M37 v PW radiator caps

[Kaegi]

does anyone know it the caps between M37 and Power Wagons are the same?

[just me]

They do, but there are two different caps. One is for a wider notch than the other on the neck.

[Kaegi]

wider notch in the neck? but cap will go on either one?

[just me]

Wide tab won't fit narrow notch neck.

[Kaegi]

what is the pressure rating on the M37 caps?

[isaac_alaska]

Not much, if any, if i remember right. I don't think it's a pressurized system. so the cap basically just keeps the coolant from sloshing out, but doesn't hold back any real pressure

[w30bob]

M37 cap is rated for 4 psi.

bob

[isaac_alaska]

thanks Bob, much more accurate than my answer!

[w30bob]

Hi Isaac,

Don't be so hard on yourself............4 psi is basically nothing!
The only reason I remember that is because there was a discussion on here and it seems the alternate vendor part numbers for the cap in some peoples lists are all 7 psi caps. Does the 3 psi difference really make a difference? Probably not, but it does raise the boiling point of water a bit. But we shouldn't be running straight water for coolant........now should we?

Now what the original cap actually looks like.......that seems to still be a bit of a mystery. If anyone has what they know to be the original radiator cap........please post a pic.

thanks,
bob

[Chris P]

My radiator has a metal tube built in that runs from the filler neck across the top of the radiators and then down the side. So wouldn't that mean that there is no pressure in the system no matter what cap is used? Thus you can use any cap that fits?

I assumed that this opening is why the manual says to only fill the radiator to 2.5 inches from the top of the neck, though I'm still surprised that nothing ever sloshes out of that tube. At least nothing that I've noticed.

[isaac_alaska]

that tube is actually above the sealing point, so as long as the cap is "sealed" nothing will ever reach the tube. if the engine heats to the point that water has to go somewhere (out the cap) that tube is there so that when the seal is breached, any water will exit through the tube rather than spraying out from under the cap in all directions

[Chris P]

Isaac, thanks for the clarification.

[Kaegi]

thanks for the answers. good thread. does anyone carry NOS M37 caps?

[just me]

MWM has them.

[Kaegi]

MWM has them.

thanks