Optimum oil level=less resistance

[EdKiefer]

http://www.youtube.com/watch?v=87VAc...eature=related

[some_other_dave]

I didn't watch the video, but I wanted to answer a few questions with facts, and with opinions.

First, dry sump lubrication. This is not used in most cars because it is complex, expensive, and not required. A dry sump system uses at least two oil pumps, one to scavenge the oil sump to a tank, and one to provide pressure to the oil system by pushing oil from that tank into it. Most have more than that, with multiple pumps in the sump or from the cylinder head(s). I believe that the latest-generation Porsche 911 Turbo uses one pump for each bank of heads, and two for the sump--but I could be wrong.

More pumps == more parasitic drain == lower fuel economy. But very little oil in the sump == less loss due to windage == more MPG. Both numbers are very very small, but generally driving the pumps is the dominant factor there.

Race cars and wannabe race cars do it so that they don't lose oil pressure when undergoing substantial G-loadings for longish periods of time. Like long sweeping corners. It's not worth the expense or complexity for most street cars.


Oil levels: A smaller amount of oil will get up to operating temperature more quickly. If there is a decent oil cooling system, particularly one that is thermostatically controlled (or exposed to a thermo-controlled heat sink, such as engine coolant), the oil will stay at the correct operating temperature and not overheat.

A faster oil warm-up means a faster engine warm-up, which improves fuel economy each warm-up cycle.

I have heard anecdotally that having less oil in the sump means the oil is easier to pump through the engine resulting in better fuel economy, but I do not buy that.

Note that engines that are primarily cooled by engine oil (and direct air flow) can be more sensitive to oil condition and temperature than conventional water-cooled engines. I do not think that the motorcycle experience cited above directly translates, except to old Corvairs and a number of old European cars (VWs, Porsches, and a lesser number of others).


Oil light and gauges: The oil light on your car does not mean the oil level is low. It means that the engine has already lost oil pressure (most of them come on at 7 PSI or even lower, which is less than your engine needs for just about any mode of operation) and that you need to pull over right now and figure out what is wrong and fix it! The loss of pressure could be due to a low oil level, but it could be other things.

The temperature gauges in almost all of our cars only measures coolant temp--that radiator fluid stuff. The oil temp will have no measurable effect on that unless you have a water-to-oil cooler, which is not that common, and even then it will generally be a small effect, difficult or impossible to notice on the notoriously insensitive stock gauges.

The stock gauges and lights on our cars should not be regarded as measuring instruments, but more as "HOLY CRAP SOMETHING BAD HAS HAPPENED" indications.

-soD

[autoteach]

if you want to run lower oil levels, go with a larger oil filter and an oil cooler. you can then run it lower down the dipstick.

[C3H8]

Originally Posted by Arragonis

I think it is now because of cats. If you overfill the excess oil is blown out via the relief valve and vents via the exhaust where it gets into the cat and basically knackers it. My TDI Fabia has stickers all over the place warning about this as did my petrol FIAT Bravo and Ford Mondeo.

I hate cats. And I hate catalytic converters.

What are you talking about? what relief valve is there for excess oil that dumps it anywhere but right back into the oil pan? The oil pump and oil filter are the only things with relief valves in the oiling system. And they dump excess oil right back into the oil pan, to be re used again. Do you mean the positive crankcase vent? "pcv"?

and how does excess oil get dumped right into the exhaust? The pcv system routes oil vapours into the intake manifold to be burned by the engine. It does not dump into the exhaust. least not on any street cars i have ever seen. I have seen a few drag strip cars do that. So far as i know we are not talking about drag race cars though, we are talking about economy type cars.

[EdKiefer]

I would recommend just keeping oil level in the middle of two lines which on most cars would be 1/2 qt low of max. For sure you don't want to overfill .
Each engine is different as to how low pickup is to pan bottom and how much baffling it has to give min amount , not worth it IMO, don't let it go below min mark is safest bet

I only posted vid to show how much extra HP they got out of it with lower oil levels , not that I would tell anyone to run like that ..

[comptiger5000]

C3H8 - I would assume he was referring to the PCV valve. And even if it's burned first, the oil can still hurt the cats.

[Arragonis]

Originally Posted by C3H8

What are you talking about?

I could be talking about the PCV. But overfilling does end up with it knackering the cat somewhere if you overfill, which is good to avoid no ?

[SuperHatch]

Originally Posted by C3H8

What are you talking about? what relief valve is there for excess oil that dumps it anywhere but right back into the oil pan? The oil pump and oil filter are the only things with relief valves in the oiling system. And they dump excess oil right back into the oil pan, to be re used again. Do you mean the positive crankcase vent? "pcv"?

The relief valve in the pump dumps the excess oil back into the pan.

The relief valve in the filter simply allows the pressurized oil from the pump to bypass the filtration media, but it is still pumped through the engine. This is a safety feature to prevent oil starvation due to clogged filters. Dirty oil getting to the engine is better than no oil at all.



Other than that I have to agree with everything else you've stated in this thread.

[Laurentiu]

Ok, I want to ask you guys something, don't want to open a new topic on that. This small car of mine takes 3.8 liters of oil (~1 gallon) Normally I would fill up to the max but not it's just below, on the starting point between Max and 1.0L ( it goes like MIN-1.0L-MAX)
I've read opinions here about it being better to put less oil...Another aspect I want to discuss about is the condensation and consequent water in oil which is definitely not good for the engine and for the oil itself shortening its life.

So what I'm thinking, by using less oil > the oil should heat up faster > take less time to evaporate the water that might be in the oil. Is that reasoning right ? Please correct me if not.
The thing is I have a shortish commute now...6-7 miles and even though it's very hot in Cyprus most of the time, I don't think the oil gets to "water evaporation" temperature.
By the way, the engine being small, it does get hot quickly (85-90) but the fan rarely kicks on, just the times when the traffic gets stuck. My only long drive nowadays is going shopping once a week to a supermarket 8-10 miles away and the occasional trip around the island once in a blue moon

So, what do you think ? I would like to test the oil maybe sometimes to see if my 5-6000Km oil changing routine is too soon or too late (I've been using semi-synthetic Mobil 1 10W-40) but here in Cyprus I wouldn't even know how to explain to somebody at the garage how to get that. Last time I asked for directions to get to a clinical laboratory for some tests they've sent me to a barber's shop (I don't speak Greek)

[cfg83]

Frank -

Originally Posted by Frank Lee

...

In fact I have read from the manufacturer that they do NOT recommend always topping off to the full line. Their position is to NOT add until the level drops down to the ADD line.

Now, one possible reason for rock's observation is that when at the full line his engine has what is called windage, which is caused by the crankshaft physically dipping into the oil and whipping it around. Windage is bad not only because it takes horsepower; it whips the oil into an aeriated froth which then does not do as good a job at providing a lubricating film.

Go ahead and run it down to the add line. Or even start things off at the add line. It is possible to successfully run engines below the add line too as the drag racers have found out but for peace of mind I wouldn't go there.

That's basically what I do. When it gets to the Add line I add 1/2 quart, which gets it 1/2 way up. I have an internal timing-chain that is supposed to last a lifetime (not a timing belt). If it gets dry in there the engine-oil-lubricated timing-chain can fail. Since I have an interference engine, a broken timing chain means a lot of smashed valves. That's not a good thing.

On average I think I add about 1/2 quart for every 1500 miles.

CarloSW2