# How does too much oil hurt the cat.?



## frateretto (Dec 19, 2008)

Just curious, as to what actually causes the potential cat. issues - and how for over the capacity does it take to cause damage? An extra 10% causes troubles etc? 
Thanks,


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## rajvosa71000 (Jun 9, 2004)

*Re: How does too much oil hurt the cat.? (frateretto)*

Why are you worried about too much oil in your engine at the first place?
I mean, are you planning to put more oil in it than it really needs it? why do that?
Too much oil would end up going through your intake sistem via crank case breather, and eventualy clog up your CAT...since the oil is hot, it might evne burn it up.
That's at least my theory


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## frateretto (Dec 19, 2008)

*Re: How does too much oil hurt the cat.? (rajvosa71000)*

not really looking to add more for the fun of it .... gf put too much oil in the car (jug slipped, filled funnel) ... and I need to suck it out, just curious as to what it would actually do the car. 
Also was looking for some level of urgency (how much over-filling does it take to hurt) so I can decide whether I need to do it immediately or if it can wait a day or two.


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## BuddyWh (Nov 11, 2006)

*Re: How does too much oil hurt the cat.? (frateretto)*

From what I've always been told: too much oil means the level could come in contact with the crank which can 'whip' the oil into a froth leading to loss of oil pressure which is kinda bad for bearings.
But to answer your question about the cat: excess oil can also blow through the PVC and be burned at very high rate, leading to poisoning of the cat. You can read the whole article in Wikipedia, but here's the important part:

_Quote, originally posted by *Wikipedia* »_Poisoning...
Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing substances that coat the working surfaces, encapsulating the catalyst so that it cannot contact and treat the exhaust. The most notable contaminant is lead, so vehicles equipped with catalytic converters can only be run on unleaded gasoline. Other common catalyst poisons include manganese primarily from the gasoline additive MMT, and silicon which can enter the exhaust stream if the engine has a leak allowing coolant into the combustion chamber. Phosphorus is another catalyst contaminant. Although phosphorus is no longer used in gasoline, it (and zinc, another low-level catalyst contaminant) was until recently widely used in engine oil antiwear additives such as ZDDP. Beginning in 2006, a rapid phaseout of ZDDP in engine oils was begun.
Depending on the contaminant, catalyst poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time. The increased exhaust temperature can sometimes liquefy or sublimate the contaminant, removing it from the catalytic surface. However, removal of lead deposits in this manner is usually not possible due to lead's high boiling point.

Meltdown
Any condition that causes abnormally high levels of unburned hydrocarbons — raw or partially-burnt fuel — to reach the converter will tend to significantly elevate its temperature, bringing the risk of a meltdown of the substrate and resultant catalytic deactivation and severe exhaust restriction. Vehicles equipped with OBD-II diagnostic systems are designed to alert the driver of a misfire condition, along with other malfunctions, by means of the "Check Engine" light on the dashboard."

So oils high in zinc, which seem to be real popular here, appear to be the ones most prone to this problem. I've wondered if the high-zinc formulations are racing oils and diesel oils, like Rotella T, and therefore aren't part of the 'phase-out' of passenger car motor oils alluded to in the article. Not saying they are bad, but not being optimised for use in gasoline engines, under average use, they don't have to be concerned with this problem nearly so much. 
I would think manufacturers would make allowances for overfilling so there should be some tolerance. Pull the dipstick after running under a light load for a while - if it's milky or frothy then drain some out right away. Otherwise, unless you chronicaly run over-full I'd imagine the cat is safe for a while.
_Modified by BuddyWh at 10:03 AM 7-2-2009_


_Modified by BuddyWh at 10:05 AM 7-2-2009_


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## frateretto (Dec 19, 2008)

*Re: How does too much oil hurt the cat.? (BuddyWh)*

Thanks for the details.
I had checked the dipstick (many times) and all seemed normal with no frothing or milkiness.
Either way, I pumped the extra oil out the other night, so all should be well now. I'll disconnect some of the PCV hoses tonight (maybe) and look for excess oil. The hoses are all new, so in theory they should be clean and clear (right?).
Thanks again for the details - I did do a fair bit of searching, but had not been finding what I was looking for.


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