For engine gurus: Why overfilling oil is bad for engine?

[47p2]

I've also tried the pre-measured technique and it usually goes way over or way under the dipstick mark depending on the vehicle in question.

Try it and let us know how you get on, but you have to remember there is always a little old oil left in the galleries that you never get out no matter how long you let it drain

[Adrian E]

Checked my oil level this morning and mine is level with the sticking out bit of plastic above the max mark - I'm guessing a quarter to half a litre above where it should be. That likely to be within acceptable tolerance? Bit annoyed as it was recently serviced

Don't know if it's worth trying to get one of those oil removal pumps down the dipstick tube and pump a bit out?

[M-A8]

Very very interesting guys.
I thought about it several times but never thought it might be so dangerous.
I've just topped up 100ml few days ago and went to check the oil level 10min ago, it was 2-3mm above max.
So I'm doing what you suggested, I cleaned the stick and left it out. Will check the oil level in about 20min to see if the reading is slightly lower.

Thanks

[Adrian E]

If left mine parked for a couple of days with dipstick removed in the garage so nice and level. Figure that's as accurate as it gets. Given it's a litre to get from bottom to top of acceptable level on dipstick it can't be a lot over but I'm tempted to pop to ECP and buy a pump so I can work out exactly how overfilled it is. If it used any between services I wouldn't worry, but it doesn't

[Delboy]

Interesting topic this one,

I'm a hot oil checker, pull into the station after a drive where the oil will be up to temp, fill her up by the time I have pumped 80 ish liters I feel that's plenty of time on a hot engine for the oil to drain back to the pan.

Then I pull the dipstick, on the S8 I have found there's no difference from straight pulled reading and wiping and re dipping so just pull and look these days.

Reason for the hot check imo versus cold is the engine is going to be hot, oil expands a little due to heat, increased volume reduces the air volume in the crankcase and possibly creating more oil vapor to be ingested during combustion cycle and we have all heard of the carbon build up in the fsi engines so would like not to make matters worse.

I know its only a little bit extra when hot but the little drop when cold will make no difference to the engine.

[M-A8]

...sooooo, I've noticed no difference after leaving dipstick out for 35min, still about 2mm above the MAX line.
Would you classify this as a possibly dangerous overfill???
I can't see 2mm being dangerous personally purely because a 2mm mistake is so easy to do and having gaskets blown each time you overfill by 2mm would be mad

[Delboy]

Originally Posted by M-A8

...sooooo, I've noticed no difference after leaving dipstick out for 35min, still about 2mm above the MAX line.
Would you classify this as a possibly dangerous overfill???
I can't see 2mm being dangerous personally purely because a 2mm mistake is so easy to do and having gaskets blown each time you overfill by 2mm would be mad

Wah wah wah, Warning failure imminent, failure imminent Wah wah wah

Only kidding I'm sure 2mm will make no difference Marcin

[Goran]

I find the Audi dipstick annoying too, wiping and dipping can result in weird high readings, sometimes wiping and dipping 2 or 3 times produces a better reading but results in smearing more oil up the tube. Testing when hot can give a lower reading if it hasn't drained enough.
The most annoying thing is trying to see the oil level with fresh oil just after an oil change, its too clean and transparent.

In the past I have resorted to wrapping some old 1mm or 0.7mm solder wire around the metal strip between the plastic stops, the horizontal bars of wrapped wire make the oil level much easier to see. The solder wire is removed immediately after test, you definitely dont want to leave it in there.
I think Audi should have designed the metal strip with deep horizontal groves.

[Adrian E]

If you think the '8 one is bad, you should try the one they supply with the C5 A6, which is all plastic! It's damn near impossible to tell where the level is at any time

I find leaving the dipstick out for a while and checking it once gives a fairly decent reading on the '8 - as soon as you've pulled the dipstick up the tube it's left a residue that'll influence another reading

[jza8]

I always try to fill to middle of the level, no point having it close to max.