Jetta: Too Much Oil

I own a 2001 VW Jetta. Yesterday, the oil light came flashed. I checked the dipstick and it was completely dry (I had driven 2,000 miles since my last oil change). Stupidly, I was thinking that oil tank was was completely empty (of course, just because the oil level doesn’t reach the dipstick, it doesn’t mean that the oil tank is empty). I placed 4 quarts of oil into the oil tank (the tank holds 4.7 quarts). I quickly realized my mistake after seeing how high the oil level was on the dipstick. I had to get to a work meeting, so I drove about 6 miles. After the work meeting, I did not drive any more, and I was able to obtain an oil pan and empty enough oil out so that it showed the correct amount on the dipstick.

Question: Should I be worrying about driving 6 miles with too much oil?

Well, driving 6 miles with a grossly-overfilled crankcase is not good, but it was probably less injurious than having driven for…probably…well over 1,000 miles with insufficient oil in the crankcase.

Lesson #1: The “oil light” is most likely an oil pressure light, not an oil level light. When there is insufficient oil pressure, damage to engine bearings, cylinder walls, etc is the result. Unfortunately, you cannot turn the clock back to undo the damage that resulted from driving with a low oil level, but you can learn from this experience, hence…

Lesson #2: The dipstick should be checked fairly frequently on any car, and as a car ages it should be checked more frequently. Apparently, you are not in the habit of checking the oil level between oil changes, and you have to correct this type of negligence. Now that your car is clearly consuming oil, you need to check that dipstick at least once a week. If you continue to rely on a warning light, you will probably wind up destroying an engine that has already sustained damage.

Lesson #3: The part of the engine that holds the oil supply is the crankcase. It is not “a tank” in the same sense that your gas tank is a tank. You can run your gas tank fairly low without problem, but an engine needs to have its oil supply as close to the full level as possible at all times, and with a crankcase that holds as little oil as yours does, you can really do a lot of damage by running the engine with only about half of its normal oil supply. The object of checking the dipstick frequently is to never let the oil level fall more than 1 qt below the full mark. Personally, I replenish the crankcase as soon as the oil level has dropped by 1/2 qt, and my crankcase holds 7 qts!

Lesson #4: When adding oil, add it a little bit at a time, wait for a minute or so for the oil to drip down to the crankcase, and check the level. Do this several times, adding no more than 1/3 of a qt each time so that you don’t overfill the crankcase. Overfilling is bad because it causes the liquid oil to be churned into a foamy mass, and that foamy mass doesn’t lubricate properly.

Thank you, VDCdriver, for such detailed lessons. Do you think I should pay to have the car checked out to fix the possibly low oil pressure problem? And/or to find out if any damage was done during the 6 miles of driving with the oil level too high? Thanks.

What you should do at this point depends to a very great extent on how long you are planning on keeping this car.

If you plan on keeping it for more than a few months, then you might want to have your mechanic do a compression test on the engine, and I would suggest both a “wet” test and a “dry” one. This will tell how much excess wear has taken place on the cylinder walls and piston rings.

Other than a compression test, the only other thing that would show how much damage might have been done would be to…literally…tear down the engine for examination. I don’t think that anyone would suggest going to that expense on an 11 year old car with…God only knows…how many miles on the odometer.

On a practical level, I would suggest those compression tests AND taking a much more proactive approach to maintainance. In addition to checking that dipstick weekly and doing oil changes on schedule…When was the last time that you changed the transmission fluid? If the answer is “never” or “I don’t know”, the car may be reaching the end of its useful life anyway.

Thanks again, VDCdriver. The mileage on the Odometer is 88,000. I don’t know when the transmission fluid was last changed… I just bought the car used 4 months ago.
I’ll look into having the work done on the car.
Thanks for all of you help.

I would hold off on VDC’s suggestions for a little bit. The first thing I think you should do is monitor your oil consumption. Check your oil level every time you fill your gas tank to determine how bad the problem. If it turns out that your rate of consumption is about a quart per 1000 miles or less, then you may not need to do all the diagnostics, just keep up with the oil.

If the engine is consuming more oil than that, then proceed with VDC’s recommendations. But do check that transmission fluid. At 88k miles, it would be very close to the 90k drain and refill mark so your about due regardless.