Motor Oil 102. It gets more difficult.

Chapter two. It gets more difficult.

We left off discussing that a 0W-30 weight oil is not thinner than a 10W-30 oil. They both have the same thickness at operating temperature. The 0W-30 simply does not get as thick on cooling as the 10W-30. Both are still way to thick to lubricate an engine at startup.

I have heard several people say that Porsche specifically prohibits a 0W-XX engine oil, that it is too thin. Now here is the partial truth I spoke of earlier. We will discuss multigrade oils. Earlier we said that a straight 30 weight oil has a thickness of 10 at the normal operating temperature of your engine. The multigrade oils 0W-30 and 10W-30 also have a thickness of 10 at 212 F.

The difference is at 75 F, your startup temperature in the morning.


Oil type... Thickness at 75 F...Thickness at 212 F

Straight 30...... 250......................10
10W-30............100......................10
0W-30..............40 ......................10

Straight 10........30....................... 6

Now you can see that the difference between the desired thickness your engine requires ( = 10 ) is closest to the 0W-30 oil at startup. It is still too thick for normal operation. But it does not have far to go before it warms up and thins to the correct viscosity. Remember that most engine wear occurs at startup when the oil is too thick to lubricate properly. It cannot flow and therefore cannot lubricate. Most of the thick oil at startup actually goes through the bypass valve back to the engine oil sump and not into your engine oil ways. This is especially true when you really step on that gas pedal. You really need more lubrication and you actually get less.

Note that a straight 10 weight oil is also too thick for your engine at startup. It has a thickness of 30. Yet at operating temperatures it is too thin having a thickness of 6. It needs to be around 10. The oil companies have added viscosity index improvers or VI to oils to solve this dilemma. They take a mineral based oil and add VI improvers so that it does not thin as as much when it gets hotter. Now instead of only having a thickness of 6 when hot it has a thickness of 10, just as we need.

The penalty is the startup thickness also goes up to 100. This is better than being up at 250 as a straight 30 weight oil though. Oil with a startup thickness of 100 that becomes the appropriate thickness of 10 when fully warmed up is called a 10W-30 weight motor oil. This is NOT as thick as a straight 30 weight oil at startup and it is NOT as thin as a straight 10 weight oil at full operating temperature.

The downside of a mineral based multigrade oil is that this VI additive wears out over time and you end up with the original straight 10 weight oil. It will go back to being too thin when hot. It will have a thickness of 6 instead of 10. This may be why Porsche (according to some people) does not want a 0W-30 but rather a 10W-30. If the VI wears out the 0W-30 will ultimately be thinner, a straight 0 weight oil. When the VI is used up in the 10W-30 oil it too is thinner. It goes back to a straight 10 weight oil. They are both still too thick at startup, both of them. The straight 0 weight oil, a 5 weight oil and a 10 weight oil are all too thick at startup.

This is just theory however. With normal oil change intervals the VI improver will not wear out and so the problem does not really exist. In fact, oils do thin a little with use. This is partly from dilution with blow by gasoline and partly from VI improvers being used up. What is more interesting is that with further use motor oils actually thicken and this is much worse than the minimal thinning that may have occurred earlier.

Synthetic oils are a whole different story. There is no VI improver added so there is nothing to wear out. The actual oil molecules never wear out. You could almost use the same oil forever. The problem is that there are other additives and they do get used up. I suppose if there was a good way to keep oil clean you could just add a can of additives every 6 months and just change the filter, never changing the oil.

When the additives wear out in a synthetic oil it still has the same viscosity. It will not thin as a mineral oil. The fear that some say Porsche has that oils thin when the VI runs out is not applicable to these synthetic oils. These oils will always have the correct thickness when hot and will still be too thick at startup as with all oils of all types, regardless of the API / SAE viscosity rating.

Automotive engine manufacturers know these principals of motor oils. They know there is thinning or thickening that will occur. They take these things into account when they write that owners manual. Mineral oil change recommendations will generally include shorter time intervals than those of synthetic oils.

The reality is that motor oils do not need to be changed because they thin with use. It is the eventual thickening that limits the time you may keep oil in your engine. The limit is both time itself (with no motor use) and/or mileage use.

End of part two.

aehaas

 

Excellent info. Thanks.

 

Dr Aehaas,

great reading as always.

question on oil thickening with use.

i agree that modern fuel injected engines run cleaner and contaminate the oils less. this allows for longer oil change intervals and spark plug life.

older multicarb cars THIN their oil out with use, and should have more frequent oil changes. (gasoline in the oil)

** my question is: did the manufactures of older engines with multi carbs actually spec say 20w50 oils BECAUSE they knew the cars thin thier oils out with use ? **


i agree that my 308 could benefit from a 10w40 oil, but it seems i have always had to run a 20w50 oil in all 4 of them to get acceptable pressure when fully warmed up.


**will more modern oils allow one to run a thinner oil in an older mutlicarb car? **

this is assuming regular use up to operating temps and a proper state of tune.



modern cars that control thier fuel use and delivery would benifit from the thin oils and higher operating temps. ( most newer cars run in the 200 -210 degrees F.)

the precision metering of fuel adds better mileage and less oil to spark plug contamination, allowing for the 7500 mile oil change intervals we see in newer cars.


thoughts?

