Yet another radiator cap thread

[Nero]

Hey all, so I drove my old man's truck into work to dump some metal, and he's blowing radiator fluid everywhere out the cap. It was a new cap when I swung the engine in last October, 7# cap. I tested it with my cap tester, and it's completely failed.

I have a 13# cap that's floating in my toolbox, I'm gonna throw that on to keep me on the road for now, but I'm finding some conflicting info about which cap is OEM size. I've found lots of threads stating BOTH are the factory correct pressure sizes....

My working theory is that a 13# cap is correct, mostly because of my latest adventure I had with my own truck, coolant Temps were hitting 230F a few times. With a 7# cap the boiling point is 233F, so a 7# would be close. 13# would be 251F

I may be wrong, but that's why I'm here askin', what do you all think?

 

[Austin86250]

My truck still have factory rad cap and it’s a 13

 

[Big Bart]

I run a 13# too. Many go down in lbs over time for fear of causing a leak. However as you alluded so does the boiling point. If you think his radiator and head gaskets are pretty solid, I would roll with the 13#. Then just watch closely for a couple weeks to see if it develops any leaks.

I always buy the caps with the pressure release tab on top, then you can safely release pressure and remove when the radiator is hot.

 

[Nero]

I'll probably get one of those red lever caps in the future for it, the engine is new-to-us off Craigslist, previous owner had dropped a new IP/injectors and other stuff into it a year before we got it, it runs like a top. No idea if the heads have ever been off. Still has factory head bolts.

 

[03wr250f]

13 was standard
But yes I have run into that, 7, 13 and 16 I have seen claimed as what was originally equipped.

Personally I run a 13 psi napa house brand which is a rebranded stant cap. They are the most consistent cap I have found.

I even know one guy running a 19 psi cap

 

[Nero]

Most caps I see in the industry is 13 or 16. When I was on the hunt for a cap on Friday I found a 20lb and had to do a double take at it. 19 does seem a bit high, who needs their boiling point that high??

 

[Cubey]

I'll probably get one of those red lever caps in the future for it, the engine is new-to-us off Craigslist, previous owner had dropped a new IP/injectors and other stuff into it a year before we got it, it runs like a top. No idea if the heads have ever been off. Still has factory head bolts.

That's what I have on my E350, rated 13. I started using them after a new standard cap on the 78 Dodge wouldn't seal the radiator properly, instantly leaked with the engine on. The safety kind didn't leak, so I dunno if I just got a dud standard cap or what, but I have used with safety ones since.

The E350's:

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