Oil consumption & blowby problems.
Whenever you are looking for an oil consumption problem, you start by changing the oil, logging the miles and checking the dipstick weekly. DO NOT add oil unless the level is AT OR BELOW the add mark. All engines use oil, some more than others and 90% of all engines are MORE than a quart low at 3k miles. That would mean that at around 2000-2500 miles, they were a quart low.
The MINIMUM level of usage is a quart every 750 miles, according to all the car makers. While that would be totally unacceptable for a new car, that is where we start planning the overhaul of an older engine.
Once you verify that you are using more than a quart every 1500 miles or less and you know you don't have an external oil leak, you would begin by pulling the spark plugs which will tell you which cylinder(s) is burning the oil. By performing a leak down test and a wet / dry test will then tell you if it is a piston ring or valve guide or seal problem. If your oil level is still above the add mark at 1500-2000 miles, everything is fine.
Piston ring problem --- No choice but to either wait it out or fix it by overhauling or replacing the engine. Cost will vary between $1500-4000 depending on the engine size.
Valve guides or seals --- IF you have a puff of blue or grey smoke from the tailpipe in the morning, IF you don't have any other smoke throughout the day, IF you have a very minor oil usage problem, IF you have between 60k to 100k on the old clock (speedo), all of that points to bad valve guides or seals. My advice is never fix this very expensive repair UNTIL you begin to use a lot of oil AND oil foul your spark plugs. Often you will have this "puff of blue or grey smoke first thing in the morning and never again during the day" for years before you foul your first spark plug.
You see, no one can be sure if your oil consumption problems are because of bad valve guides or seals. The seals typically cost $300-800 depending on the engine but to pull the heads and rebuild them will cost $950-2200. So what happens if they think it's bad seals and do all the work to replace them, and that doesn't fix your oil consumption problem? All of that money was wasted and you still have the same problem.
Excessive blowby is often seen as oil in the air cleaner. The PCV or positive crankcase ventilation system's job is to vacuum the pressure out of the engine that is created by combustion leaking past the rings. When there is more pressure inside the engine than the PCV can handle, the excess pressure and oil mist is forced up the fresh air intake hose and into the air filter area or box.
Typically the car owners will first see their air filter soaked in oil and wonder how the oil got there. When this happens, the question is "Is there something wrong with the PCV system or is it being overcome by excessive internal pressure created by a bad piston or by bad rings?". Because anytime you have blowby problems, it's going to be related to one or the other.
On the PCV system, the vacuum port can get clogged with carbon, the rubber vacuum hose that goes to the PCV can collapse or the PCV valve can be bad. All of these will stop the vacuuming of the crankcase and allow excessive blowby. So always start at the vacuum port and work your way to the PCV valve.
If the PCV is fine, then your blowby problem will be because of a bad piston or bad piston rings. You can use a thicker oil like a straight 30 weight or 40 weight to slow down the oil usage and blowby but the best repair would always be to fix the combustion leak, which means overhauling or replacing the engine.
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