I've had a Supermiata crossflow radiator in my car for a few years now. I went to drain the coolant and noticed the seals on the two drain plugs have degraded and are leaking. I can't find a replacement online. Has anyone dealt with this before?

Right now i am just debating on sticking an o-ring in there.

 

A 3/8” bonded sealing washer (metal-backed rubber washer) works really well and is sold at any hardware store. Unlike a regular rubber washer or crush washer, they grip the bolt/plug tightly to provide a radial seal, and they are meant to seal well with minimal torque.

An O-ring won’t seal as well under the head of the bolt since it’s not designed to be squished like that. A normal copper crush washer will need a lot more torque on a plug that’s comically easy to strip.

 

My supermiata radiator came with an o-ring. Not ideal but it doesn't leak.

 

I contacted Supermiata and received a lightning quick response. They recommend using an o-ring.

I like the idea of a bonded washer since an o-ring can squish out.
Looking at using something like this.

 

Those will work, as will this style that is sold at most hardware stores. I used 3/8" washers instead of M10 since it made them extra tight radially around the threads, but any bonded sealing washer for a bolt should be tight enough to seal to the threads in addition to a face seal.

 

+1 to dowty seal/bonded washer. Bought mine from mcmaster but don't have the part number anymore. I never felt good about that o-ring.

 

I had problems with mine as well. Threads were stripped and the gasket/o ring didn't seal right.

Ended up welding -4an Male bungs on the drains and using -4an caps.

 

almost smoked my engine today. full coolant a week ago, none today. found out when things smelled "hot". replace those washers y'all.