Plastic Block Drain Plugs

[TyeeMan]

Hey Everybody,

I've got the nice blue plastic drain plugs on my 5.7L Mercruiser. Got to installing them this weekend and firing up the engine, and it looks like a have a leaking/cracked plug.

I saw a post a while back (did a search and couldn't find it) on this same subject and I thought someone posted a picture of a replacement drain plug that was either stainless steel or brass.

Was I seeing things or is there actually a metal replacement plug for the blue plastic plugs? If so, where can I purchase about 6 of em?

Thanks in advance.

 

[Scott Danforth]

Hardin marine has the stainless ones. https://www.hardin-marine.com/p-810...mercruiser-22-806608a02-8m2000874-5-pack.aspx

I think CP performance as well. https://www.cpperformance.com/p-810...mercruiser-22-806608a02-8m2000874-5-pack.aspx

Michigan motors also stocks the Hardin plugs https://www.michiganmotorz.com/stai...jb7xZt70zkaaztGLSpu6Hn5PjwR0aPEoaAhyPEALw_wcB

in a pinch, a stainless 1/2"-13 bolt, 3/4" long with two flat washers and an o-ring will work too (its hard to find a 1/2" bolt only 1/2" long)

 

[TyeeMan]

Awesome, thanks Scott!! Looks like Michiganmotorz will be my choice as the other two sell packs of 5 and I need 6. Michiganmotorz sells them singly.

 

[wingless]

Those blue plastic Mercruiser parts have been working great for me for years.

They are installed and removed during every usage so I can flush / drain / dry my exhaust.

 

[TyeeMan]

Visually mine look like brand new, no cracks or anything. It's just the one plug started leaking what seemed like through the pores of the plastic.

I'm sold on the stainless plugs tho, , they look nice too. :joyous:

 

[H20Rat]

The blue plastic ones are cheap... I get a couple seasons, and then they get tossed overboard (in the trash, not water...) and replaced with a new set, which usually cost about $3.00.

 

[Scott Danforth]

Visually mine look like brand new, no cracks or anything. It's just the one plug started leaking what seemed like through the pores of the plastic.

I'm sold on the stainless plugs tho, , they look nice too. :joyous:

Plastic has no place anywhere on an internal combustion motor - the operating temperature of the motor is many times higher than the operating limits of the plastic material, too bad the accountants dont agree.

 

[Solito]

Run far from these plastic drain plugs! I just installed a new Mercruiser (383 Mag Stroker) last March. During a recent trip offshore, I noticed my bilge pumps were turning on excessively. Sure enough, I discovered that the top portion of the plug going into the Gen III cool fuel unit severed off for no apparent reason whatsoever and water was shooting through the hallowed portion of the piece broken off in the unit into the engine compartment. When I tried to remove the broken piece still in the unit after the trip, it kept disintegrating on me to a point I ended up damaging the threads. I was able to screw in a spare plastic plug that came with the motor as a temporary fix, but not easily (I still need to clean up the threads with a tap).

Some of you may have not of had any issues with these. But there is NO reason why one of these should have failed on me! I really think making these out of plastic was really lame.

 

[Deepwtr]

If you have a manifold get slightly hot, they will turn very brittle if they don’t outright break. So at least they don’t ruin your day right then, they will ruin your day the next time when they crumble.

 

[Solito]

Here's a picture of what I was referring to in my post above.

The screw below is what I used to plug the hole until I got back to the slip.

I just ordered a 5 pack of Hardin Marine stainless steel replacement drain plugs to replace the plastic junk OEMs. One would think that if somebody was willing to invest $10K-$12 in a new motor, Mercury Marine would be mindful to use quality drain plugs. Unbelievable...

Sorry for hijacking the thread. The timing was perfect given that this happened to me just 4 days ago.

 

[Solito]

If you have a manifold get slightly hot, they will turn very brittle if they don’t outright break. So at least they don’t ruin your day right then, they will ruin your day the next time when they crumble.

The engine compartment on these Shamrock boats are pretty cramped, which limits ventilation. Therefore it gets pretty warm in there. I theorize that this is what caused the drain plug to become brittle and prematurely fail on me.

 

[Scott Danforth]

Solito , you realized you hijacked a thread, correct? its also at the raged edge of the 90 day mark

you also realize that none of your photos will show up because you dont have enough posts yet to be able to post in open forums (it was in the rules you read)

 

[wingless]

...you also realize that none of your photos will show up because you dont have enough posts yet to be able to post in open forums (it was in the rules you read)

It is not in the rules but it is in the linked photo tutorial.