 

Nice work Ali.

 

Oils of the 1970's and 1980's thinned a lot with use. They then thicken a lot. Thin oils still work whereas thick oil cannot, especially when it gets cooler.

Today oils thin minimally and some do not thin at all. It takes 4 - 5 percent fuel dilution to decrease the viscosity into the next lower grade. Fuel dilution causes damage not so much because it thins oil but because of many other things that hurt your oil's operating characteristics.

Oils all still thicken with use however much less than oils of the past. Some oils thicken sooner some take more time.

aehaas

 

That's rather strange, as the factory recommended oil for all Porsche models new & used (possibly excluding the CGT) is Mobil 1 0W-40.

 

So you are saying, that all things being equal, both new and old oils at the same temp, & you don't have more than 4-5% fuel dilution in your old oil, that the used oil is actually thicker in viscosity than the new oil you replaced it with?

From a visual point of veiw that doesn't see right. In all my old cars I'm sure I've got plenty of fuel diluting the oil, but on my new/newer cars visually it still seems that the old oil is markedly thinner in fluidity/viscosity than the new.

I'm not trying to be adversarial, just seeing if I understand your point correctly.

What about pre-lube set-ups? Perhaps an electrical pump which gets oil to the top end or where ever you want it to reduce start up wear. It wouldn't warm the oil, but at least get it to the critical areas more quickly?

Lasty, given the latest installment, your recomendation is..... synthetic?

Thanks

 

A 10W-30 fully synthetic type IV or V based motor oil probably has no viscosity improvers and thus will thin only from fuel dilution. Most other oils will thin some with use but this is not bad. It is probably good.

The Shell Helix Ultra Racing 10W-60 was tested after 1,400 miles of city driving in an Enzo and only had a viscosity of a 10W-40 grade oil. This is in part why I chose to try a more stable 30 wt. oil, the Castrol Syntec European Formula 0W-30.

You have to look at the whole picture. This is the hard part especially with the confusion about oil can labels. Whenever somebody says that they would never use a 0W-30 because it is too thin and instead use a 10W-30, well they clearly know nothing about motor oil. They need to be educated.

aehaas

Other questions will be answered later. Please hold on.

 

No mention of 5-30w? I use Mobil 1 5-30w..... Does that fall between the two?

Great info....... Thanks

 

Ali, for those of us who struggled to pass kindergarten, it is too simple to say that the best commercially available oil is a synthetic with a -0- for the first number and a -30- for the second number?

Dale

 

i understand now. thank you for the reply.

 

The 5W-30 Mobil 1 is a shear stable oil. Use it with confidence but it would be far better to use their 0W-30 Mobil 1 instead. It is also fully shear stable and will not thin.

aehaas

 

Thanks, I thought you might say something like that. I'll have to look for the 0-30w.

 

Firstly; the articles by AEHaas are superb! Please keep them comming.
I have recently rebuilt my 512BBi engine, and have used Mobile 1 0W40. The oil pressures seem fine (note: the gauge in mine reads only about 50% of the true pressure!)..if anything a little high once the gauge error is considered: 6 bar cold (about 120psi actual), 4 bar at 3000 rpm when warm (80 psi actual) and about 1.5 bar at idle, warm (40 psi actual).

I tried to get more 0W40 this morning and it was no longer available...instead they have 0W20.

Should I top up with 0W20?
Should I use 0W20 for the next oil change, or is 20 a little thin for a Boxer engine?
Should I seek out 0W40 from another source (is it still available?)

Shoud it be a priority lowering the oil presures? It is adjustable on the Boxer using shims, and has an extra shim in there at present. I pressume the previous 'owner' shimed so the gauge was correct. It's a relatively simple job to re-shim.

Any advice appreciated.

 

I'd guess you are right Robert, 120psi sounds WAY high to me.....others??

 

A 0W-30 would be the next thing to try.

aehaas

 

ok, how 'bout pre-warming the oil??
Maybe sumpin' as simple as the old cold weather trick of placing a work light on the floor underneath the oil pan, and letting it warm up the oil for 15-30 minutes or so ??

There was some guy in the 90's who advertised in the usual U.S. car mags about a pre-luber gizmo. Looked interesting, but I never go around to buying one. Anyone know if there's something available these days for Fcars ?

Or, hell, get a buddy, push the car down the street a ways in 5th gear. That'll turn a little bit of oil over inside...

 

I carry a quart of oil all the time in the boot to top off when needed. Sometimes it may be of a different brand and viscosity rating than what I have in the engine. What is the negative effect, if any, in topping off 0W-30 with say a 20W-50?

 

For anything above say 30 - 40 F no pre-warming is needed, just go easy after start up. Below freezing it cannot hurt to warm the oil a little, especially if you are one of those who use heavy oils. I like the idea of a light bulb under the pan. That should be enough in the garage.

You can mix oils but it is best to use the same exact oil. Carry an extra jar of the same type.

aehaas