Oil in car

Is too much oil in my car bad for the engine? I think I put in a quart too much - should I have it drained or not worry about it?

(Car’s an Audi V-8 Quattro)


Yep, it can be bad. Too much oil can cause the oil pressure to be too high, which can blow the seals. Check the dipstick and drain it till it is at the right level.

Thanks much.

LOL, I work part time for a cab company. One day I’m preping my cab for a shift, which includes checking the oil level, and a new driver I hadn’t seen before asks me where the supply of motor oil was. I direct him the the 55 gallon drum of the stuff and he says thanks.

I go off to BS with my dispatcher for a few minutes before hitting the streets and when I get back this guy had filled the entire crank case of the cab he was to drive and says to me that the engine must have been bone dry because he couldn’t see any oil in there. I asked him if he meant the oil level on the dip stick and he asked “what’s a dipstick?” Well we had him park that cab till the excess could be drained by the mechanic.

Our company is big on nicknames and after three years that poor guy is still called “dipstick” to his face.

You might want to scour through cartalk.com for some information. I vaguely remember that according to Tom and Ray, up to one quart over full was probably not damaging. I quickly searched there just now but couldn’t find anything.

And always check your oil level when the engine is cold. [sub][sup](That statement oughta spark a debate!)[/sup][/sub]

I remember the Car Talk article that Kamandi’s referring to, as well - I believe this is it.

In addition to the possibility of having excessive oil pressure, if the oil is deep enough that it reaches the crankshaft, you can have problems. The crankshaft can (say Tom and Ray) work the oil into a nice froth, which tends to seriously impede its lubricating ability.

Good evening,

29 years ago, I came home from work. The pretty girl that had just moved in across the street was sitting in her car, crying. The car was billowing blue smoke, and running terribly. It seems she was trying to be self reliant and change her oil. She called her father and asked how much oil to use in an oil change. He told her 4 quarts, 5 if she changed the filter. She didn’t know where the filter was, but put 5 quarts in anyway, without draining the old oil out. She was sure she had broken her car.

Longhair to the rescue! I shut her engine off, and drained out all the oil, replaced the filter, put in new oil, and she was set to go.

Three years later, we were married. In May, we will celebrate the 30th anniversary of that oil change.

Will someone explain how with a positive displcement roots type oil pup that extra oil in the pain will cause high oil pressure?

Oil pressure is not dependent on oil level. Unless, of course, your oil pan is bone dry.

The reason you don’t want to overfill is this: If the oil level in the pan is too high, the crankshaft will come in contact with it. The crankshaft, spinning at over 2000 RPM, will proceed to whip the oil into a foam. This is bad.

As long as this thread is here, I have an oil question perhaps someone can help me with: what’s the difference between, uumm… I forgot the exact numbers and letters but 5-30, 10-40, 5-40, any others?

What should I be using? '94 Hyundai Scoupe that tends to burn oil rather quickly it seems.

Crafter_Man has the correct answer, again.

What if your car has a dry-sump? Do you still have the same problem with over-filling?

The 10W-40, 20W-50, etc. is the American Petroleum Institute’s viscosity rating for the oil. In a nutshell, the 10W- (20W-…) part is a rating of how much oil will pour out of a hole in the bottom of a standardized cup at zero degrees celsius, and the -40 (-50…) part is a rating of how much oil will flow out at 100 degrees celsius. In both cases, lower number mean the oil is thinner.

Use the rated oil in your Hyundai. Using the thickest oil recommended in the manual might reduce consumption. Then again, it may not. The idea is that the thicker oil is less likely to leak through seals, but the difference between high and low viscosity oils isn’t all that great, and most of the oil is probably slipping into the cylinders and getting burned; it isn’t leaking out of the engine. Alternately, you could try using a synthetic oil if you really wanted to shell out the bucks. These typically have higher vapor and flash points, which means that they tend to boil off/burn off less than conventional oils, so less oil is lost.

JKilez, if you overfill the oil tank on a dry sump engine, you run the risk of oil pouring out of the oil tank. The return pump is designed to remove far more oil from the engine than the feed pump could ever introduce.

We could spend from now to eternity arguing about motor oil (a favorite pastime of beer-swill’n men).

Here’s my opinion:

  1. Use whatever viscosity your owner’s manual recommends.
  2. Change your oil and filter every 3000 to 4000 miles.
  3. Don’t worry about brands. Just look for a cheap or “on-sale” oil with an API rating of SH or SJ (or better).
  4. Don’t use synthetic in your car’s engine. It’s a waste of money.

