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Hi Guys,

I keep seeing different gas caps on M37s and I'm curious as to why. Below are pics of 4 that I've seen, 2 vented and 2 not vented.....there may be others. My 52 has it's original cap and it's the non-vented variety with the raised ribs (like a star). Can someone explain why the two varieties (vented and unvented).........I'm a bit confused.

thanks,
bob


NonVented2 by w30bob, on Flickr


NonVented1 by w30bob, on Flickr


Vented2 by w30bob, on Flickr


Vented1 by w30bob, on Flickr

Bob
To my knowledge, the vented cap is the correct one for our trucks. The last two you show are the same cap, only the ears have been broken off of the last one. The pattern for those caps is not unique to the M37. They may have been used on other trucks or equipment, even civilian. I have an antique terrazzo grinder i'm bringing back to life. It has a water tank on it that takes the same cap as our trucks.

Brett

Page 17 of PS Magazine No. 34 (1955) has an illustration of the vented and non-vented gas caps. M-37s require a cap with a pressure relief valve, i.e. vented, unlike Reo/Studebaker 2-1/2 ton trucks, which vent in the tank, not the filler. I'm surprised that those M37s with the non-vented caps run properly.

Interestingly, the image shown in the magazine of the vented cap has the embossed lid with the five ribs, like the photo in w30bob's post of the non-vented cap, so apparently that cap design is not indicative of venting or non-venting. The cap should have embossed lettering, however, that indicates if it is a pressure relief type.

Go here: http://dig.library.vcu.edu/cdm/landingp ... ection/psm to view and download the entire collection of PS Magazines.

Mine is the vented type.

Hi Elwood,

Thanks for the info.....and that's a great link! But now I have to admit..........I'm REALLY confused.

So if I'm getting this straight....there are 2 kinds of caps.....vented or non-vented (ie pressure cap). But the vented caps are "pressure release" so they're really only vented above a certain pressure. I posted this topic because I was bullshitting with Ed (Majorhitt) at the MTA meet the other weekend and he had for sale a number of M series fuel caps. That's where I first saw the manually vented cap like Carter has with the little clip you turn under the cap. I just went out and gave my cap a good look and it doesn't say anything on it. I also went back and looked in the manuals I have regarding preparations for Fording, expecting to find some direction to take off the cap and move the little clip to the "closed" position.........but didn't find any reference to such a cap. And someone posted recently in a reply that the M37 cap was turned to the first click for normal operation, and then to a second click to seal the tank. I haven't read anything related to such a cap either. Ed had mentioned that one time he had an issue where his truck would stop running after a half hour or so.....and it turned out the vent cap was set to "closed".

Now that I've thought about that a bit......and you mentioned that the bigger trucks, unlike the M37, vent in the tank.....I'm confused again. I know, my confusion is getting old.
But from what I read and see in my truck......the M37 also vents in the tank. There's a big vent line that runs from the tank up to the carb intake extension elbow. So I'm not sure why the cap needs to be vented at all, unless it has to do with deep fording.....which doesn't seem to be the case.

Again, thanks for the link, and don't hesitate to set me straight on this topic.

thanks,
bob

Mine is different than all of those and I'm pretty sure it's the original that came with the truck. I'll post a picture tomorrow.
Gary

Well..........I was looking around online, etc, and I was starting to come to the conclusion that the cap with the little thing you twist to vent or unvent (like Carter's) was used primarily on the M35 series of trucks. But then a funny thing happened. At the MTA meet last week I picked up a copy of David Ahl's "Dodge M37 Restoration Guide" for $10 bucks (couldn't pass it up). I'll comment on it in another post, as I've got both good and bad things to say about it........but there's a section in it comprised of reprints of various Army publications. In one of these, from PS Magazine (Preventative Maintenance Monthly), there's a reprint of how to be your own inspector of your M37. It's one of those cartoon types with the hot babes directing the hapless GI. It goes around the truck and points out the things to look for.....and when it gets to the gas cap it says "GAS FILLER CAP - Cap loose, gasket missing, damaged; vent closed (used only for fording), etc, etc".

So my take-away is that the cap with the vent switch thingy (like Carters) was indeed used on the M37. I'm thinking it came later in production, possibly only on the B1 version....but am not sure. ORD 9 only lists one cap, but that pub is dated 1954....so what happened later is a mystery. Anyway, interesting stuff......keep the comments coming.

regards,
bob

Bob; I all M37s I have ever seen have had vented caps and although I have no proof I believe they were factory installed and not put on later by using unit OMS personnel or private owners. I can see no reason they would have been changed since they usually do not fail under normal use and are not a high volume replacement part. The unit's shop would have stocked more than the one allowed under based on TM 9-2320 212 34P, page 44 which permits 1 for a 30 day supply to be carried for replacement of defective ones.

" It's one of those cartoon types with the hot babes directing the hapless GI. It goes around the truck and points out the things to look for. "

I believe her name was Connie Rod or maybe Rodd, had a great figure with perfect hair that was never out of place.

Bob,

I would have to agree with Carters comment about the vented cap.

Bert

Please note that I'm not a gas cap expert or have I ever played one on TV.

" Please note that I'm not a gas cap expert or have I ever played one on TV.

What... not an expert? But you are a moderator and you know everything...

Carter.....you even know the name of the hot cartoon babe! NOW I'm impressed.

regards,
bob

So here is a shot of mine-non vented, likely due to the fact that the tank has a separate vent tube running up to the carb elbow:

w30bob wrote:Carter.....you even know the name of the hot cartoon babe! NOW I'm impressed.

regards,
bob

I always thought her name was an interesting play on the words connecting rod and back in the all male army with a bunch of horney GIs around checking out every good looking girl the options were look at the air brushed honeys in Play Boy kept in the latrine, but you could not stay in there long or gape at Connie in PS Magazine. Something else comes to mind, I believe the square jawed old trooper in the magazine was called Sgt. Halftrack.

Cal_Gary wrote:So here is a shot of mine-non vented, likely due to the fact that the tank has a separate vent tube running up to the carb elbow:

Hey Gary, don't think I ever saw one like that, where do you hook the chain?

Carter wrote:" Please note that I'm not a gas cap expert or have I ever played one on TV.

What... not an expert? But you are a moderator and you know everything...

Carter,

I know Nothing..........................!

Bert