Thick oil, thin oil piston wear

[Gokhan]

With the European car makers recommending thicker oil, it's partly because of their culture and partly because of possible extreme-load autobahn use (driving at near full engine loads).

With the heavy-duty diesel engines, soot particles are abrasive and need a thicker oil film so that they are smaller than the thickness of the oil film -- otherwise, they would rub into sliding metal parts and wear them out quickly. Gasoline engines don't have this problem, as the insoluble particles in the oil are less harmful.

Thin vs. thick oil is certainly a compromise and not black-and-white. I think the rule of thumb is to use the thinnest oil that doesn't increase the wear significantly. As long as the wear is OK, you will benefit from the better flow, cooler oil temperature, smaller oil pressure, better fuel economy, better cold-engine performance, etc. of thinner oil. At certain thinness, the wear will start to increase and that thinness point will depend on the engine type, engine construction, and even the oil type, as well as the driving conditions.

 

[turtlevette]

Originally Posted By: Gokhan
With the European car makers recommending thicker oil, it's partly because of their culture and partly because of possible extreme-load autobahn use (driving at near full engine loads).

With the heavy-duty diesel engines, soot particles are abrasive and need a thicker oil film so that they are smaller than the thickness of the oil film -- otherwise, they would rub into sliding metal parts and wear them out quickly. Gasoline engines don't have this problem, as the insoluble particles in the oil are less harmful.

Thin vs. thick oil is certainly a compromise and not black-and-white. I think the rule of thumb is to use the thinnest oil that doesn't increase the wear significantly. As long as the wear is OK, you will benefit from the better flow, cooler oil temperature, smaller oil pressure, better fuel economy, better cold-engine performance, etc. of thinner oil. At certain thinness, the wear will start to increase and that thinness point will depend on the engine type, engine construction, and even the oil type, as well as the driving conditions.


The real answer is to use an appropriate sized oil cooler. You don't want 300deg oil trying to cool the pistons even if it is at the proper viscosity by using a 50 or 60 wt oil. Oil is a very important piece of the cooling system. We forget that.

I think they will come up with an answer for thinner oils for diesels too. They should not be exempt from efficiency mandates.

How many people on BITOG run on a road course. I do. There may be a half dozen others. Everyone else driving a car on the street should stick to 0W-20 oil. And the real answer for racing is an oil cooler, not heavier oil.

I don't mean to argue with you. I find your posts to be intelligent, well reasoned and free from political ranting.

 

[jrustles]

Originally Posted By: turtlevette
And the real answer for racing is an oil cooler, not heavier oil.




This is true, only when considering bulk oil temperature control. One must consider the local temperature rise that the oil is subjected to throughout it's cycle. A few instances would be the turbo-shaft, ring belt, pin area, including beneath the crown and of course the bearing.

Controlling your bulk oil temperature only controls the temperature of the oil going into these areas, and viscosity of the temperature controlled bulk oil must be considered.

 

[turtlevette]

Originally Posted By: jrustles
This is true, only when considering bulk oil temperature control. One must consider the local temperature rise that the oil is subjected to throughout it's cycle. A few instances would be the turbo-shaft, ring belt, pin area, including beneath the crown and of course the bearing.

Controlling your bulk oil temperature only controls the temperature of the oil going into these areas, and viscosity of the temperature controlled bulk oil must be considered.


But isn't oil coking the real issue, not viscosity. How does a heavier viscosity in of itself help that issue?

And if you're starting at a 195 deg point with a big ole oil cooler, you're not going to see as large local temps say 80 deg rise for example. That puts you at 275.

Running 60wt oil with no cooler at 300deg results in a local temp rise that puts the oil outside of its design range. In the example it would be 380.

Who says thicker oil resists coking any better than thin?

 

[Iketh]

Originally Posted By: turtlevette
I think they will come up with an answer for thinner oils for diesels too. They should not be exempt from efficiency mandates.


They are exempt because oil efficiency fades to non-existence above ~250tq.

It barely affects 200hp applications. You can meassure a difference in your prius though going from 0w-20 to 20w-50.

 

[jrustles]

Originally Posted By: turtlevette


But isn't oil coking the real issue, not viscosity. How does a heavier viscosity in of itself help that issue?

And if you're starting at a 195 deg point with a big ole oil cooler, you're not going to see as large local temps say 80 deg rise for example. That puts you at 275.