A word about synthetic: While I acknowledge it is a better performer (especially at temperature extremes) over organic blends, I just don’t think the extra cost is warranted. However, I do think it is advantageous to use synthetic oil in air-cooled engines incorporating an oil pump and filter. Being air-cooled, these engines can get pretty toasty, and a synthetic oil will hold up much better. As an example, I have an air-cooled Onan engine on my riding tractor, and I only use synthetic in it.

For air-cooled engines w/o oil filter (e.g. small lawnmower engines), you do not want to use an oil that suspends particulates; instead you want the particulates to sink to the bottom of the engine. Therefore, for these engines you do not want to use oils containing detergents (e.g. blended motor oils designed for automobiles) or synthetic, which also boasts “particulate suspending” characteristics. Instead, use straight/non-blended, non-detergent oil.

The “W” stands for “winter.”

Let me back up… One of the problems with motor oil (or just about any kind of oil, for that matter) is that it has a negative temperature coefficient, i.e. as the temperature increases the viscosity decreases. Problem is, you wish it were the opposite: when starting a cold engine, you would like the oil to be thin, and you would like it to become thicker as the temperature increases. So what would be ideal is a motor oil with a positive temperature coefficient.

As far as I know, know one has figured out how to make a motor oil that has a positive temperature coefficient (fancy blended and synthetic oils not withstanding). Invent one, and you’ll become a billionaire.

So chemists have come up with the next best thing: decrease the slope of the temperature-viscosity curve. This is what blending does.

At cold/winter temperatures, 10W-30 oil has the viscosity that 10-weight oil would have at that same temperature. At engine-operating temperatures, 10W-30 oil has the viscosity that 30-weight oil would have at that same temperature. Another way to think of it: At cold temperatures, the (blended) oil “magically becomes” a 10-weight oil, and at higher temperatures, it “magically becomes” a 30-weight oil. (This paragraph is the key to it all.)

Does this mean that 10W-30 oil is thinner at cold temperatures and thicker at warmer temperatures? No. The viscosity of 10-weight oil at cold/winter temperatures is still higher than 30-weight oil at engine operating temperature. But, this is better than using straight 10-weight or straight 30 weight oil. The former would be too thin at engine-operating temperature, and the latter would be too thick at cold temperatures. In other words, the viscosity vs. temperature curve is too steep for either of these, and blending them reduces the slope.

How do you get just a quart of oil out? If you open the drain plug, swoooooooosh!

Clearly, I can’t, and I must plead guilty to passing on misinformation with my previous post. :frowning:

That said, neither can I explain why it wouldn’t cause high oil pressure. I’m not finding the term “positive displacement roots type” self-explanatory. Can you or somebody else help me out?

Not sure if roots is the correct term for a gear type oil pump but it’s similar to a roots type supercharger.

Anyhoo, positive displacement means that aside from leakage within the pump it has the same amount of throughput per revolution no matter what the speed. Other types of pumps need a minimum speed. A turbine pump for example doesn’t pump anyting if it’s spinning too slowly. A positive displacement pump should not be sensitive to oil level as long as it’s not so low the pickup tube is sucking air.

Overfilling a dry sump engine can be particularly dangerous to the engine (depending on its configuration).

If the sump completely fills to capacity, the excess oil is going to back in place that it should not be sitting in large quantities.

In all engines the risk to the engine is determined by how overfull the engine is.

A little overfull “usually” isn’t too big a deal, as it will usually cause some of the bottom end parts (crankshaft and rods) to slog through an oil bath.

Extreme overfilling can break blocks, rods, and crankshafts. This doesn’t usually happen until the oil is deep enough that it reaches the bottom of the cylinders.

I have personally seen one engine block split out the side due to gross over filling of oil.

But, back to original question (quoted), dry sump engines typically don’t have much room for oil to accumulate outside of the sump where it would not be dangerous to the engine.

The old Porsche 911 is a classic example. It was dry sump. With the horizontally opposed engine, any large accumulation of oil in the crankcase would begin entering the bottom of the cylinders quickly and interfering with piston movement.

Oil does not compress and huge pressures are easy to obtain trying to move large quantities of oil around quickly.

Thanks all for allowing me to hijack in my own questions. So as I understand it, it is not recommended for me to use higher numbers to slow down the rate at which my engine burns oil?