Inlet & outlet appear same as 47 Custom but not the cap. Would anything late 30's early 40's having the upper core support rods have used that type filler?

No, but since Modine is still in the business, have you considered contacting them? Sometimes you get lucky and get a customer service rep willing to go out of his or her way to find info.

Its Modine

AD- 4890L050

Does this help?

Jed, perhaps a better move would be to remove the cooler and pressure check. A local radiator shop could do this for you if need be. In my personal experience with many verities of application from heat exchangers in automobile radiators to industrial heat exchangers in fire engines and commercial applications such as over the road diesel engines have been that the heat exchanger are a weak link, periodically exchanging fluid into fluid.

From what Dave (O_D) has said, this is not the case on Packard V-8 applications. I stand corrected and would strongly recommend before spending the money and not being sure of the true issue, test yours.

Best of luck,
Jim

Thanks everyone for the advice, it's appreciated. Kev, I did check the oil and it looked normal. I don't know if that means I don't have a blown gasket or not. I'll replace the tranny cooler and see if that solves the problem. Max Merrit has them for $225. I'll post the results when I get it done.

Have you checked your transmission and oil dipsticks? If either of them is full of chocolate milk there is your answer, either a bad tranny cooler or blown head gasket.

John - it's all good. It was a good reminder to post to the right category. Somehow I just ended up in that one. Thanks for pointing it out. In the absence of being able to hear a persons voice and tone, I always give people the benefit of good intent Thanks again for taking the time to point me in the right direction - Frank

I still vote for tranny cooler, very failure prone and seems to fit the symptoms.

At least in my own experience and that of other local owners, the transmission cooler is not failure-prone, quite the opposite. But I do agree it would be my #1 candidate for your symptoms.

I seem to recall to contributing with others some time back to a list of suggested spare parts and supplies to take on tours. Maybe it's time to find it and revive the topic?

Normally, there is no direct engine oil pressure in contact with the cooling system except in the earlier 3 piece engines equipped with oil system heat exchangers. I would be highly suspicious of one of those letting go, especially since the newest one is now 71 years old.

That said, Kev has a good point on possible head gasket. There could be some oil pushed in, and would also help explain bubbling from the radiator cap possibly caused by combustion pressure. I still vote for tranny cooler, very failure prone and seems to fit the symptoms.

Let us know what you find.
Jim