What is the quarts "range" on the dipstick on these trucks?

[KMeloney]

So if we take the Engine Labs article that StephenPT linked about oil viscosity and make the following observations and assumptions and then we back into the answer a bit.

For the main bearing oil clearance for an aluminum block and the recommended oil viscosity.

1. Assume we do not know or care about the L87 main bearing oil clearances.

2. We use the reference point in the chart for an aluminum block at the mid oil temperature range (160-220F) and find where 0W20 oil is recommended. This is for main bearing clearances is in the range of 0.0012-0.0017 inches.

3. Then we look at the same bearing clearance row, but look at the oil viscosity recommendaton for the next oil temperature range of over 220F oil temperature, we see the recommended oil viscosity rating is 5W30 or 10W30.

Then we do the same thing for the steel connecting rods.

1. Assume we do not know or care about the L87 rod bearing oil clearances.

2. We use the refernece point in the chart for steel connecting rods at the mid oil temperature range (160F-220F) and find where 0W20 oil is recommended. This is for rod bearing clearances is in the range of 0.0016-0.0021 inches.

3. Then we look at the same bearing clearance row, but look at the oil viscosity recommendation for the next oil temperature range over 220F oil temperature, we see the recommended oil viscostiy rating is 5W30 or 10W30.

My initial high oil temperature log indicated a 226F max with no real load and cooler ambient tempeture during a 2 hour high cruise. Vladimir indicated he has seen oil temps in the 230-240F range towing something relatively small. I expect to see oil temps in this range on long drives with vehicle little weight in the vehicle as well.

So this leads to the assumption between where the oil temps the 6.2l is operating at at highway speeds and the engine load percentages the 6.2l sees on the highway regularly with minimum weight in the vehicle or not towing a trailer, using 0W20 oil leave ZERO safety margin.

Add to this operating on less than 4 cylinders during DFM operation, Fuel diluted oil and Low Speed Pre Ignition, we wonder why 6.2l are having bearing failures.

What are the mechanics/physics behind warming the truck up for a considerable time and then driving for a short time that causes the oil to be thinned with gas? Why does this allegedly happen (or happen to a greater extent) under these circumstances? What's going on in the engine that's promoting the dilution?

 

[blanchard7684]

Thank you. So, what oil do you recommend running in the 6.2?

5w30 or 0w40. 0w40 if you are towing alot, or driving in high ambients frequently, or have to drive up steep grades often (and pass other vehicles).

I think you can get away with 0w20 in the 5.3 if you opt for a more frequent oil change interval. I've been running 0w20 in my 2024 5.3 Suburban because I bought a bunch of it. I have 8000 miles and three oil changes though...

 

[jfoj]

However, I drive 0-20 on oil without any problems, and I have 75 thousand miles, I drive fast. Fast means around 90-105 mph on the highway. or with a trailer at 80-90 mph. and I change the oil every 7500 miles. And this is the worst mode for 0-20 in your hypothesis. And I have no problems, neither with the oil, nor with the 6.2 engine.

@Vladimir2306

It seems you drive you vehicle very differently than many of us here in the USA. There are few places people can drive constantly at 90-105 MPH on the highway without being quickly followed up by traffic enforcement and at these speeds you can and will lose your drivers license and the insurance prices may increase and/or you may be canceled. I woudl say most drivers in the US depending on the local posted speed limit may only travel 5-10 MPH higer than than the posted speed. So this typically at most wil be maybe 80 MPH, more often I would expect the "Average" speed most are traveling on the US roads is between 65-75 MPH because many Interstate posted speed limits are 55-65 MPH, some are higher but it is more "State" dependant as there is really only a "National" 55 MPH mininum speed limit these days. Many years ago, the US had a "National" 55 MPH speed limit maximum.

So this being said, a the engine RPM you are operating at is in a better range with less low RPM "lugging". Additionally with the higher RPM and oil temperatures you are likely burning off any fuel contamination in the oil.

I also assume at these speeds and higher RPM that the DFM may be less likely to function unless you have it bypassed. Would also be interesting to see if you are triggering the 2nd stage in the oil pump on a regular basis at these speeds.

Do you typicaly use Trailer Towing mode when you drive at these speeds or when you are towing your trailer?

I also recall you mentioned that you had no problem getting Premium fuel in Russia, is this correct and what Octane rating is typically available?

Do you have any data for these 90-105 MPH drives that you can share?

 

[viven44]

However, I drive 0-20 on oil without any problems, and I have 75 thousand miles, I drive fast. Fast means around 90-105 mph on the highway. or with a trailer at 80-90 mph. and I change the oil every 7500 miles. And this is the worst mode for 0-20 in your hypothesis. And I have no problems, neither with the oil, nor with the 6.2 engine.

Just curious. What are the average high temps where you live ?

Just like any thermodynamic system, total temp = ambient temp + temp rise from power dissipation. Down here in TX where summer days are 100F and warmer a couple of months, on my old trucks I definitely use the higher viscosity option.

 

[blanchard7684]

What are the mechanics/physics behind warming the truck up for a considerable time and then driving for a short time that causes the oil to be thinned with gas? Why does this allegedly happen (or happen to a greater extent) under these circumstances? What's going on in the engine that's promoting the dilution?

DI engines spray fuel directly into the combustion chamber. When engine is cold, the "atomization" or mixing with air is or can be very poor. This leads to fuel droplets agglomerating especially on cold surfaces like cylinder walls. This will mix with lube oil and overtime create a fuel dilution in lube oil. It is a slow process but one that can take shape over an oil change interval of 7000 or more miles.

Combustion chamber design is set to cause swirl, squish, and quench. This is to promote mixing of fuel and air to be as uniform of a mix as possible. Swirl is circumferential motion, squish is radial motion, and quench is degree of uniformity vertically.(It also refers to clearance between head and piston at TDC.)

