Overfilled crankcase = bent conrod?

[Paranoil]

Could over-filling an engine with oil cause a conrod to bend? Assuming that no oil got into the cylinder, and therefore no risk of hydro-lock, could an over-filled crankcase result in a bent conrod?

This is a question from another forum, where an engine allegedly had 7.5 litres of oil in it, instead of 4.5, and this was, according to the dealer, the cause of a bent conrod.

 

[Tosh]

I have no actual experience in this kind of failure, but that would be exactly the damage I would expect: rotating crankshaft hitting oil level would cause damage to the weakest link, the connecting rod.
The animation on this page seems to incorrectly show the crankshaft rod bearings rotating through the oil level in a manner which might cause the damage you are referring to.

Others: Does the crankshaft really run into the oil level like that?

 

[JAG]

That is vastly overfilled so the crank could be "swimming" in the oil and it wouldn't surprise me that if the rpms or torque were high enough that a conrod could bend. Not saying it did, just saying it seems easily within the realm of possibility. Ever crash while jet skiing? Liquid is pretty hard when hit at fast speeds.

 

[JohnBrowning]

Never seen it happen ever and I have seen some insane overfills. Usualy if it is that overly fuel a seal will let go. It is normal practice in Auto-Cross circles to over fill by 1 quart.

 

[JohnBrowning]

I almost forgott to add that my wife once added 3-4 quarts to a car that already had plenty of oil in it. She miss read the dipstick. So her buick had 4.5 quarts in the sump and 3-4 more just for good measure. She drove it 18 miles to work and home like that before I discovered it. No damage but had me nervious as heck though!

 

[OriginHacker21]

As I've stated somewhere here before: Spent 4 months or so working at Wal-Mart's TLE department. Had a guy come in who had us do his oil change but then proceeded to fill the oil up to the top of the oil cap after we got done. According to older employees he's been doing this forever and never had problems. We always made him sign the liability waiver. He says the engine likes the extra oil.

This was Pre-BITOG so all I can remember was: Oldsmobile with 150k on the odo.


Personally, I've always put a little bit above FULL (maybe .3 quarts more) mark. In 3,000 miles it hits the FULL line perfectly.

 

[Louie's gone fishing]

When the piston is going down, if it hit oil the con-rod would be in tension, after the expanding gas was done pushing. I would think that before you got enough oil to cause that kind of failure, the engine would be smoking and with enough oil, quit runnint.

 

[Oldmoparguy1]

Depends on the engine. Didnt hurt my sons's 94 Acclaim 2.5L 4 cyl. He had one of those iffy lube type places change the oil, then drove it for a week. When he stopped by I noticed it was running rough so I popped the hood to look, I saw oil all over the front of the oil pan. Checked the oil and it was way up on the dipstick. Drained the oil and got over 8 quarts out of it. Cleaned everything up and refilled it with 5 quarts of GTX and a new filter. No harm done, but a couple of years later had to redo the oil pan gasket.

 

[Rickey]

It would be a heck of a coincidence to have a rod bent just after overfilling, and with no relationship between the two. What if he overfilled it in an attempt to get rid of a knock due to a bent rod?

If the rod was indeed bent by overfilling it would be the first time I've heard of it. Not to say it is impossible though.

 

[Rickey]

Do they really know that it didn't hydrolock?

 

[JohnBrowning]

If the rod was already knocking then the failure was more then likely mechanical failure. I doubt the oil had anything to do with it. You can only bang a rod against a crankshaft main for so long before something has to break. THe bearing failure was the cause of of the rod knock and the broken rod.

 

[Rickey]

Not to argue with JohnBrowning, he makes a good point. One other possibility occured to me: Detonation from extreme anti-knock reduction of the fuel/air mixture due to the presence of excess oil in the combustion chamber? Sucked in through the PCV system maybe?

 

[another Todd]

I saw a diesel engine once that held 40 qts. After the mechanic changed the oil he refilled it. Twice. It smoked a lot and ran about 80 miles before 10 gallons was drained out to bring it to the correct level. No damage.

 

[mechtech]

There are vents in the inlet and outlet of the PCV system that would relieve the pressure.
A con rod can bend from hydro-locking in the combustion chamber because there is no relief on the compression upstroke.