Why does an engine loose oil?

[rvitek]

It's no big deal and I know it's 'normal' for an engine to use oil during operation. But, why? My XLT uses one quart at 4500 miles (on a 9000 change interval) and my SLS uses one quart at 3K and 6K (during the same cycle). What causes this? And no, I don't have any leaks

Thanks!

Ry.

 

[Howard]

Oil gets into the combustion chamber via a number of roots. Passed the valve stems, piston rings and via the oil breather system. As an engine wears the gaps get more and more so the engine uses more oil. Hope this helps.

 

[Black Magic]

Are you tightening the drain plug? LOL J/K!

 

[Alec]

Ryan,
Just to let you know, my uncle's Northstar was losing about a qt every 1500 miles and eventually the motor crapped out and he got a new Caddy. Caddy said it's normal for those V8s to lose oil and a qt every 3000 is normal. If you ask me though, that's bullsh!t.

 

[rvitek]

Originally posted by Black Magic
Are you tightening the drain plug? LOL J/K!

YA!

Alec - yea, I discussed this with the dealer on Thursday and they said 1Q per 3K miles is within normal operating range, whatever that means. I will keep an eye on it and if it does get worse, I'll definately take it in - how many miles did he have on it when they replaced it?

And thanks Howard - I undersand now. Does the oil get vaporized and out it goes? I'm not familiar with the breather system, can you explain?

Thanks!

Ry.

 

[aldive]

Using oil is not normal. I have almost 75k miles and it has never used a drop.

 

[tbomb]

2 ways to lose oil...

1) like howard said, its could get burned, and spit out the exhaust.

2) its leaking.

and aldives right. its not normal to lose oil.

 

[andypinto]

I agree. loosing oil is not normal.
If rvitek has no leakings in the engine, so the oil is been burned (at slow rate, 1 qt each 3000m). As long I know, (and please correct me if I'm wrong) the oil is burned when it pass to the combustion chamber, and this happens in two ways: through the valves or through the piston rings.
In both situations I believe that an reduction of the compression rate will be noted in the engine.
Maybe a compression check will be a good idea to isolate the problem.

Good luck!

 

[Alec]

Ryan, I think the car was about 4 years old.

With any other motor, a qt every 3000 miles would send it to the rebuild shop. I don't understand how Caddy can have motors that do this routinely.

 

[Howard]

An explaination of the oil breather system. The cylinder block is not an air tight box (otherwise it would explode). So a vent is fitted. Now if this vent were to let the fumes go into the atmosphere it would cause polution so the vent ,via a flame trap, is connected to the intake manifold so that the fumes are burnt during combustion, hence the erg valve. These days with the modern emmision control system it is much more complex but the principal remains.

By the way all engines burn some oil even if in very small amounts but increased oil comsumption is a sure sign of exsesive wear in the moving parts and should be looked at. There are design issues and some engines are designed to use more than others.
Hope this helps.

 

[jazz_master221]

my 1997 ford f350 diesil company truck use about 1 quart every 3500 miles there's no leaks so it must be going into the cumbustion chamber....i've got 96000 miles on it and the only major problem has been the tranny ...rebult several times..but the truck ways in about 12,ooo# so it's way over loaded.........i work for US FILTER and we have a fleet of ford trucks....they hold up very well considering the abuse ....

 

[Texan01]

Oil consumption is based on a number of factors: (as quoted from memory from my 1974 Chevrolet service manual, Very good book for theory of operation on many aspects of autmotive design)
1. high engine speed will cause increase consumption due to higher manifold vacuum.

2. wear in the piston rings, valve stem seals, intake gaskets.

3. PCV system could be plugged.

4. Improper oil viscosity, too thin of an oil will burn at a more rapid rate than a thicker oil.

Some engines are more prone to oil usage than others. Lawnmower engines are almost always ran at WOT at maximum RPM so they will use oil at a greater rate than say a car engine which is why you would use 30 or 40 weight oil in them rather than a multi-viscosity.