Running 60wt oil with no cooler at 300deg results in a local temp rise that puts the oil outside of its design range. In the example it would be 380.

Who says thicker oil resists coking any better than thin?






coking is one issue, yes. viscosity breakdown is another issue. an oil can break down/temp. shear well beyond a suitable viscosity without coking, and can repeat this cycle many times still without coking.

 

[edhackett]

Originally Posted By: turtlevette


But isn't oil coking the real issue, not viscosity. How does a heavier viscosity in of itself help that issue?

Who says thicker oil resists coking any better than thin?


All things being equal, thicker oil is less volatile, therefore more resistant to being "burned" off an leaving deposits. Here's an example that ties nicely into the 'Advantages of a straight weight oil' thread. Scroll to the 4th page. GF-5, 5W-20 through 10w30 maximum is 30 mg. 0W-20 does not have a limit.

TEOST

Careful blending of base oils and additives can result in good performance of multi-grades on the TEOST test. Straight weights will likely always be higher in deposit formation as VI improvers are known to cause deposits. The other additives needed in multi-grade oils likely contribute, along with the thinner base stocks used. Mobil has said that 0W-20 oils don't perform as well in deposit formation tests as heavier grades.

Ed

 

[OVERKILL]

Originally Posted By: turtlevette


The real answer is to use an appropriate sized oil cooler. You don't want 300deg oil trying to cool the pistons even if it is at the proper viscosity by using a 50 or 60 wt oil. Oil is a very important piece of the cooling system. We forget that.


Certainly. But many high performance applications still spec heavy oil AND have an oil cooler. My M5 has an 8L sump and a factory oil cooler. The Ford examples I cited earlier that spec 5w-50 also all have oil coolers, as does the GT-R and the BMW (and F-cars) cars that spec 10w-60

 

[turtlevette]

Originally Posted By: OVERKILL

Certainly. But many high performance applications still spec heavy oil AND have an oil cooler. My M5 has an 8L sump and a factory oil cooler. The Ford examples I cited earlier that spec 5w-50 also all have oil coolers, as does the GT-R and the BMW (and F-cars) cars that spec 10w-60

And yet many "regular" Mustang GT's are going to end up on a track. Many of the "track pack" cars are going to be collector items and will never see a track.

From a technical standpoint, why use a heavy oil if oil temps can be controlled?

 

[OVERKILL]

Originally Posted By: turtlevette
Originally Posted By: OVERKILL

Certainly. But many high performance applications still spec heavy oil AND have an oil cooler. My M5 has an 8L sump and a factory oil cooler. The Ford examples I cited earlier that spec 5w-50 also all have oil coolers, as does the GT-R and the BMW (and F-cars) cars that spec 10w-60

And yet many "regular" Mustang GT's are going to end up on a track. Many of the "track pack" cars are going to be collector items and will never see a track.

From a technical standpoint, why use a heavy oil if oil temps can be controlled?





Ford's solution to that was a thermal castration mechanism to cut engine power. The "regular" GT's that get tracked may, as SteveSRT8 observed at Homestead, go into thermal protection mode. The 5w-50 spec'd cars are assumed to have a higher thermal ceiling.

In the case of the cars that spec the heavier oil: You'd want to use it to retain warranty, as noted in the owners manual. I'm sure on the street and even drag racing you could get away with using the 5w-20 but obviously Ford didn't find any compelling reason to state that in the OM and they didn't shorten the warranty, so one must also assume that Ford didn't observe any premature wear with the heavier lubricant that would potentially cause issues for them down the road either.

 

[KrisZ]

Originally Posted By: turtlevette

From a technical standpoint, why use a heavy oil if oil temps can be controlled?



Because lighter oils do not have the same film strength as well as HT/HS viscosity as the heavier grade oil. So, to accommodate for this, the bearing surface area has to be larger. There are technical limitations to the size of the main bearings depending on engine configuration, displacement and the power density (HP/L).

That is why big rigs can use only one or two grades heavier oils even though they can pull loads 10/20 times higher than the average car or light duty truck. The reason is that their bearings are huge and the load can be spread over a much larger area.

I'm not sure where you got the idea that Xw20 oils have the same film strength as heavier oils, but it is not true.

 

[il_signore97]

Originally Posted By: turtlevette


From a technical standpoint, why use a heavy oil if oil temps can be controlled?




