TOPIC:

If you have a Mercruiser and do any of the winterizing work on it yourself, you'll likely recognize these little blue drain plugs which screw into the engine block and manifold to drain the raw water out of the motor. Not only are they tough to access in my boat but they are easy to cross thread when replacing.

Once, while fishing waynell offshore, one of them broke. Unluckily, they have a hole in them so while the motor was running it was pumping water into the bilge. Luckily, since they have a hole in them, it was fairly easy to fit an easy-out in the plug and remove the broken off "stump" still in the engine.

Since the plugs are plastic, once cross threaded they are worthless. I always keep a couple of spares close at hand. When buying a new supply a couple years ago I came across these stainless steel after-market plugs. made by Hardin Marine.

The Good News: I've not had any issues with these since I bought them.
The Bad News: They are currently back ordered and probably not available the rest of the year.

So Stock up on the blue plugs and cross your fingers you don't cross their threads of break them off.

Good tip Mike. Those are -AN straight thread fittings and metal versions can be had from local hydraulic shops or Summit Racing in anodized aluminum.

Another tip is to use some grease on the o-ring when installing after draining for the winterization. This will make them seal with less torque and in-screw a lot easier.

I'm not saying that's wrong - I'd never heard of threads called AN previously - though I've probably used them dozens of times. Who knew? The AN stands for Army-Navy. Thanks internet! It certainly makes sense for Mercruiser to use a readily available thread, but it makes almost as much sense (or nonsense) for them to invent a proprietary thread so folks would have to buy those little blue plugs from them. That being said, the blue plugs appear to have a thread "more coarse" than other bolt, pipe and hydraulic fittings I've used.

On older Mercruiser powered sterndrives I've owned the block and manifold drains were threaded with NPT brass plugs. That was terrific since I was able to replace them with radiator petcocks (drains). Once those were in place, I could simply turn the end on the petcocks to drain the motor after early season trips before the danger of freeze was past.

I'll have to see if I can find an adaptor that goes from AN to NPT. That would be a better solution than the metal plugs.

One thing, I wouldn't suggest using an aluminum plug in an iron-block motor. Electrolysis issues.

Mike is correct that Aluminum is sacrificial to steel or Iron in an electrolysis situation. That being said in fresh water it takes many years for the corrosion to take place. Many aftermarket aluminum (and some stock) are available for Mercury motors including cylinder heads, intake manifolds and exhaust manifolds. If used in salt water you better flush with fresh water after each use because the electrolysis is much more prevalent. Hard coat anodizing does a very good job protecting aluminum against electrolysis corrosion when dissimilar metals are used.