 

[wingless]

Plastic has no place anywhere on an internal combustion motor - the operating temperature of the motor is many times higher than the operating limits of the plastic material, too bad the accountants dont agree.

There is plastic all over the place on every consumer grade engine.

Yes, the material selection should be appropriate for the application. The material should have an appropriate lifetime and should tolerate extreme conditions, but I don't require military components on my boats.

 

[wingless]

Hardin marine has the stainless ones. https://www.hardin-marine.com/p-810...mercruiser-22-806608a02-8m2000874-5-pack.aspx

Those look very nice, but for my application I will retain usage of the blue plastic plugs.

My usage is to remove / replace the blue plugs after every usage, while the engine is at operating temperature, for draining salt water, then fresh water flush, soapy water flush, Salt Away flush, then drain bone dry until next usage.

My blue plugs still look brand new after three years of usage.

It would be less useful for me to grab onto potentially hot metal parts for my flushing, instead of these plastic parts.

 

[scoflaw]

My usage is to remove / replace the blue plugs after every usage, while the engine is at operating temperature, for draining salt water, then fresh water flush, soapy water flush, Salt Away flush, then drain bone dry until next usage

You must not use your boat much. Could not imagine doing that daily. You must slip that 380, how's that work ?

 

[Scott Danforth]

There is plastic all over the place on every consumer grade engine

Not arguing that, its done for profit reasons. however any plastic component is the first point of failure on any engine. Plastic doesnt age well when subjected to repeated thermal cycling

pick the intake manifolds or fuel lines that GM did - high probability of failure under 100k
look at the intake manifolds that Ford did. there was even a recall
look at plastic carburetors that Briggs did, the heat from the engine warped them
look at all the plastic components that fail on any engine.

Yes, the material selection should be appropriate for the application. The material should have an appropriate lifetime and should tolerate extreme conditions, but I don't require military components on my boats.

agreed, however the average lifetime of a plastic part in a marine engine bay is about 11 years. it is shorter if subjected to UV. the plastic drain plugs are recommended to be replaced every year.

its not about military components, its about a material that will not fail and leave you stranded

for decades prior to the troublesome plastic plugs and the overly complex cooling drain systems designed by the hypercomplexification folks at Mercruiser, there was simply a brass plug in each the side of the block, and 1 or 2 in each manifold

plastic thru-hull fittings failing is one of the leading cause of moored boats sinking

 

[Lou C]

I'm in agreement with the idea that plastic drain plugs in this application are not such a great idea, they 'solve' a problem that did not exist in the first place...if you use proper maintenance practices...
OMC and Volvo used brass plugs...that do not corrode...last forever...and all you have to do...is put a bit of Evinrude gasket sealer/Merc Perfect seal on the threads...and they will not leak...nor will they get seized in the engine...even on raw water cooled blocks and exhaust manifolds...so WHY go to a plastic plug that can break...off in the engine...in an nearly inaccessible place...

I've had the same metal plugs in my engine for all these years...they come out once a year...for winterizing...and go back in with just a bit of gasket sealing compound....and never caused a problem...I have a small adjustable wrench that fits them perfectly....If I had a Merc I/O the first thing I'd do...is remove and throw out those plastic plugs and replace em with metal...just don't forget the gasket sealer...

 

[wingless]

My usage is to remove / replace the blue plugs after every usage, while the engine is at operating temperature, for draining salt water, then fresh water flush, soapy water flush, Salt Away flush, then drain bone dry until next usage

You must not use your boat much. Could not imagine doing that daily. You must slip that 380, how's that work?

The boat is currently used on the weekends.

My custom designed flush / drain setup is okay to perform.

Prior to my exhaust redesign from impossible to drain, impossible to flush, always retaining salt water 24/7/365, I was getting three to four years from the OEM Mercruiser parts before having to discard those obscenely expensive cast iron parts. I just performed my three year disassembly / internal inspection and my parts still look to be in brand new condition.

My guess is that my salt water parts will now last the life of the boat.

Yes, my boat has always been docked in salt water.

 

[wingless]

the plastic drain plugs are recommended to be replaced every year.

Please provide the link showing that recommendation.

FWIW, on my boat if these parts were to fail while stationary / docked, that failure would not cause water intrusion.

If these were to fail while underway, then I would get alerts at the helm and my three bilge pumps would have zero issue remaining ahead of the raw water pumped water ingress.

There are several of these that are original to the boat. They pass visual inspection when removed for periodic safety inspection.

plastic thru-hull fittings failing is one of the leading cause of moored boats sinking

The Forespar Marelon seacocks are UL rated and meet ABYC standards for below waterline usage.

Are these parts unacceptable for below waterine usage?