I believe there are many technical reasons for using a specific viscosity of oil, while also (and independently) controlling oil temperature as well. Both are important factors in engine operation, but are not necessarily related in all respects. Yes, a colder 20 grade oil can have the same kinematic viscosity as a hotter 30 grade oil for example, but that does not make them equal in every situation.

Engine design, bearing design, lubrication requirements, vehicle use, oil film strength, longevity of intended OCI, particulate loading, etc, etc, all play very important factors in determining optimal oil viscosity.

My Benz calls for an MB approved 229.5 oil, which will be any 0W40, 5W40, or European-style 0/5W30 with an HTHS of 3.5 cP or greater. I normally use 0W40, and for 20,000 km OCI's (12,500 miles) as per MB. I do not anticipate any oil related issues for the life of the car. It currently has 100,000 km on it now, and literally does not burn a drop of oil, not that I can tell anyway. The level on the dipstick 20,000 km later is still in the same spot.

My car takes 8.5 qts of oil and is equipped with a very large oil-to-coolant heat exchanger. The exchanger both cools the oil once the car is warmed up, but also warms the oil when it is cold. My oil temp is generally in the vicinity of coolant temp, and does not deviate very much, even when pushed hard for a while. But I assure you, even though temp is well controlled, I won't be running any 20 grade oils in this engine, nor any North American style 30 grade oils (HTHS of ~3.0 cP). There are very good reasons why Benz calls for the oil they do, and the modern, high tech 0W40 works well in both cold and hot conditions, under high load, or any conditions that can be thrown at the vehicle. Definitely not an old man's oil

 

[Shannow]

Originally Posted By: Iketh
Originally Posted By: turtlevette
I think they will come up with an answer for thinner oils for diesels too. They should not be exempt from efficiency mandates.


They are exempt because oil efficiency fades to non-existence above ~250tq.

It barely affects 200hp applications.


Turtlevette wrote operating procedures for multi thousand HP diesel engines in nuclear power stations. Engines that were pre-warmed, had complicated oil and water cooling systesm, and were required to run full "throttle" within tens of seconds of a start.

He knows all the above, he's just testing us.

 

[SteveSRT8]

People on this site have always been way too tight about oil temps.

At Homestead I was running 290-300 degrees and got a bit worried. I emailed Mobil and was told that 300 degrees would not hurt the oil.

2 completely separate OA confirmed there was no issues. The engine is now 9 years old and still runs like a screaming banshee.

Mfgrs know this and have no worries. Modern oils have no problems with high temps.

 

[Clevy]

Originally Posted By: Shannow
Originally Posted By: Iketh
Originally Posted By: turtlevette
I think they will come up with an answer for thinner oils for diesels too. They should not be exempt from efficiency mandates.


They are exempt because oil efficiency fades to non-existence above ~250tq.

It barely affects 200hp applications.


Turtlevette wrote operating procedures for multi thousand HP diesel engines in nuclear power stations. Engines that were pre-warmed, had complicated oil and water cooling systesm, and were required to run full "throttle" within tens of seconds of a start.

He knows all the above, he's just testing us.




Hehehe.

 

[turtlevette]

Originally Posted By: SteveSRT8
People on this site have always been way too tight about oil temps.

At Homestead I was running 290-300 degrees and got a bit worried. I emailed Mobil and was told that 300 degrees would not hurt the oil.

2 completely separate OA confirmed there was no issues. The engine is now 9 years old and still runs like a screaming banshee.

Mfgrs know this and have no worries. Modern oils have no problems with high temps.


I agree. The amount of time you're at 300deg is just minutes at a time. Why put a 40-60 wt oil in just for that contingency.

 

[Shannow]

Because in that couple of minutes, metal might meet metal and wreck something ???

 

[demarpaint]

Originally Posted By: Shannow
Because in that couple of minutes, metal might meet metal and wreck something ???

That's what I was thinking and a 30 grade might be just a bit better than a 20 grade for that couple of minutes.

 

[turtlevette]

Here's a really nice study on thick vs thin.

http://www.bobistheoilguy.com/forums/ubb...vel#Post2349276

 

[OVERKILL]

Originally Posted By: turtlevette
Here's a really nice study on thick vs thin.

http://www.bobistheoilguy.com/forums/ubb...vel#Post2349276


Without actual tear-downs with measurements that data doesn't mean much.