“What I Learned Today” With Jeff Smith — Such A Thing As Too Much

You hear all the time in the high-performance world where too much is not enough. While it may be true that there’s no such thing as too much horsepower (we would argue that point), the same doesn’t hold true for your oil level.  It is documented that too much oil in a wet-sump engine will not only hurt oil pressure but kill horsepower as well.

We have seen multiple situations where this is the case. We were on the Westech dyno with a third-party big-block Chevy that we were using for a camshaft test. After warming the engine, Westech’s dyno guru, Steve Brule’, ran it up to peak power at around 6,300 rpm. Everything looked okay except the oil pressure dropped from around 65 psi at 4,000 rpm to roughly 40 psi above 5,000 rpm. Steve asked the engine owner how many quarts of oil he had put in the pan.

The owner responded that the oil pan called for 7 quarts so he added an extra “just to be safe”. Steve explained that the drop in oil pressure was directly caused by excessive windage in the pan from the greater volume of oil. Windage causes the oil to quickly foam, which adds air to the oil. When the oil pump squeezes the oil, the air compresses and the oil pressure drops. We drained 1.5 quarts from the engine and the oil pressure stabilized throughout the next two dyno runs to establish an accurate baseline.

oil level

Many steps are taken to minimize windage in the crankcase, but one of the easiest steps is to only use the proper amount of oil in your engine.

We didn’t record the change in horsepower in that particular episode, but in another case, a big-block Chevy suffered from an inaccurate dipstick. Someone added oil until the dipstick read full and then delivered the engine to Westech. Steve pulled the handle on the first run and noticed the engine seemed down on power and the oil pressure fluctuated badly above 4,000 rpm.

He eventually drained over three quarts of excess oil from the engine before the oil pressure stabilized at higher engine speeds and the power gain was substantial – well in excess of 10 horsepower. After establishing the correct fill level for the engine, Brule’ then fashioned a new dipstick with the correct markings so that the problem would not happen again.

In both cases, Brule drained oil in half-quart sessions until the oil pressure stabilized. In these cases, he was concentrating on stabilizing the oil pressure, especially above 4,500 rpm. A pleasant alternative result was a slight increase in power even when the over-fill was only a single quart. What we have not mentioned yet is that this over-fill will also add a slight amount to oil temperature as well. This would become important in an endurance engine such as a circle track or road race engine where lowering oil temperature requires a significant investment in oil coolers, lines, and fittings.

So even for a basic street engine, it’s best to determine the proper oil level and not exceed it, as this will produce undesired consequences. The beauty of this effort is that the ultimate fix costs nothing to ensure the oil level is correct.

oil level

Too much oil can be detrimental to both power and engine protection. It may take some extra effort to determine the proper oil level, but it’s well worth the effort to do so.

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About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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