Oil Consumption

asilverblazer · June 16

21 hours ago, PunchT37 said:

1/2 qt over full ain`t gonna hurt $h!t. Most times, a whole qt won`t either. Most have windage trays now. As long as the crank isn`t slapping itself in the oil, it`s not the end of the world.

I agree.

However, the owner's manual, suggests that a drop over full is just as bad as a drop under. (Read black and white letters only, insert no common sense.)

PunchT37 · June 16

10 minutes ago, asilverblazer said:

I agree.

However, the owner's manual, suggests that a drop over full is just as bad as a drop under. (Read black and white letters only, insert no common sense.)

Oh please. Wonder what temp they measured the drop over?

Not bustin your ball$.

riddler · June 20

Thanks everyone for your input on this subject. It was very entertaining but not educational. Bottom line. The GM 6.6L should not consume oil, which it does, no matter the driving style. Only time will tell if it lasts past 100k. I am hoping 200k+.

GM needs to get back to the piston rings and top fuel injection which works and has been proven.

You may now move about the cabin.

c4racer2 · June 23

On 6/19/2026 at 10:01 PM, riddler said:

Thanks everyone for your input on this subject. It was very entertaining but not educational. Bottom line. The GM 6.6L should not consume oil, which it does, no matter the driving style. Only time will tell if it lasts past 100k. I am hoping 200k+.

GM needs to get back to the piston rings and top fuel injection which works and has been proven.

You may now move about the cabin.

I think the ship has sailed on the fuel injection type - everything is getting direct now. Does it help with mpg? Not really and nobody buying a HD truck really cares anyway. But that is what it is at this point. Piston rings is something they may well adjust over time to get them right.

riddler · June 23

Your right on.

asilverblazer · 2026-07-01T21:50:24Z

Update to my experience, my truck was due an oil change per the GM OLM, right at max mileage around 7500 miles.

As I've stated, the dipstick doesn't appear show a tremendous drop in oil volume over the course of a change, that needs some correction.

Just prior to pulling the drain plug I noted the level on the dipstick. It was about 2/3-5/8 down on the acceptable range, not 3/4 but more than 1/2 way down.

After refilling with the full 10 quarts, the dipstick measured at the top of the acceptable range - full. After noting these two dipstick readings at each end of the oil change interval spectrum, I might notice the gradual drop on the dipstick more easily during regular checks.

I measured the drained volume of oil and what came out of the drain pan was about 8 1/2 quarts.

To be below the add mark on the dipstick it would have to be about 2 quarts below the full 10 quarts.

BuckWallace · 2026-07-01T22:02:14Z

11 minutes ago, asilverblazer said:

Update to my experience, my truck was due an oil change per the GM OLM, right at max mileage around 7500 miles.

As I've stated, the dipstick doesn't appear show a tremendous drop in oil volume over the course of a change, that needs some correction.

Just prior to pulling the drain plug I noted the level on the dipstick. It was about 2/3-5/8 down on the acceptable range, not 3/4 but more than 1/2 way down.

After refilling with the full 10 quarts, the dipstick measured at the top of the acceptable range - full. After noting these two dipstick readings at each end of the oil change interval spectrum, I might notice the gradual drop on the dipstick more easily during regular checks.

I measured the drained volume of oil and what came out of the drain pan was about 8 1/2 quarts.

To be below the add mark on the dipstick it would have to be about 2 quarts below the full 10 quarts.

I'm confused on the 10 qts—the L8T takes 8 (7.9, actually) quarts with an oil/filter change.

asilverblazer · 2026-07-02T17:33:43Z

19 hours ago, BuckWallace said:

I'm confused on the 10 qts—the L8T takes 8 (7.9, actually) quarts with an oil/filter change.

My truck is diesel, L5P.

Chuck FB · 2026-07-02T18:14:42Z

26 minutes ago, asilverblazer said:

My truck is diesel, L5P.

