Oil Consumption by Design

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Some engines, such as volkswagen engines, are famous for consuming oil by design. As much as 1 liter per 1000 mile
smile.gif

My question is, does this theoretically mean less ring tension, thicker oil film at the cylinder wall, thus less wall and piston rings wear ?
 
Ive seen some high mileage engines with the original hone marks still in the cylinder walls. I dont piston wear is not a problem within warranty period. There must be another reason. The race community burns some oil to make more hp. I wonder if this is what they are doing.
 
My wife owns an Audi and I own a VW Golf GTI. I need to add 1/2 a quart at the 4K mile mark and I change the oil every 5K miles.
My wifes Audi doesn't consume enough oil to make it worth adding.
I have heard some engines consume oil by design. Sounds silly but who knows?
I'm a semi mechanic and another much older mechanic told me some engines have soft piston rings that seal great
but wear out faster and some engines have harder piston rings that last longer but don't seal as well.

Years ago when I was building a small block Chevy, he told me the cheap Hastings piston rings are great for 60K! thousand miles
and the engine will start burning oil.

Click on the piston rings and learn something:
https://www.hastingspistonrings.com/aftermarket
 
I think pretty much every modern (post emissions-era) engine burn oil "by design" because it's mandated that oil blow-by can't vent to the atmosphere. A typical emissions setup has the PCV valve connected by a hose to the intake, where blow-by gas (oil vapour from the bottom of the crankcase) burns with the intake charge.

As any internal combustion engine will have pressure and temperature variations that are going to create blow-by gases; something has to be there to take care of it. Pre-emissions engines just vented it to the atmosphere (oil "breathers" on the intake valve cover(s) ) or going back to the 50's and earlier just let it drip onto the ground.

You can alternately vent the blow-by gas to a catch can, racers do this, but that means emptying the catch can periodically. No OEM is going to make owners do that.
 
Originally Posted By: NICAT
Some engines, such as volkswagen engines, are famous for consuming oil by design. As much as 1 liter per 1000 mile
smile.gif

My question is, does this theoretically mean less ring tension, thicker oil film at the cylinder wall, thus less wall and piston rings wear ?


Cart horse inversion...

Low tension rings are to reduce drag, not wear, and oil consumption is (often) a result...which manufacturers then try to pass off 1qt/1,000 miles as "normal"...then when it's too bad, they add a dipstick with an altered "normal range" so it doesn't look so bad...then mandate lower P to protect emissions control devices on the ones that are bad, but now "normal".

No-one is purposely designing oil consumption IN to an engine (except for e.g. Mazda Rotaries). Their designs are causing increased oil consumption for other factors.
 
My last 6 engines which were sold at 100,000 + miles never used more than 4 oz of oil in a 6,000 mile OC. Saab 2.0/Jeep 4.0/Subaru 2.5L/ Mazda CX7 and now my Mazda 2.5 at 42,000 miles. I think those engines were better engineered. Ed
 
Better broken in I think.

Modern designs are all standard out of the box fit, not select fit like a '57 Chev was, or a 1970s Rolls Royce.

As a result, every engine is on average...well average in the fleet.

You can get an engine with tolerance stack up that makes it a burner, or marginally too tight (friction wise).

Only variable that you have in an "average" engine is to break it in properly.
 
I'm still wondering why the 8.1 in my 2001 3500HD has used 1qt every 750 mi since new no matter what oil I put in it.
 
Originally Posted By: skyactiv
My wife owns an Audi and I own a VW Golf GTI. I need to add 1/2 a quart at the 4K mile mark and I change the oil every 5K miles.


Why bother adding? Is it at the add level, or will be soon at the add level? not saying it's a waste of oil, just not sure it's worth the effort. [I used to have a Saturn, got to the point where I'd add a qt around 2k, then at 3k it was a qt low again--so I'd just have it changed. I tried to time it to save on oil. But perhaps not the best automotive example.]

Originally Posted By: ShieldArc
I'm still wondering why the 8.1 in my 2001 3500HD has used 1qt every 750 mi since new no matter what oil I put in it.


Seems high, but, those were big cylinders. Lots of surface area for those rings to scrape. Not sure it's linear, but at 8.1L it's four times the size of the "standard" 2L I4. So, waving my hands a bit, 4x the oil consumption seems plausible. If so, be glad that a qt every 400 miles wasn't deemed acceptable by the OEM!
 
IMO, the 'all engines consume oil' thing is a fraud practiced by certain OEMs. They figured out decades ago how to adequately seal the combustion chambers from the rest of the crankcase (and by 'adequately', I do not mean completely). The problem is that that level of sealing comes at the cost of fuel economy. As Shannow said above, one of the easiest & cheapest things an OEM can do to improve fuel economy is move to thinner, low tension rings. I don't know for sure but I suspect some have also been increasing the bore to piston side clearance. Of course all of this 'removal of resistance to flow' makes it easier for blow-by gas to get passed the pistons.

