Off Topic Archive

Locked: Car burns oil -What does that mean

  • Last Updated:
  • Sep 3rd, 2005 11:28 pm
Deal Addict
User avatar
Oct 5, 2003
3744 posts

Car burns oil -What does that mean

I found a used car for a good price and the guy said it used a little bit of oil. Whenever he gets an oil change it is down a little.

It that something to worry about? what does that mean if it uses a little oil?
12 replies
Deal Addict
User avatar
Nov 5, 2003
1606 posts

Bad valve seals

Worn valve guides

Pressurized crankcase (oil pan) due to a clogged PCV valve or breather system

Blow-by from worn piston rings

Bad valve seals: The valves are located in thecylinder head above the combustion chamber. Oil is pumped at 50 to 80 psi of pressure into the top of the head, lubricating the valve-train; the valveshave seals on them to stop the flow of oil down into the engine when the valve is open. If the seals fail, oil is allowed to flow down into the combustion chamber and is burned.

Worn valve guides: The valves are guided by a small cylindrical chamber called a valve guide. These guides wear over time causing eccentricity (or slop); the excess gap allows the flow of oil down the valve stem into the combustion chamber to be burned. What about the valve seal you say? Well, the gap is too great for the seal to stop the oil flow, so down it goes to be burned.

Pressurized crankcase due to clogged PCV or breather system:The car's engine is a giant pump, consequently it must breathe. The PCV (Positive Crankcase Ventilation) system does just this, allows the engine to exhaust the excess pressure build-up (which is a natural phenomenon of the internal combustion engine). Carbon build-up is a by-product of an engine and can build up in the PCV system, clogging the breathing passages. This in turn pressurizes the oil pan and pushes oil up into the fuel delivery system, where it is fed into the engine and burned.

Blow-by from worn piston rings: The pistons in your car's engine have seals around them in the form of rings. These rings do two things:


Seal the combustion chamber so the precious power developed from the firing of the cylinder is not lost.

Provide vital lubrication to the cylinder walls.

When the rings wear out, the pressure from combustion reverses down into the oil pan, pressurizing it and forcing oil into the valve covers, through the breather system, back into the fuel delivery system, and into the engine to be burned.

You may ask yourself, "What can I do to stop this from happening?" Keep your oil and filter changed every 3,000 miles and keep the air filters changed every 12,000 miles!! This will keep sludge and carbon buildup down to a minimum. Understand that you can't stop mechanical wear, but you can slow it down!

Now a word about new cars. People notice the engine in their new vehicle seems to be burning oil. They contact the dealer and are advised that using oil is a "normal condition." I agree, however there is a difference between "burning oil" and "using oil." We just discussed how oil is burned. In contrast, today's engines operate at higher temperatures and compression ratios, causing oil to be used. Higher temperatures and compression ratios achieve two things:


Lower exhaust emissions

More power out of smaller engines

However, along with these benefits comes the side effect of using oil, due to the increased friction and heat. As a result, the oil is evaporating or being broken down while doing its job. In other words, the oil is being used. It is not going out the tail pipe as it does when it is burned.

The rate of oil use depends on how much the vehicle is used and, more importantly, under what load. For instance, a 3/4-ton pickup truck used for hauling will use more oil than a small passenger car. For those experiencing a higher rate of oil use, I suggest using synthetic oil. It has a higher resistance-to-viscosity breakdown and will do a better job than standard oil.
Great Gossip Site - The Superficial
Deal Addict
Mar 14, 2004
2761 posts
North Etobicoke
Engine has to be rebuilt.

Justin wrote:I found a used car for a good price and the guy said it used a little bit of oil. Whenever he gets an oil change it is down a little.

It that something to worry about? what does that mean if it uses a little oil?
Deal Addict
Nov 21, 2004
1609 posts
Depends on how much it really burns. If it burns 1/2 litre every 5000km, probably not a real big deal. If it burns 1/2 litre every 500km, you realy don't want to own it.
Deal Addict
Apr 21, 2003
4647 posts
It means blue smoke comes out of the muffler and people behind you get very angry.
Deal Expert
User avatar
Jan 27, 2004
38328 posts
when it starts burning oil, it basically means your engine is dying.
Not exactly a good thing... burning oil is the thing you want to avoid the MOST when buying a used car b/c u never know how worst it could get.
Deal Guru
User avatar
Mar 1, 2004
12862 posts
Justin wrote:I found a used car for a good price and the guy said it used a little bit of oil. Whenever he gets an oil change it is down a little.

It that something to worry about? what does that mean if it uses a little oil?
What car is it and how old is it? Does it visibly smoke when you drive it, or not at all? The reason I ask is because older cars consumed oil frequently and it is not unusual to have to top it up every once in a while. Also if the oil changes weren't done frequently enough, any car would be down a bit. Nobody that changes their oil frequently notices 1/2 litre missing.
Some older performance cars (such as 1985-1992 5.0 Mustangs) have a forged piston that expands a lot when hot, so they don't seal well until the engine gets hot. These cars when driven semi-aggressivley will consume roughly a litre per month.

If you see blue smoke or haze while you are driving or smell oil from the exhaust, then you have internal engine problems.
Deal Guru
User avatar
Apr 16, 2001
14697 posts
BobW wrote:If it burns 1/2 litre every 500km, you realy don't want to own it.
Hell, a 2.0L Jetta does that. :lol:
Whenever someone asks a question that starts with "Why do they..." or "Why don't they...", the answer is always a) money, b) stupidity, or c) both.
Deal Fanatic
Jul 30, 2003
5285 posts
simple test : To test if its really a problem. Let the car sit for at least an hour then tell someone to start it (when engine is cold) and if you see smoke coming out ... walk away

- Redline the car in any gear and see if there is smoke in the back (preferable someone behind / outside the car observing) ... also when the engine is hot (cuz u shouldn't do this on cold engine)
For Sale:
  • Canon C100 + Canon 70-200 f2.8 + ...
Looking for: Sony Camera for video (for a good price)
Deal Addict
User avatar
Feb 26, 2005
1944 posts
1 upvote
Might not pass a drive-clean if it burns oil.
Deal Addict
User avatar
Nov 8, 2004
1361 posts
for your sake, dont buy it. you me be in over your head in this.
Deal Addict
User avatar
Apr 19, 2002
2116 posts
Remanufacturing an engine costs $3000-4000 to bring it back up to spec. It might be half that cost if it's just the valve seals. An engine replacement from a wreck can run in the $2000-3000 range. Be very careful if a car is burning oil.

Watch out for sellers who will drain all the oil from a car to make it stop smoking out the tailpipe. The car might run for a short test drive and not appear to be smoking, but it's because there's no oil in it! Check the dipstick (take out, wipe, replace, and remove to examine) to make sure there's clean oil in the engine. Make sure to have the owner start the car with a cold engine while you are behind it to check the emissions. Have them rev it a bit too.
User avatar
Nov 28, 2002
408 posts
That you posted in the wrong forum.