Motor Oil 103, You have a synthetic mind.

Part Three. You have a synthetic mind.

Let us compare mineral and synthetic oils. I will not talk about chemical but rather functional differences. We discussed before how mineral oils are too thick at startup yet too thin when hot. The viscosity was corrected with the hot engine by adding VI improvers.

A 10W-30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 weight oil when hot. It acts more as a 10 weight oil at startup. I remind you that a 10 or 5 or 2 weight oil is still too thick to provide lubrication at startup. They are all too thick at startup. There is currently no engine oil thin enough to operate correctly at startup. They all cause excessive wear at startup. Again, we are discussing the needs of my single hypothetical engine for around town driving.

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
Straight 5...........20.....................4
Straight 2...........15.....................3
Straight 0...........12.....................3 est.

A 10W-30 synthetic oil is based on a 30 weight oil. This is unlike the counterpart mineral oil based on a 10 weight oil. There is no VI improver needed. The oil is already correct for the normal operating temperature of 212 F. It has a thickness of 10 while you drive to work. It will never thin yet has the same long term problem as the mineral based oil. They both thicken with extended age.

Synthetic oils are derived in the laboratory. They are pure, usually nearly clear. I describe mineral based motor oils as a distilled, concentrated product. The impurities need to be removed from the raw petroleum. These oils are therefore less clean and contain many impurities. Again, the problem is really more of theory than practice but the difference does exist.

People repeatedly say that synthetic oils are more stable in a hot engine. I hear that they lubricate better. The answer is yes and no. Oil molecules do not break down, just the additives. Generally, the synthetic oils do not have VI improvers so have less to lose.

There are some properties of synthetic oils that actually result is less wear than with mineral oils. These help increase your gas mileage as well. Due to a reduction of internal friction of the synthetic oil your engine will run a bit cooler. Wear increases as temperature increases, all other things being constant.

A main advantage that the synthetic has over the mineral based oil is the ability to lubricate at startup. Both types of oil have the same specifications at 104 F, 212 F and 302 F. It is the startup viscosity characteristics that separate these oils. Synthetic oils do not thicken as much on cooling. They have better fluidity as the temperature drops.

A synthetic oil that is labeled as 10W-30 is less honey like as a mineral based 10W-30 motor oil at startup. They both have a thickness of 10 at normal operating temperatures. At 75 F the synthetic is not as thick. At 32 F the difference between the two is even greater. At 0 F the mineral oil is useless yet the synthetic works fairly well. Just keep the RPM to a minimum.

At temperatures below zero you will not be able to start your car with mineral oils while the synthetic oils may be used to -40 or - 50 F. Oils are so thick that the normal method of viscosity measurement is not possible. Instead we measure if the oil can even be pumped or poured. Again, we are only discussing a single category of oil, the multigrade 10W-30 API / SAE grade.

I took an except from the web about Mobil 1 oils. They compared a 5W-30 synthetic Mobil 1 oil to a mineral based 10W-30 and a 10W-40 in ice cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30 Mobil 1. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively. Neither of those engines started.

Motor oil becomes permanently thicker with exposure to northerly winter type weather. This is more of a problem to mineral based oils. Waxes form. This is why it is a bad idea to even store a bottle of oil in a cold garage. It goes bad on the garage self just because it is exposed to the cold.

To recap, synthetic oils have similar characteristics as mineral oils at operating temperatures. The synthetic oil will however be less honey - like at startup even though it has the same API / SAE rating. Yet the synthetic 10W-30 weight oil is based on a heavier 30 weight oil while the mineral based 10W-30 oil is based on a thinner 10 weight oil. They are both similar at operating temperatures yet the 30 weight based synthetic is actually less thick at startup and much less honey - like at low temperatures. This is the opposite of what common sense dictates.


This is worth repeating: The synthetic 10W-30 weight oil is based on a heavier 30 weight oil while the mineral based 10W-30 oil is based on a thinner 10 weight oil. They are both similar at operating temperatures yet the 30 weight based synthetic is actually less thick at startup and much less honey - like at low temperatures. This is the opposite of what common sense dictates.

As one can see this is no easy topic. Are you with me?

aehaas

 

“The $64,00 question is does it really matter for the owner who allows the vehicle to warm up properly vs. some one who does not.”

This will be answered several ways later, please be patient. It is a difficult answer.

“Why do the modern cars use such light weight oils?”

Earlier oils were based on type I base oils, then type II and now mineral based oils are based on type II plus. Synthetic oils start at type III base oils. Mobil 1 is mostly type IV (or at least has been) and Red Line is a type V ester based oil. Base oil characteristic have changed for the better and the additives have improved. Many oils are based on mixtures of different base oils as a little type II plus, type III, maybe some type IV and some type V.

Today's 0W-20 oils give better protection than 20W-50 wt. oils of the past in my opinion. It is the total package that makes the oil. And I believe that the thinnest oil that keeps parts separated is the best.

The engines have not changed much, only the oil technology.


aehaas

 

Again, several posted were lost but this is the third time I am putting this in:


“Have heard some guys say that when they go with thinner oil, from a 20W-50 to a lower viscosity, their engine which did not leak with the thicker oil now does leak with thinner oil. As you know, many blame the oil versus the lack of properly maintaining/condition of their engine seals. So if someone switches, as you suggest, a less thick oil and then their engine starts having oil leaks, what should they do?”

I would stick with the thinner oil but try another brand, maybe a “high mileage” oil. These have extra additives to help seal integrity. One oil may leak and other of the same grade may not. It is certainly wrong to just use a thick oil to stop seal leakage. Fix the leak.

To Artvonne - I agree that today's mineral based oils are very good oils. But let me repeat this: A main advantage that the synthetic has over the mineral based oil is the ability to lubricate at startup. Both types of oil have the same specifications at 104 F, 212 F and 302 F. It is the startup viscosity characteristics that separate these oils. Synthetic oils do not thicken as much on cooling. They have better fluidity as the temperature drops.

Most wear occurs during the start up period and this is why I use synthetic oils. I do not need the higher temperatures they can withstand. You will see why later, the answer is another long one. And for me the start up temperature is never below 50 F and usually 70 - 80 F yet I still prefer the less thick synthetic oils in my high performance engines. I still use plain ‘ol Pennzoil in the Expedition with no fear at all.

I put 105,000 miles on a Volvo 760 turbo running 5W-30 Pennzoil. I changed the oil when it started to be visible on the dip stick. This was about 3,000 miles of city driving and 4,000 miles of mostly highway driving. When I traded it in it was as good as new, maybe better. I toed in the front wheels and gave it more negative camber because of the way I drive - sporty. Incidentally, I have of my own wheel alignment equipment.

I predict that in the future we will find that a combination of mineral based oil and synthetic will actually out perform in the average car in average use.

aehaas

 

The SINT series is a synthetic blend, semi-synthetic.

As far as a 0W-40 being thinner than a 10W-40 - this is false. Please re-read 101 - 102 - 103 and 104.

aehaas