Why did my plastic drain plug break off?

[Tmakaro]

I have a 2010 bayliner with a 4.3l mercruiser. A couple weeks ago while I cruising along at about 3400 rpm, my boat overheated. It turns out the engine block has a blue plastic wing nut drain plug and the top broke off draining my engine block. I fixed it and fast forward to yesterday it happened again to the other side. This time, after trolling for a few hours, I gunned it to 4000 rpm for maybe a minute before it overheated.

what would cause this to happen? It’s been fine for 10 years. Just brittle?

 

[alldodge]

They break over time because there plastic, and also because they are tightened to tight. Plastic plugs should be replaced every few years. Can also get stainless steel ones from Hardin marine

https://www.hardin-marine.com/p-810...-plugs-mercruiser-22-806608a02-8m2000874.aspx

 

[Rick Stephens]

They turn to dust. Replace them every few years or get the steel ones.

 

[Tmakaro]

Thanks everyone. I wouldn't mind so much if I broke them off at home but in the middle of the ocean! :grumpy:

 

[Lou C]

Those like the single point drain with plastic housing are some of Merc’s less good ideas!
Replace with metal and just put a bit of gasket sealer on the threads they will come out easy. I have the same brass ones my engine came with and it’s 32 years and old! And in salt water as well!
coat threads with Merc Perfect Seal or Permatex Aviation Sealer.

 

[Grub54891]

Had a guy come in with the same issue. He was a bit upset as he had to use the kicker motor to get home. We sold him new plugs but he didn't want the metal ones. So I suggested to keep a dry stick onboard so if it happens again, put the stick in the hole to get ya home. It's the little things that can get ya.

 

[Scott Danforth]

what would cause this to happen?

Plastic has no use being used in a cooling system or on a motor

remember, the plastic plugs cost Mercruiser under $0.03 each. that is why they use them