Now superimpose on this to a shift to higher compression ratios (for fuel economy or in the case of Turbochargers, performance), higher Noack oils (as a result to moving to thinner, fuel economy oils) and you get the potential for more engine oil to be routed around the PCV system and burnt. The effects of this progressively worsen as the engine ages. So it's a case of OEMs trading (on your behalf) short-term economy & performance credits with medium term engine problems (which might not surface until you're out of warranty). Unsurprisingly, they are somewhat coy about fessing up to this but it is definitely the game that's being played here.
 
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BMW went through this with the S62 and that was part of the reason for the spec for 10w-60, to help control consumption. The pre 03/00 engines could consume obscene amounts of oil and it was "par for the course" as per BMW. The post 03/00 engines had greatly reduced consumption due to updated rings, mine was reasonably good, only consuming ~1L/8000Km IIRC. One of the cars I looked at when I was shopping was a '99 that drank 1L/1000Km.
 
I guess I got lucky. Our 1996 Zetec 2L Contour even at 115,000 mi still doesn't use any really measurable amount of oil in even a 8,800 mi OCI. Our 195,000 mi 2005 4.6 V-8 Explorer again doesn't use any really measurable oil in a 9,000 mi OCI. Even our 2017 Explorer with the 2.3 EB doesn't use any really measurable amount of oil in even a 7,000 mi OCI. Low tension piston rings are suppose to help with gas mileage but increase oil usage I heard. And with our 2017 Explorer there doesn't appear to be enough measurable fuel diluting to the oil to keep the dip stick level up per my two UOA's.

Whimsey
 
Only engine I've heard of that was designed to burn oil were the Mazda Wankel. They have an oil injection pump that takes oil out of the sump and injects it into the rotor chamber for lubrication of all the side and rotor tip seals. I had two RX-7s and they used about a quart every 3000 miles, by design.
 
All engines have to consume oil, all of them, but the normal amount, on a healthy engine with properly broken in and not stuck piston rings, will not be noticeable on the dipstick or the change in the level should be minimal.

For engines over 100k miles, if the oil level stays between the min and max lines for the entire OCI, I would consider that normal as well.

And low tension piston rings are nothing new, it's just something people like to repeat to convince themselves and others that it is normal. You repeat it enough times and it becomes the truth.
 
No engine should consume oil "by design" unless it's a 2 stroke or a Rotary Wankel. Anything else is failure IMO, and sure there are plenty of engines out there without the adequate "piston ring seal by design". Very few engines, if any, out there have perfect finishes, but judging by passive oil consumption rates/problems, you can very easily tell which ones have the best finishes.
 
"Oil Consumption By Design" is what car dealerships tell you when you complain about excessive oil consumption.

This is their explanation to cover up bad design, bad engineering, bad manufacturing.

GM does this a lot.
 
The vehicle that used the least amount of oil is my 2005 Tacoma with the 4.0L V6. Based on careful oil level checks, it uses ~2 oz in 5,000 miles, which equates to 1qt/80,000 miles. Hard to believe, but that's what I see.

My C5 Z06 used about 1 qt/3500 miles until I put all new valve guide seals in it when I installed more robust valve springs and push rods. Some of the factory installed valve guide seals must not have been perfect, because the oil use rate went down to around 1qt/6,000 miles after new seals were installed.
 
Originally Posted By: KrisZ
Originally Posted By: PeterPolyol
No engine should consume oil "by design" unless it's a 2 stroke or a Rotary Wankel.


Can you explain then the purpose of the crosshatch finish on the cylinder walls instead of mirror like polish?


Among a few other reasons, what you're probably getting at is it's function to 'hold' lubricating oil for the sake of the rings The 'hatches' are designed to hide oil in them as the rings lap the bore. When the hatches are too deep, like in racing style hones seen in performance engines and the infamous Cadillac Northstar, or when the rings are not adequately shaped in situ by the break in asperities, then the resulting "finish" is faulty IMO (not so much in race engines but street engines, absolutely). Honing crosshatches are in no way ever intended by the engineer to specifically consume the oil; that's merely a consequence of wildly varying degrees- some engines consume no significant or perceptible amount of lube oil, even if they technically 'burn oil'. What I call oil burners are the ones who's consumption is not only noticeable, but problematic and inconvenient.

Secondary relation to oil consumption and the resulting finish of the bore hone, is the final shaping of the rings against the bore during break-in (the bore is never perfectly round all the time)
 
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