proper oil for 1940's era aluminum ford engine

Question

I would like to know the proper oil to use in a Ford GAA engine from around 1945. Could be as late as 1958.

From a series of photos of a GAA being restored on Flickr.

Currently this engine has all the original seals and gaskets and showed no signs of leaking when I got it.

I do know the bearings are silver babbitted and the block, heads, and covers are aluminum. It has brass cam gears and a gearbox upfront to run the magnetos water pump PTO shafts and cam drive shafts.

I am thinking this is going to be a pretty heavy oil maybe a straight 50 weight or something but not sure. I have not found any parts list that has a part number specifically for this engines oil. I do have a copy of the GAA / GAF / GAN service manual but any other documentation would be great.

Answer 1

Per @Eric Urban's suggestion,

I found the Technical Manual for the M4A3 tank published in 1942. That tank did use the aluminum Ford GAA 18L V8 engine which produces 500 hp at 2600 RPM!

It says:

Capacity: 32 Quarts

Above 32°: SAE 30

32° to 10°: SAE 30 or 10

10° to -10°: SAE 10

Below -10° : Not Listed

Replace the oil every 50 hours or 500 miles on dirt roads or 1000 miles on paved roads. (These are miles in a tank.)

Clean the oil filter every 1000 miles.

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I believe @user23543 has a point that oil formulations have changed over the years.

In 1942, the SAE J300 standard was much different. It was only concerned with one viscosity and tested that in a much different way than today. They used a different test apparatus and different temperatures.

Some say, "the minimum standards for each grade have only become more demanding [over the years]". That's a good general rule, but it's not that simple.

SAE J300 started out measuring just one viscosity of the oil with a "crude" apparatus. Nowadays, SAE J300 prescribes the grades by listing the viscosity under several different conditions.

Today's oils are probably overall better than back then, but since we do not know the other viscosity numbers from back then, we cannot make a full comparison.

I have been unable to find the revision year of SAE J300 that was applicable in 1942. I have also been unable to obtain a copy of the original SAE J300 standard published in 1911.

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The original SAE J300 compared all oils the same; it did not break "oils" up into the various categories we have today.

Illustrative points:

• Prior to 1947, oil was not divided into Regular Type (mineral oil), Premium Type, and Heavy-Duty Type (contains detergents). (source)

• Prior to 1952, oil was not divided into gasoline and diesel engine categories. Even then, that was part of the API standard, not SAE J300. (source)

• In 1952, SAE added the winter ("W") grade. (source)

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The viscosity of SAE 30 back then and the viscosity of SAE 30 now are similar, but not identical.

I have no information on any of the other properties that we take note of today from the oil back then.

SAE 30 is a good starting point though.

Answer 2

Given the changes in oil formulations since the time this beast was built and now, I'd consider a change in the oil. Straight-weight oils as formulated then and now are considerably different.

Were it me running such an engine (and I work with antique engines on a regular basis) I'd be using a 15W40 Diesel oil in it.

Modern oils over the past few years have had the levels of ZDDP (anti-galling agent) reduced in them dramatically - and with a whitemetal bearing engine (not sure of the tappet type - if it's flat-tappet more so) you want the extra lubricity.

In my home shop I stock 15W40 Diesel oil in bulk and all of the engines suited to it get that. The modern hardware my wife drives get the recommended oils, but all of the antiques and my daily driver Diesel get the 15W40.

Answer 3

The Ford GAA was originally manufactured for the M4 tank and other armored vehicles. I recommend finding the maintenance manual from the US Army for one of those vehicles, then working your way forward. You are very unlikely to find the exact oil they specify, but should be able to locate a substitute. Contacting a museum with a running M4 that uses the GAA engine would be a good place to start.

Answer 4

I have a 1929 Vauxhall Cadet, I always use 20W50 in its 6cyl 2.2L engine. It has always run perfectly. Chances are the original oil is not available anymore, or other oils from these days are way better anyway.

That engine looks totally awesome by the way!