metal contact becomes a reality.

With the advent of synthetic oils, film strength is no longer a sole function of increased viscosity (and associated additives). In addition, excessive viscosity increases frictional loss in an engine. I wonder what the Williiams F1 engines use at 18,000 rpm? 20-50? Don't know.

As long as the lubricant provides adequate film strength and safety margin for the operating conditions, a lower VI should be fine. Synthetics provide the safety margin with lower viscosity. If you use dino-based oil, stick with 20-50.

The above is based on mild to warm ambient temperatures. If your location is at 30 or below, I suggest using synthetic or a lower number multi-viscosity dino oil.

Sherwood

[Early_S_Man]

Why 20W-50

Because SAE 0W-60 isn't generally available, yet! Europe has had it for a couple of years, now ...

[rhk109]

I've heard that the farther the span between the cold and hot rating the more additives, and therefore less lubrication, the oil provides. I 've been warned away from anything with a span greater than 30. 0W60 would be a no-no. Can anyone confirm or deny this?

[MuffinMan]

I've heard the same thing for dino (conventional) oil, but it is not as true with the synthetics.

[Amac]

Thicker oil = better compression, better oil pressure, better
cooling, better protection.
In the winter I run 20w-50, in summer 50w.
My choice for 50w is valvoline racing oil,
for 20w-50, castrol GTX.
I've run synthetic in the past, had lower oil pressure
and trouble with oil leaks.

[Lothar]

Brawlins,

I believe the problem with the older cars is the "lack of seals". Older engines and old seals will not retain oil that has smaller molecules to seep past compromised areas or were mating surfaces have warped.

That said, I have a recently rebuilt 3.0L SC motor that does not leak a dropof its Mobil 1 except for a bad o ring at the oil line to the right side chain tensioner.

Question: Should a motor freshly rebuilt from top to bottom be as tight as new? Is there a level of machine work that could be overlooked or could a corner be cut that would open the possibility of oil leaks post rebuild?