My opinion only--I think high swirl designs promote the fuel agglomeration on cylinder walls...

The contrast is with older port fuel injection (or carburetors) that mix fuel and air upstream of combustion chamber. The mixing is almost perfect.

Then of course fuel is a solvent for lube oils just based on the chemistry. So it will disrupt the "film" properties and essentially reduce the reaction force capabilities of the oil wedge.

So the more viscosity you start with, the more you can tolerate reductions before your eccentricity hits 1.0 which is technical metal to metal contact every revolution.

 

[Vladimir2306]

@Vladimir2306

It seems you drive you vehicle very differently than many of us here in the USA. There are few places people can drive constantly at 90-105 MPH on the highway without being quickly followed up by traffic enforcement and at these speeds you can and will lose your drivers license and the insurance prices may increase and/or you may be canceled. I woudl say most drivers in the US depending on the local posted speed limit may only travel 5-10 MPH higer than than the posted speed. So this typically at most wil be maybe 80 MPH, more often I would expect the "Average" speed most are traveling on the US roads is between 65-75 MPH because many Interstate posted speed limits are 55-65 MPH, some are higher but it is more "State" dependant as there is really only a "National" 55 MPH mininum speed limit these days. Many years ago, the US had a "National" 55 MPH speed limit maximum.

So this being said, a the engine RPM you are operating at is in a better range with less low RPM "lugging". Additionally with the higher RPM and oil temperatures you are likely burning off any fuel contamination in the oil.

I also assume at these speeds and higher RPM that the DFM may be less likely to function unless you have it bypassed. Would also be interesting to see if you are triggering the 2nd stage in the oil pump on a regular basis at these speeds.

Do you typicaly use Trailer Towing mode when you drive at these speeds or when you are towing your trailer?

I also recall you mentioned that you had no problem getting Premium fuel in Russia, is this correct and what Octane rating is typically available?

Do you have any data for these 90-105 MPH drives that you can share?

It is clear that I drive completely differently than the average American)) Fortunately, our toll roads in Russia allow us to move between cities quickly and comfortably.
The photo shows the revs at a speed of 170 km/h, which is about 105 miles per hour
But you just said above that it is fast driving under load and in the heat that kills the 0-20 oil. Well, it doesn't kill anything. The oil works fine. I repeat, I have 75k miles, and I change the oil every 7500 miles, without resorting to early oil changes. The only thing is that I change the fluid in the automatic transmission and transfer case and axles every 30K miles.
Yes, and I fill up with petrol grade 95 in Russia, which is about 91 according to the American standard. So there is nothing unusual, I just follow the regulations prescribed by the manufacturer.

 

[Vladimir2306]

Just curious. What are the average high temps where you live ?

Just like any thermodynamic system, total temp = ambient temp + temp rise from power dissipation. Down here in TX where summer days are 100F and warmer a couple of months, on my old trucks I definitely use the higher viscosity option.

I live in Moscow, Russia, it is a city with a moderate climate, in the summer we have up to 80+95F, in the winter it can be up to -22F. At the same time, I travel a lot around our country, visiting regions in the winter where it can be -50F, and in the summer I go to the Southern regions where 100-115F is not uncommon))) but my main place of residence is, as I said above, a region with a moderate climate.

 

[KMeloney]

DI engines spray fuel directly into the combustion chamber. When engine is cold, the "atomization" or mixing with air is or can be very poor. This leads to fuel droplets agglomerating especially on cold surfaces like cylinder walls. This will mix with lube oil and overtime create a fuel dilution in lube oil. It is a slow process but one that can take shape over an oil change interval of 7000 or more miles.

Combustion chamber design is set to cause swirl, squish, and quench. This is to promote mixing of fuel and air to be as uniform of a mix as possible. Swirl is circumferential motion, squish is radial motion, and quench is degree of uniformity vertically.(It also refers to clearance between head and piston at TDC.)

My opinion only--I think high swirl designs promote the fuel agglomeration on cylinder walls...

The contrast is with older port fuel injection (or carburetors) that mix fuel and air upstream of combustion chamber. The mixing is almost perfect.

Then of course fuel is a solvent for lube oils just based on the chemistry. So it will disrupt the "film" properties and essentially reduce the reaction force capabilities of the oil wedge.

So the more viscosity you start with, the more you can tolerate reductions before your eccentricity hits 1.0 which is technical metal to metal contact every revolution.

Fantastic explanation. Thank you!

Now, I was always told to "warm up the engine" prior to driving so that the oil had a chance to lube everything prior to high-RPM operation -- at that THIS is how you prolong the life of an engine. Is the reasoning behind NOT doing this that the engine doesn't actually get warmed up this way, or this provides a good amount of time for fuel agglomeration, or only actually driving the truck/getting into higher RPMs is what warms the engine sufficiently, or...?

Do YOU have any ideas as to why GM wouldn't at least recommend higher-viscosity oil (via a bulletin or something) at this point as a measure toward preventing engine failure?

 

[Vladimir2306]

Fantastic explanation. Thank you!

Now, I was always told to "warm up the engine" prior to driving so that the oil had a chance to lube everything prior to high-RPM operation -- at that THIS is how you prolong the life of an engine. Is the reasoning behind NOT doing this that the engine doesn't actually get warmed up this way, or this provides a good amount of time for fuel agglomeration, or only actually driving the truck/getting into higher RPMs is what warms the engine sufficiently, or...?

Do YOU have any ideas as to why GM wouldn't at least recommend higher-viscosity oil (via a bulletin or something) at this point as a measure toward preventing engine failure?

Great question, maybe because GM knows that the cause of engine failure is not oil?))