I just don't get it……..

Status
Not open for further replies.
Joined
Jan 13, 2016
Messages
3,488
Location
Northeast Nebraska
I'm reading a thread and the gist is how much better engines are today because of the tighter tolerances engines are built to. Then I go to a thread where some of you say it's nothing to worry about when an new engine uses a couple quarts of oil between changes. This makes no sense to me.

I've only owned two vehicles that used oil but they were farm trucks that had the life beaten out of them by the time I got them. A 67 chevy and a 69 GMC both 1/2 tons one with a 283 and one with a 250 six. All the other vehicles I've owned have not used oil to where I had to add between changes. I've also never owned anything newer than my 99 Buick.

What am I missing here guys?
 
Not sure, but my friend's 2005 F150 4.6 goes 8K between oil changes (always Super Tech synthetic) ... has 171,000 miles and never uses a drop.
 
I don't know why but all the engines I've ever had used some oil. My current car, an 06 Malibu, just keeps consuming more and more oil as it ages. Up to 1qt/4000 miles now. UOA show very little wear metals. Low friction rings?
 
When I rebuilt my 84 Civic the machine shop that did all the need machine work used some kind of special machine to hone and match the cylinders to the pistons.

I now have something over 20K on the rebuild and I can't see any movement on the dipstick between 10K oil changes. This is with 0w-30 synthetic oil.

Then a neighbor buys a new Mercedes and at 50K miles it's burning a quart between 500 and 1K miles using dealer supplied oil and service. The dealer tells him this is normal. Do you think I should call up Mercedes in Germany and give them the phone number of the machine shop that did my engine? lol
 
If engines were built to higher & higher tolerances over the decades, the internal engine parts wouldn't be able to move in the engine.

I think/believe that when people say "tighter tolerates" that the really mean that engine spec's have been tightened closer to the center of that specification. In other words, what is acceptable to the engineers as compared to yesteryear.

What was allowed to pass inspection years ago wouldn't even hold a candle to todays production. What was allowed to leave the factory years ago would be considered a FAIL today by Quality/QC or line inspectors.

So, are the internals of an engine that much tighter than lets say, 40 years ago? A little!
I mean, everything today in the automotive world is designed differently as well for fuel economy, emissions, longevity etc.
 
Originally Posted By: Olas
Tolerances are not the same as clearances.


Correct - and a lot of engineering has been done to reduce the amount of clearances (rather, tighter clearances) because parts don't expand/contract as much has before.

High-silicon content Hypereutectic pistons are a perfect example.
 
I've been led to believe they reduced tension in piston rings to reduce friction losses. This allows more oil to bypass the rings.
 
Originally Posted By: Char Baby
If engines were built to higher & higher tolerances over the decades, the internal engine parts wouldn't be able to move in the engine.

I think/believe that when people say "tighter tolerates" that the really mean that engine spec's have been tightened closer to the center of that specification. In other words, what is acceptable to the engineers as compared to yesteryear.

What was allowed to pass inspection years ago wouldn't even hold a candle to todays production. What was allowed to leave the factory years ago would be considered a FAIL today by Quality/QC or line inspectors.

So, are the internals of an engine that much tighter than lets say, 40 years ago? A little!
I mean, everything today in the automotive world is designed differently as well for fuel economy, emissions, longevity etc.


I think part of it is also there is less variance between engines. You could have 2 Chevy 350's with identical parts that were totally different in performance due to all the small differences in parts adding up. Today, the 2 identical engines built would be very similar in power.

Originally Posted By: Olas
Tolerances are not the same as clearances.

Totally.
 
One thing to consider: Oil change intervals have gone way up. If your car consumes a quart every 4k, it'd never need top-off with 3k OCIs -- but with 10k OCIs, it'd need two quarts.
 
Originally Posted By: d00df00d
... If your car consumes a quart every 4k, it'd never need top-off with 3k OCIs -- but with 10k OCIs, it'd need two quarts.
That's a good point too often ignored. Change intervals and consumption rates are separate issues. I wish people would shut up with muddling them together by talking about consumption per change interval. If (hypothetically) advances in oil composition allow doubling the change interval, that's no reason to assume consumption per unit distance will automatically drop by half.
 
Last edited:
Better engineering, better metals, better CAD repeatable parts, better ignition systems that are ECU driven, VVT, better cooling, really just better everything.
 
Originally Posted By: WobblyElvis
I don't know why but all the engines I've ever had used some oil. My current car, an 06 Malibu, just keeps consuming more and more oil as it ages. Up to 1qt/4000 miles now. UOA show very little wear metals. Low friction rings?
Originally Posted By: Olas
Rings or stem seals or PCV.

They all use oil but if it's a measurable amount within an OCI you need a mechanical repair.


I'd say PCV. My Malibus throttle body was covered in oil. I tracked it to the "PCV valve" built in to the valve cover. Mine uses significantly lessthough , 1/2 qt per 5k miles. The car only has 51k miles on it though.
 
There are tolerances, and there is tolerance matching. OEMs use tighter tolerances in design with CAD and manufacture with tighter tolerances with CNC machining. Back in the day, mass manufacturing of an engine involved tolerances in the thousandths of an inch; today it's in ten-thousandths of an inch.

What that cannot do is match tolerances on an individual engine basis (or more accurately, they do so on a limited basis defined by their mass manufacturing limitations). For that you may need someone who can run user-operated machining. The old machinists who are skilled at that are dying out, so it's more difficult to find today than in the past, but there are some who embrace it and those are the guys you want to build your engine.

Building part A to a tight tolerance and part B to a tight tolerance does not mean the two will mate within a tight tolerance; they could add up to the widest possible variation. A skilled machinist will measure and machine so those two parts mate ideally. There will be differences in the outcome.
 
Originally Posted By: blupupher
Originally Posted By: Char Baby
If engines were built to higher & higher tolerances over the decades, the internal engine parts wouldn't be able to move in the engine.

I think/believe that when people say "tighter tolerates" that the really mean that engine spec's have been tightened closer to the center of that specification. In other words, what is acceptable to the engineers as compared to yesteryear.

What was allowed to pass inspection years ago wouldn't even hold a candle to todays production. What was allowed to leave the factory years ago would be considered a FAIL today by Quality/QC or line inspectors.

So, are the internals of an engine that much tighter than lets say, 40 years ago? A little!
I mean, everything today in the automotive world is designed differently as well for fuel economy, emissions, longevity etc.


I think part of it is also there is less variance between engines. You could have 2 Chevy 350's with identical parts that were totally different in performance due to all the small differences in parts adding up. Today, the 2 identical engines built would be very similar in power.

Originally Posted By: Olas
Tolerances are not the same as clearances.

Totally.


Well said!
smile.gif
 
Originally Posted By: Olas
Rings or stem seals or PCV.

They all use oil but if it's a measurable amount within an OCI you need a mechanical repair.


What do you mean by "need"?
 
Originally Posted By: oldhp
Better engineering, better metals, better CAD repeatable parts, better ignition systems that are ECU driven, VVT, better cooling, really just better everything.


Which, if its true, doesn't answer the OP's question, which was, essentially, why do some new cars (anecdotally, they often seem to be German) have relatively high oil consumption?

We've had longer change intervals (so the consumption per mile may actually not be much higher) and less ring outward pressure as suggestions.

Maybe skinnier oils, which may shear still skinnier during that longer change interval, might be relevant too?
 
Status
Not open for further replies.
Back
Top