Freeze Plug Blowout (Yikes!) Gates 31329 Cap to Blame?

[Heavy Metal]

Today the number four (from the front of the block) freeze plug blew out while I was driving on the highway. My idiot light failed to warn me of the impending disaster (just happened too fast or maybe requires liquid to trigger the thermocouple?), luckily I was able to get my jeep off at an exit just after steam started to make its way through the firewall. Not only was there a NAPA conveniently located across the street from where my truck finally decided to die, but they had a 2" rubber expansion plug in stock and I was able to get it installed from underneath the truck! My luck was unbelievable today. 

 

My question is why did this freeze plug let go like it did? I know that the previous owner had new plugs installed a little under one year ago. I suspect that it is the Gates 31329 coolant reservoir cap that I am running, it has a 20-24 PSI relief valve. Stock is what, 16 PSI?

 

I think that some people here are running the 31329 cap without issues, but maybe this freeze plug was not properly seated, or it had a bad taper, and the additional pressure was just a bit too much for it to handle? 

[Jeep Driver]

I doubt it was the fault of the cap. You'll blow a tank or hose before a freeze plug lets go.  PO did a poor job of it.

[Marine1Texas]

agreed pervious owner did not put it in right. In over 30 years of driving never had a freeze plug burst. I have had hoses and tanks burst never a freeze plug. the pressure that would require to remove a freeze plug at 200 plus degrees is way more then 40 PSI. freeze plugs are as stated, cold makes them shrink, heat makes them expand. I once had a spark plug shoot out because engine got warmer then plug and it was -38 outside.

[yellaheep]

Freeze plugs are fickle girls.........

 

Previous owner could have gotten a little over enthusiastic with the surface prep of the block opening and cleared off too much metal.

 

Previous owner could have installed it in correctly and it was cocked a bit in the block opening keeping it from having been pressed in tight enough.

 

 

 

My bigger concern is that the freeze plugs were changed out by the previous owner because that same one popped out on him too.  Why?  Because the block opening is cracked....... I've experienced this myself.  SUCKS!

 

[jimoshel]

PERMATEX

[Marine1Texas]

permatex I good stuff. I know a guy who used JB cold weld and after it set and hard for a day, he ground it down flat. nothing ever coming out of there lol

[big66440]

PERMATEX

RIght Stuff,,,pricey but best stuff I've ever used.

[Heavy Metal]

When I get some free time I intend to remove the manifolds and replace the rubber plug with a real plug. I will be sure to check the block for cracks, and use a sealant. I have heard mixed things about sealants on the plugs, but it certainly can't hurt.

 

Also, after the truck overheated I thought I had blown the head gasket. It looked like it was weeping fluid from the gasket down the block. Turns out my block is so grimy and oily it was just warm sludge running down the block  :rotfl2:

[yellaheep]

I spray the back and outsides of the freeze plugs with Copper Coat just before install, then let them set up for a couple hours before putting in coolant.  Copper Coat seems to keep the plug metal protected and seals up any small grooves/gouges in the block opening surface.  Figured if it's great on head gaskets, should be great on freeze plugs.  :thumbsup:

[Eagle]

I've always used black Permatex (not RTV) for installing freeze plugs. Never had one pop out.

 

FWIW, the factory pressure cap is 13 psi.

[Heavy Metal]

Hmm, I may return to a factory pressure cap. It seems unwise to run the system at nearly double the pressure it was designed for. Not that it is always in the low twenties during operation, but it gets pretty hot here (Hawaii) and the cooling system in my truck was pretty neglected when I got it.