2004 Mainship 400 Fresh water flush cap Q.

Has anyone installed a fresh water flush cap on top of or inline with the raw water filter on a 2004 Mainship 400? I will be taking a picture of my filter later today and will post it here. Hopefully, the brain trust will confirm which one to order online. I read the other threads on this topic which I believe were for a MS 390. Started this thread because my setup is a single Caterpillar 3126B.

Here are the pics.

View attachment 136996

Grocco makes an engine flush kit. I've used this on A/C sea strainers for both winterization and priming.

https://defender.com/en_us/groco-ssc-series-engine-flush-kit

What is the diameter of the opening on top? I used to use a SeaFlush to winterize our last boat. It can also be used to flush the engines with freshwater.

Tom, I bought this flush cap for the A/C strainer and the threads didn't match so it didn't fit the Marine Hardware strainer. I can't get the SeaFlush to fit in the strainer because it's too close to the bulkhead, but if you are trying to flush the main engine strainer the SeaFlush works pretty well. For the A/C strainer I bought a "duct plug" which someone on YouTube was using. As you tighten it up the rubber plug expands and seals the opening. You might be able to find one that fits the main strainer, mine is meant for the A/C strainer for my next winterization. Before you buy the flush cap you might want to try and see if the threads are the same. The 1-1/2" one I bought only went in a thread or two and didn't work for me.

Another approach might be to add a pipe T to either the inlet or discharge side if the strainer. And use the "extra" port as the connection point for flushing.
I did exactly this on my A/C strainer for winterizing. The A/C pump won't self prime so I winterize my raw water wash down system first and use a short hose to connect to my A/C strainer with pick up closed and feed pink throughout the A/C system. Also helps in spring if A/C system won't prime.
If done frequently you could plumb dockside water to the strainer w a valve to activate.

I just took my existing caps and drilled and tapped in 3/4NPT threads, then silver soldered in bronze nipples.

lwarden said:

I just took my existing caps and drilled and tapped in 3/4NPT threads, then silver soldered in bronze nipples.

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another problem. The cap to my 200 Marine Hardware raw water strainer is stuck. Tried unscrewing by straddling and turning the tabs on the cap with a thick/xl screw driver layed sideways. Wouldn’t budge even after lubricating with WD-40 like silicone spray. Will try channel locks tomorrow. Please reply if any other advice.

Bay Retriever said:

another problem. The cap to my 200 Marine Hardware raw water strainer is stuck. Tried unscrewing by straddling and turning the tabs on the cap with a thick/xl screw driver layed sideways. Wouldn’t budge even after lubricating with WD-40 like silicone spray. Will try channel locks tomorrow. Please reply if any other advice.

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You will get better responses with your own new thread along with a photo or two of the strainer in question.

Bay Retriever said:

another problem. The cap to my 200 Marine Hardware raw water strainer is stuck. Tried unscrewing by straddling and turning the tabs on the cap with a thick/xl screw driver layed sideways. Wouldn’t budge even after lubricating with WD-40 like silicone spray. Will try channel locks tomorrow. Please reply if any other advice.

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Maybe a long pipe wrench. Luckily mine come off relatively easily. The Marine Hardware strainer lids have the two ears that stick up which look like they might break if torqued too hard. It also has a square drive that looks like it would accept either a square insert or a monkey wrench/pipe wrench. I would try to work it loose using the square drive rather than the ears.

It's bit tricky to get a purchase on the drive because the ears are in the way. Maybe you can find a socket that fits inside the square and use a breaker bar or something like this.

You might be able to use a chain jaw stuffing box adjuster spanner(aka chain wrench) to grip around the screw top fitting. Bought mine on ebay.

Any square bar across the ears should work. I have used a large open end or adjustable wrench. Tapping with a hammer / mallet may help.
I'd replace the original and apply some water resistant grease before reassembling. It doesn't take much torque to seal a good oring.

Bay Retriever said:

another problem. The cap to my 200 Marine Hardware raw water strainer is stuck. Tried unscrewing by straddling and turning the tabs on the cap with a thick/xl screw driver layed sideways. Wouldn’t budge even after lubricating with WD-40 like silicone spray. Will try channel locks tomorrow. Please reply if any other advice.

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Mine frequently gets stuck, maybe I over tighten them? Anyway, when I can’t break them loose with leverage, I tap them with a hammer. Works every time.

Dougcole said:

Mine frequently gets stuck, maybe I over tighten them? Anyway, when I can’t break them loose with leverage, I tap them with a hammer. Works every time.

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You don’t have to hit them hard, something about the shock pops them loose, like tapping a jar lid with a butter knife handle.

Ended up having to replace the sea strainer. Purchased a Grocco ARG 2000S. Also purchased the fresh water flush cap so I can periodically run fresh water through the Heat Exchanger and barnacle buster too.

+1 on the waterproof grease. I'm an over-tightener by nature, but am much better about not going nuts on the strainer lids (just a bit more than hand-tight). That and the grease has been a big help. I did break the ears off the one of the lids using a very big and long screw driver to loosen a stuck one, but in general that works well. The sea-flush works fine on all my strainers including AC on my 2005 40T. It must be mounted a little further from the bulkhead compared to the earlier mentions about it not fitting. I was never successful using a socket/driver on the square 'hole' in the lid - it wasn't an exact fit and deformed.

Yes, carry a can of silicone grease and keep them lubed and then don’t tighten them to Godzilla torque.