That said, my Chevelle used to get about 400 miles per quart, till I rebuilt it, the engine still burns it at about a quart per 2000 miles due to excessive bore clearance (230,000 miles on the block, time for an overbore from standard). My Explorer gets 5000 miles out of a quart, and my old 6000 would go the whole 4000 mile interval without using a measuarable amout.


Dang that was long. sorry for the length

 

[dogfriend]

I have had engines that burned one or two quarts between changes and other engines which did not burn any between changes.

The reasons that an engine burns oil have already been stated by others, but I wanted to point out that it isn't unusual to burn some oil.

If you abuse your engine, particularly when first breaking it in, it is possible for it to burn more oil that it otherwise would have (i.e. don't drive a brand new engine at sustained high speed like a female former co-worker of mine did. She drove at 70mph for 2 days straight and her engine always burned oil after that)

Also, the type of oil you use can have some effect. If you have a relatively tight engine, synthetic oil may cut oil use, but if the engine burns lots of oil anyway, syn oil may increase oil use.

The part of the oil that "burns" are the shorter molecules that are part of the collection of various length molecules that make up the oil. They are able to squeeze past the rings, valve stems, etc. into the combustion chamber.

 

[Stephen]

My Cadillac STS Northstar also burned about a quart every 3000 miles, and my Caddy dealer also said it was normal for the engine.

The engines also have some bad sludging issues...

 

[Majisto]

Originally posted by Stephen
My Cadillac STS Northstar also burned about a quart every 3000 miles, and my Caddy dealer also said it was normal for the engine.

The engines also have some bad sludging issues...

Is the Northstar V-8 related at all to the LS1 V-8 in the F-bodies? I know those engines also have an oil consumption problem...

 

[JDraper]

Ryan, nobody has asked these questions yet, but what weight oil are you running in the motors and what mileage is on them??

My wife's Firebird 2.8L V-6 is supposed to run on 5W30, but if we do that, it eats a quart every 300 miles or so, but by using 10w30 we go about 1k before it uses a quart. We know the valve seals are worn, but it just hasn't been worth ripping the motor apart to fix it. It's been running like this since we bought the car with 48k on the motor and it has over 100k now.

 

[rvitek]

Thanks guys for all your posts and now, I have a very good understanding of why an engine may loose oil.

I've since polled the owners over at the Cadillac forums to find out what their dip-stick looks like at a full 7.5 quarts of oil, so that I can do a comparison of where I'm at right now with 2K miles on this oil change. I'll then bring this up with my dealer to see what they have to say about it.

Nothing I can really do on my XLT, as it's out of base warranty - but I'll ask the dealer the next time I'm in there.

Thanks again guys!

Ry.

 

[rvitek]

Originally posted by JDraper
Ryan, nobody has asked these questions yet, but what weight oil are you running in the motors and what mileage is on them??

The 4.6L Northstar has 27K miles on it running 0W30 oil.
The 5.0L XLT has 47K miles on it running the same, 0W30 oil.

As a test, I'm going to switch back to GM/Ford-recomended oil-weights and dino oil on the next change to see what kind of consumption I get.

I have the extended warranties on both of these vehicles and I want to keep them a long time - so I'll keep up on this to find out what the problem is.

Ry.

 

[Ross-N-Chicago]

Ryan,

My X needs vlave stem seals so I am using a lot more oil than I would like but she's going into the shop next week to fix it. One way to find out if your rings are worn is to pull the PCV valve out while running--if it is smoking than you have excessive crank pressure from worn rings. Mine doesn't do that so I can only trace it to valve stems. No oil leaking either.

 

[Stephen]

Originally posted by Majisto
Is the Northstar V-8 related at all to the LS1 V-8 in the F-bodies? I know those engines also have an oil consumption problem...

I dont think they are, but I could be wrong.