Joe Abbin is a mechanical engineer with over 50 years of experience in analyzing, testing, and racing high-performance vehicles of all kinds. His fascination with Ford Flatheads led him to found Roadrunner Engineering and do a monumental amount of experimentation with these engines, all of which he has documented with scientific accuracy.

We asked Joe to comment on Flathead oil filters.

Thoughts on Flathead Ford Oil Filtration
By Joe Abbin

Every engine benefits from clean oil! A major requirement to provide clean oil is an oil filter. Ford was slow to provide a real oil filter for the Flathead V-8. One did not become available until 1936, when an early design oil filter was offered as a dealer-installed accessory. It was recommended for service in dusty areas. The most commonly seen Flathead oil filter with a replaceable element first became available as an accessory in 1940 and later as standard equipment in 1946. These units were commonly retrofitted on earlier engines for longer engine life.

The stock filter does not filter all the oil, all the time. Most of the oil pump output goes to the engine without filtering and the remainder goes to the oil filter in a parallel flow arrangement. While 100 percent of the oil is not filtered in one pass, the stock filter is effective nevertheless, filtering all of the oil in about five minutes at highway speeds. Various options for converting to full-flow or other systems, which filter more of the oil more of the time, in my view is not generally worth the effort.

How much oil does the Ford Flathead oil pump circulate and how much gets filtered?

The stock Flathead oil pump is a positive displacement gear type, capable of circulating about 15 quarts per minute under ideal conditions when the engine is spinning at 2,000 rpm (the high-volume version pumps approximately 20 percent more). A recent test at Roadrunner Engineering demonstrated that a stock ’46-53 oil filter with restrictor flows about a quart and a half of oil per minute through a clean filter under meaningful conditions of oil pressure (55 psi), temperature (180 degrees F), and viscosity (15W-40). This means that about 10 percent of the oil pumped by the stock pump goes through the filter under these conditions and the rest goes unfiltered to the engine. Therefore, under these same conditions, I estimate that all the oil in a 5- or 6-quart system is filtered in less than five minutes at highway speeds. Not bad and certainly worthwhile!

Additional notes/ cautions

When using the stock oil filter system, it is important to retain the oil restrictor at the inlet to the filter canister. This is a brass fitting with about a 0.060-inch-diameter hole to prevent too much flow through the filter, particularly if the filter element is not installed (ouch!). The Eaton/Weatherhead catalog still shows a similar part available under catalog number 1215. The ’49-53 engines incorporated the restrictor into a tee fitting (8CM-6073 or 1BA-6073) that also mounted the oil pressure sending.

With any type of full-flow conversion, a filter cartridge designed for full flow or a bypass loop must be installed for adequate oiling. No oil flows if the filter inlet/outlet lines are simply plugged. Also, a stock parallel flow-type filter system or beehive type that uses a stock-type filter cartridge will not flow enough oil for a full-flow conversion and will result in almost instant engine destruction.

For additional Flathead Ford building tips get a copy of Joe’s latest book, 335 HP Flathead Ford V-8 Performance Handbook available on the Roadrunner website.

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