As with many things there is a balance that needs to be achieved when it comes to your oil level. We have found that there are two common misconceptions when it comes to oil level. The first misconception is that the more oil the better because you don't want to risk starving your engine. The second misconception is that the lower the oil level the better because you don't want windage in the crankcase that will rob you of power. While both of these concepts are correct, carrying them out to the extreme by just raising and lowering the oil level in a stock oil pan is wrong. This thinking can actual cause more problems then it is supposed to solve.
MORE ISN'T ALWAYS BETTER!
The more oil the better argument is usually based on the fact that your oil level in the pan will be reduced once the engine is running and oil is being pumped into the block. When running at higher RPM this is exacerbated. While the thought process is partially correct, this is usually already calculated in the oil level to begin with. The red herring of this argument is usually a few forum posts that tell of oil pressure problems that were experienced on a certain track which after overfilling the engine went away.....at least for that particular racer at that track.
These situations seem to give credibility to the argument but do not provide the entire picture of what is happening in the motor. It is possible the oil volume had been miscalculated to begin with and adding more oil simply made up for that miscalculation. Or perhaps something with the pan or oil pickup was not functioning properly and the extra oil was working to cover up that issue. In either case running too much oil has its own drawbacks that you will want to be aware of.
See "the science of oil slosh" blog post for more on how oil moves in the pan.
There are a few things that happen when you have too much oil in your oil pan. The first thing that happens is that it will create windage. Windage is a term that describes the turbulent environment that is created in the crankcase as oil spray mixes with the air flow churning under the pistons and around the crank. Windage creates a parasitic draw on an engine's power. It is a hurricane of oil and air that can cause unnecessary strain on your engine. The analogy that we like to use is walking through a pool and walking next to the pool. The amount of effort that needs to be expended to move the same distance is substantially different depending on which path you are taking.
The second major thing that can happen with too much oil in your pan is high oil temperatures. You might think that the more oil you have in your system the cooler the oil will be. Well, that is correct, but only if you have a pan that gives you the room for that extra oil. When the extra oil in the system approaches the crank the result can actually be higher oil temperatures. That extra oil ends up splashing around the crank and under the pistons creating windage. Windage can cause aeration in the oil which reduces the oils ability to pull heat from the engine. Even though modern oils have anti-foaming agents that aim to reduce the underling cause of foaming, the high amount of windage makes the oil more vulnerable to it. For more information on the role of oil and additives in performance, see our e-book "Why Engine Oil Matters to You".
MAKE SURE YOU HAVE ENOUGH
Of course we all know that not enough oil can also have a negative affect on your engine. This can be anything from running too hot to not having the oil pressure needed to prevent engine damage. We frequently see a low oil capacity strategy implemented by drag racers that are trying to maximize their power. In drag racing the smallest improvement can show up on the ET slip. The obvious problem with this is the risk of damaging your engine.
What may not be as obvious is that not all potentially damaging drops in oil pressure are noticeable without moment by moment data acquisition. Quick dips in pressure on the dashboard gauge will be rarely noticed by the driver that is negotiating the exit of a fast corner. Those moments of pressure loss can accumulate lap after lap and set the stage for substantial engine damage.
Frequently racers use oil accumulators to give them the safety net to run the system low on oil. However, we typically discourage using an accumulator as part of your primary oiling source. For more information on Accumulators check out our blog series here.
HOW DO YOU BALANCE?
The balancing act in your oil pan typically starts with the manufacturer's suggested level. From there anything added to your oiling system is in addition to that oil capacity. For instance, an added oil cooler will need to be calculated into the final total. Everything from the lines and fittings to the cooler need to be calculated. The easiest way to accurately measure this is simply utilizing your dipstick. First, make sure your dipstick is calibrated correctly for the manufacture's suggested oil level before adding on or filling the components. Next, add your best guess as to the amount of extra oil required, with the understanding that it is easier to add oil then to remove it. After adding the oil, run the motor for a minute in order to fill the added oiling components. Turn the engine off, then check and fill to the dipstick mark.
There are a few circumstances that can require your oiling system to be adjusted. These things include but are not limited to oil pump volume, engine oiling passage tolerances, motor stroke etc. Yes, even motor stroke. The best example of a way oil level can unexpectedly affect an engine is a longer stroke motor. In a stroker motor the counterweights on the crank go deeper into the pan. This requires a slightly lower oil level compared to the original oil pan capacity. Without this adjustment you can create windage in your engine.
When determining your oil level there are a few things to look out for when trying to find the right balance. The first is oil pressure drops. This symptom unfortunately can show up in both over filled and under filled situations. In an over filled situation the oil will typically be frothed up by the crank to the point where your oil pickup will start sucking up air bubbles and creating gaps in oil pressure. If your oil pan is under filled it can cause oil pressure problems in two different ways. The first is under cornering, braking or acceleration the oil will run away from the pickup and the pickup won't have any oil to pump. The second is if the oil is not able to drain out of the heads fast enough to keep up with the oil pump.
Another symptom of oil level problems is the oil temperature. As with oil pressure problems the oil temperature is affected both by the oil being too low or too high. As mentioned above, in an over filled situation the oil will heat up fast as it is continuously splashed on the crank and cylinder walls. In an under filled engine the oil temp will rise slower but will still get too hot as the capacity of oil is not able to dissipate the heat fast enough. This happens because each quart of oil is being run through the engine more frequently then it would be if there were more. Consider running a relay race in which one team has 5 runners and one team has 10 runners. The team with 10 runners will stay fresher because they have a longer rest period.
Despite the challenges in finding the right oil level balance the rewards can be very worthwhile. If you can strike the right balance you will find that you can maximize power and minimize the possibility of damage being done to your motor which is the ideal situation. A great illustration of this is an experiment that Hotrod.com did in which they blew up a SBC engine. The test run showed the engine at 298hp. After the oil was drained and run it put out 307hp. The problem is that it eventually threw 2 rods. That video can be found here: http://www.hotrod.com/articles/what-happens-when-you-run-an-engine-out-of-oil-it-explodes-wheel-of-death-vol-1-is-here/
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