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This is basically show the black parts of a GMC270. If you look you can see a tag hanging from the dipstick tube. Its not a DUKW motor as the distributor shielding is not present.

From the photo there are some solid conclusions that can be made about what parts are black:

Starter
Distributor
Fan
Oil Filter straps
The PCV fill cap and filter AND the support bracket half way down the fill tube. BUT NOT the fill tube. That is interesting.
The coolant pipe from the water pump to the radiator (bottom) appears to be unpainted metal.

I don't know what to make of the different shading of the oil pans.

You questioned the color difference on the oil pan. I am not sure if the oil pan was painted at all. I have two trucks dated 11/43 and 1/44 and neither have any trace of paint on the oil pans. The metal does appear to have had some type of corrosion protection. What is the possibility of them being galvanized? Could they have been field refits from one piece pans to the deep sump two piece pan?

There was an FSMWOs for the conversion from shallow to deep sump for truck not equipped with one from the factory. SSL-1217 "Deep Sump Oil Pan and Oil Cleaner Installation". They most likely (again, this is a guess) would be painted OD. Few if any parts from supply were painted the GMC Olive as they were at the factory.

The FSMWO was to be applied as soon as practical. Usually when the engine was rebuilt.

If you read the GMC Service Bulletin G-61 Step 9:

"Paint oil pan and apply Decalcomanias"

The red/white caution decalcomania PN is 2190260.

Since 4th and 5th echelon units would not have access to the GMC Olive as applied at the factory, and the SSL-1217 did not supply any paint, the only color left would be OD.

So could a FACTORY truck have an unpainted deep sump oil pan? No. Could a field mod truck have an unpainted oil pan? Yes.

If your engine SN is 270-266551or AFTER, or your frame SN is is 220521 or after, or if your truck has the model 3020 engine, then it should be GMC 'Wet Olive' unless repaired/replaced. There would be other ways to determine if the pan was original or a field mod... but these are the 'book numbers'.

TIP: When I speak of CCKWs I ALWAYS refer to the factory configuration. There simply is no way to tell what happens to a truck once in service.

Thanks for the info. My truck is after those serial numbers (frame 298539-B2) and and the two engines I have are 270442893 (removed from the truck listed). This engine is clearly the wet olive and had the unpainted pan. It is a European return so it is very possible that the pan was damaged and replaced at some time with an unpainted one. The second engine is serial 27072594I (yes that is an "i" at the end, not sure why).

On a second note both of my engines support the theory that the oil fill tube was unpainted. The coating on the 270442893 engine still have some sheen left leading one to believe it may have been some zinc or lead anti corrosion coating. The filler and breather are both clearly black as has already been noted.

Until a color photo is obtained I cannot see why thy oil fill tube would not be engine color. No other part of the factory engine is unpainted. I had first heard about the possibility of it being 'terne plated' (which is a mix of lead and tin, like a plating) this year but was never shown any supporting evidence. And there is no reason to put that one part (the fill tube) though a plating process when paint would be more than adequate.

If you think the fill tube is tern plated, I have advocated this simple test: Go to a hardware and get a lead paint detector (it looks like a crayon). Scratch a small part and test for lead. Terne plating is up to 90% lead... if it comes back as indicating lead, then I am open to more discussion. Tern plating is still used today, but uses zinc, not lead... I think its called Terne 2 plating.

This is a good shot of a oil fill tube:



Clearly its painted, but black or GMC Olive is difficult (well, impossible) to tell. But the wear by the cap seems to show that paint is missing.... no matter what the color.

IIRC this is from Jun 1942 in Kentucky.. the photo caption is:

Fort Knox. Negro mechanics. A good ignition job on an army truck. This Negro soldier, who serves as truck driver and mechanic at Fort Knox, Kentucky, plays an important part in keeping army transport fleets in operation

This photo offers a little more contrast.

Note the lower radiator tube. You can clearly see that this is a bare metal part.

Look just aft of the oil filter to the oil fill tube..... its not as 'bright' as the radiator tube:



Again, can't tell color for squat. But comparing what is a known color (the radiator tube) to the oil filter does give a clue.

As for using your truck for comparison... my view is that there is no way to derive what a factory truck should look like buy looking at an in service vehicle. We know that that engines are repainted, and supply oil filters are black, not gray, and that supply air filters do not have air cleaner decals. Its possible that an oil fill tube taken from a supply shelf is not painted, or salvaged off another truck and stripped of paint.... or that in Korea or NATO service saw a replacement fill tube from a third party, or even made overseas (lots of CCKW parts were make in France... I have two split axles and a hydrovac that clearly say made in France under contract) and they would not use the GMC paint at assembly.

So yes, a 'motorpool' truck could have had pink polkadots on the oil pan and oil fill tube. But does not mean that's what it came with off the factory floor.