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Too much engine oil. What's the risk?

rmcphearson

Hot Rolled
Joined
Jan 12, 2008
Location
Rochester, NY
I've been told that an engine oil level that's too high can be catastrophic. I don't doubt it. But why? What exactly would happen? I even have a theory based on experience (which I will recount in a later post). But I'd like to hear from you guys first.

Thanks
-Roland
 
Reminds me when the curved part of the dipstick tube rusted out on my ford explorer and I was bamboozled when checking and trying to top up oil before a long trip. after adding 3 or 4 quarts with no sign of oil on the stick I looked deeper into what was going on, it ran fine a few quarts high.
 
I had a diesel generator runaway once because I overfilled the crankcase. Scared the crap out of me.

Shutting off the fuel did nothing- it was blowing past the PCV and running on the crankcase oil.

Killed it by blocking the air intake with a rubber boot.

It made such a huge cloud of smoke that the fire department showed up. :eek:
 
Hydraulic compression on the piston downstroke can make it impossible for the starter motor to turn the engine over (like hydrolock in reverse). I found this symptom useful when a lawn tractor started having difficulty starting. Felt like it was under abnormal load as it was cranking.

As others have said, oil below the cylinders acting as an incompressible fluid can blow out seals and otherwise damage parts that were never meant to be under hydraulic pressure.
 
Years ago I over filled an '88 F-150 with the 4.9L straight six, after a few hours the oil pan gasket blew out and drenched the CAT with oil; I thought the truck was on fire. :willy_nilly:

I was lucky it did because I was young and dumb and probably wouldn't have noticed it until the engine locked up.

Then it took me 8hrs to install a new one piece oil pan gasket because I had to weave it between the crank and pan by feel.

I'm extra careful now when I change my oil.
 
Years ago I over filled an '88 F-150 with the 4.9L straight six, after a few hours the oil pan gasket blew out and drenched the CAT with oil; I thought the truck was on fire. :willy_nilly:

I was lucky it did because I was young and dumb and probably wouldn't have noticed it until the engine locked up.

Then it took me 8hrs to install a new one piece oil pan gasket because I had to weave it between the crank and pan by feel.

I'm extra careful now when I change my oil.

Yabutt..what about the CAT ????....:D

Did you use Dawn Dishwashing Detergent like in the commercials ?
 
I can tell you from an experience last week that if you overfill a 125cc high millage engine it can blow the head gasket. My 2016 Yamaha MIO scooter has just over 40k miles on it and finally took a dump thanks to the Yamaha tech putting too much oil in it. The Yamaha scooters don't have oil filters so I go to the Yamaha dealer every 1000 miles. I buy 1000 ML bottle of Yamalube and the oil change runs 100 pesos ($.85 cents).

When the guy brought my scooter around I ask where the left over oil was, He looks at me puzzled and said "Its in the scooter". I pointed out the label that says 700 ML max. Hes proceeds in trying to tell me that the scooter I have has the heavy duty engine and the label is wrong. Finally after about 20 minutes of dicking around thinking maybe they are smart enough to drain some back out I just said Fk it ill go somewhere else. It was only when My calf gets a dose of hot oil spatter :eek: the math occurred to me. I was thinking "well, its only 300 ml too much". But the hot oil treatment made me realize that was 30% more and the engine has 25k more miles on it than designed for.

I figure it created too much crankcase pressure and blew past the rings then took the path of least resistance from there.
 
This guy has a bit of experience. Probably one of my all-time favorite /r/motorcycles stories: "I put 7 quarts of oil in my bike and that was clearly too much so I drained it and arbitrarily put 2 in. Is it broken?"

I feel bad for the bike, I have the exact same one. They're bulletproof if you...don't do what this guy did.
 
On a modern GDI engine... bad bad stuff. Older engines drain off the excess and move on with your day. One time my friend drained his transmission, double filled his engine with oil and drove his car for a week (Subaru)...
 
Thanks guys. Sounds like several different bad things can happen. Here is my experience from many years ago:
We had two golf car engines (I wanna say 8hp or so Robin) throw rods the same day. They had been filled with hydraulic oil. My theory was since hyd oil expands, the level rose higher than the midpoint of the bottom ball of the crankshaft bearings, then the oil began to churn and turned to foam. And an oil pump won't pump foam.

Anyone agree that's probably what happened?
 
most power generators have an oil pressure switch which shuts the engine down w/no oil pressure. from experience with customer's generators filling around a quart over will shut it down also because of the air bubbles creating from the crank churning it up.
 








 
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