How Much is too much?

I think we're talking about oil overfill in this case, not fuel overfill.

 

<div class='quotetop'>QUOTE(TonyPSchaefer @ Oct 20 2006, 01:16 PM) [snapback]335626[/snapback]</div>

To stray from the original post a little how can one tell if the carbon filter is damaged as a result of a fuel overfill? I suppose mine probably is toast because a few times I had fuel nozzles not shut off when they should have (even got the infamous burp once). And if it is damaged, other than increased emissions, are there any other problems that might be caused by a damaged carbon filter?

I imagine thousands (if not tens of thousands) of Prius's are probably now sporting damaged carbon filters due to occasional overfilling. It would be difficult to believe this is a problem with most other automobiles. I would assume most automobiles are designed with the proper valves in the vapor lines to prevent backflow to the carbon filter canister. Too bad Toyota could not design the fuel system to prevent damage to the filter as a result of overfilling.

Rick
#4 2006

 

<div class='quotetop'>QUOTE(Gadgety Bourgeois Type @ Oct 20 2006, 02:08 PM) [snapback]335659[/snapback]</div>

I'd always heard the concern with oil overfilling is not a mileage (economy) impact, but increased engine wear or damage due to the crankshaft frothing the oil into a foam, which has poor lubricating qualities. I guess increased friction in the engine could result in lower mileage, but I'd more concerned about the engine.

I've never had good luck unscrewing a drain plug and letting just a little oil out. Your best bet might be to remove the oil filter and pour out the contents, depending on how much it's overfilled.

 

basically, 1/4 inch is nothing. if you're really picky and want to spend some more time at the dealer you could bring it back.

lots of discussion of this here

but i'm gonna cheat and just copy one of my posts from that thread here:

excess oil will return through te PCV system into the intake, and what gets into through the air intake will be burned with the gas, which isn't so hot for mpg, and what doesn't get carried with the air into the cylinders gets pooled in the bottom of the air intake. modern air intake manifolds are designed to direct airflow in a certain manner. the oil in the intake changes the airflow pattern, changing how well the gas is dispersed.

as far as oil overfill relates to pressure inside the engine, it's known that increased pressure inside the crankcase wouldn't affect mpg. extra oil inside the engine cannot physically restrict engine operation. it would, however, affect the oil leak situation. (blown out seals from too much pressure and in extreme situations, oil blowing past valve seals)

 

<div class='quotetop'>QUOTE(Gadgety Bourgeois Type @ Oct 20 2006, 02:26 PM) [snapback]335672[/snapback]</div>

As galaxee says, 1/8 to 1/4 inch over is probably not a big deal. At some point though, overfill too much and the oil will be in contact with the crankshaft. Not good. I'd have thought half a quart over would be much higher on the dispstick, so they probably just "eyeballed" the last half quart.

 

<div class='quotetop'>QUOTE(Gadgety Bourgeois Type @ Oct 20 2006, 02:50 PM) [snapback]335697[/snapback]</div>

No, I meant "measured by eye". When I change oil, I put 3.25 quarts or whatever in, then start the car, etc., check oil, add some more to get it just under the full mark... That takes more time and effort, but gets it "just right". Can you tell I am picky? If I were in a hurry, I'd just pour in 3.5 quarts (going by the marks on the side of the bottles, and probably end up a tad over as the engine doesn't always drain completely.

 

There's no need to get it right up to the FULL mark. Put the level at about halfway between ADD in FULL by pouring in three quarts, and worry not.

 

<div class='quotetop'>QUOTE(richard schumacher @ Oct 20 2006, 04:19 PM) [snapback]335802[/snapback]</div>

I did say I was picky, or as they say here in Raleigh, "particular." I usually aim for 1/8 below full, actually.

 

AFAIK no one has yet measured the dipstick marks compared to height of the crankshaft components, with the Prius oil pan cover off.

In 2001 Prius, I can confirm that a small amount of engine oil acculumates in the intake manifold even with the engine oil level 1/4 inch below the 'top full' mark. Guessing that the camshaft chain is throwing oil droplets into the top valve area, which then get passed out the PCV valve. In other words there may be some potential for 'oil frothing' even when oil is not overfilled.

Various Prius groups have many observations of apparent reduced fuel economy with overfilled oil, but it is not so easy to attribute a particular mpg to a particular factor. Seems to me that the jury is still out, but there is no perceived benefit to any amount of overfill.