LOL, its thrown a few people because this item is being talked about in the gas part of the HD forum. Probably wouldn't be a bad idea to put a very brief wording in your profile with the year/GM or Chev/2500 or 3500/ and yes the 6.6 Duramax. When I joined this forum I could see the confusion ensuing for my own truck unless I had it listed with my chosen name handle unless one has a few vehicles that apply to a GM forum as that becomes confusing as well. Anyway its all good, makes for a little forum excitement

Chuck FB · 2026-07-02T18:57:10Z

So speaking of oil consumption with my L8T as I just changed the oil yesterday and made the switch over to Amsoil SS 0W-40 from the Mobil 1 5W-30 Truck and SUV I just dropped out. 2900 miles on that oil as well as 68 hours on that oil ( so used to equipment with an hour meter and that becomes valuable information to compare with others as well ). Once again the oil use was so very little, I am going to say it dropped under 1/16 of an inch on the dipstick. No towing was done and this interval was from early spring until now.

One interesting item to note is that going by the 5 quart jugs I was using before from Mobil, it was showing that I was putting in 8 US quarts to bring it to full if not slightly over the full mark according to their jug markings. Granted I did allow more drain time this time and in part because the engine oil was only lukewarm as I started it and let it idle and not for long enough to get the oil itself hot ( the engine was up to operating temp ). The oil in that state just seemed to take forever for it to drip out but not only at the drain plug but at the oil filter housing as well, perhaps I had never quite gotten all the oil out before and I could have still waited longer but as it was I waited well over 3 hours. I think next time if I have the time I will do an experiment by dropping the oil and lets say leave the pan under it for 15 minutes, then switch to another pail and let it drip out overnight and measure how much more oil comes out. So this time and yes I ended up getting it just over the full mark as I was experimenting with trying to get the level to the add mark after I had run it and then waited some and then added a bit and waited for a certain amount of time for it to settle to the add mark. I very well may not have waited long enough for that experiment but I got to the add mark, then dumped in a full quart and waited some and checked and then waited some more and it crept up more ... and then finally oops, it was slightly over full some hours later when it really had settled all it would. I find this engine sure takes time for the last bit of oil that gets poured in to finally make its way into the crank case. I can only guess at how much too much I added as per maybe a 1/10th of a quart. I had poured in 8.5 quarts going by the quart containers as per 8 quarts and 16 us ounces. I was shocked at how much this was off compared to the prior oil changes and if those larger jugs and they are not marked accurately enough or they contain slightly more than what they say, or the drain time factor made that much of a difference. But I know on this forum there have been others who have said they have put well over 8 quarts in their L8T and now I have also going by the Amsoil true quart containers. Its a confusing convoluted mess up here in Canada with some oil manufactures packaging is in true US quarts, some is also in true US quarts containers on an even number of quarts but also marked in liters which becomes the odd ball volume of a fractional amount of liters. Then there is the Liters only containers, no US markings as its a true metric container and only measured in Liters to an even number of Liters. But remember we used to have Imperial Gallons and Imperial quarts as well !.

diyer2 · 2026-07-02T19:40:17Z

I have changed oil and filter for years by starting a cold engine to warm oil up, let it run 5-10 minutes depending on temperature.

Drain until it starts dripping, refill with quantity from owners manual or get it close.

Chuck FB · 2026-07-02T20:27:26Z

29 minutes ago, diyer2 said:

I have changed oil and filter for years by starting a cold engine to warm oil up, let it run 5-10 minutes depending on temperature.

Drain until it starts dripping, refill with quantity from owners manual or get it close.

Through the years it hasn't been my typical method as I tried to drop oil on an engine that was hot from having been worked, however that was not always practical and had to fire up a unit and let it warm up reasonably well and drop the oil when I had the time to do it but am referring to not only vehicles but a variety of farm equipment and highway tractors etc. However on a vehicle where one is crawling under it and the exhaust is nearby to ones body and if wanting to pull the plug without danger of being hit with boiling hot oil or attempting to remove a HOT oil filter, its sure safer and easier to not have everything smoking hot and can remove the filter right away when under the vehicle and let it all drain. Of course its not the end of the world if a bit of oil stays in the engine that might have eventually found its way out, I like to get out as much as possible but any oil changes that take place in shops would rarely be sitting around for very long at all before the plug is thrown back in and filter slapped on and oil poured in and sent out the door quick like. There would be very little time spent ( assuming they even did it ) in starting the engine with oil to fill the filter, then waiting to verify the level on the stick. A good reason to check ones oil level shortly after a shop changed the oil on a vehicle just to make sure its correct and to look under for any oil around the drain plug or filter.