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Old 09-04-2021, 12:25   #1
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Blockage in raw water circut

We had our water pump">raw water pump fail a few months ago, and had salt water intrusion in our oil. After many oil changes and rebuilding the pump, we've realized the issue was really a clogged system.

Today we've found the blockage. It's after the heat exchange and the anti-siphon, just in the hole that goes back into the engine, where it mixes with exhaust, then goes out the elbo, lifting muffler, etc. Looks like a calcium buildup.

You can see the blockage here: https://imgur.com/a/t5pCFAI

What should our next step be?

This is on a Volvo Penta MD21B
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Old 09-04-2021, 18:27   #2
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Re: Blockage in raw water circut

I may be confused about this but on our old Volvo (may it rest in peace) the water intake on the mixing elbow would clog about every 18 months. After a while I always carried a spare and would take the clogged elbow to a radiator shop to be boiled out.
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Old 09-04-2021, 18:30   #3
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Re: Blockage in raw water circut

you could use caustic soda then flush it once a year as many do !
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Old 09-04-2021, 18:43   #4
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Re: Blockage in raw water circut

Quote:
Originally Posted by madworld View Post
We had our raw water pump fail a few months ago, and had salt water intrusion in our oil. After many oil changes and rebuilding the pump, we've realized the issue was really a clogged system.

Today we've found the blockage. It's after the heat exchange and the anti-siphon, just in the hole that goes back into the engine, where it mixes with exhaust, then goes out the elbo, lifting muffler, etc. Looks like a calcium buildup.

You can see the blockage here: https://imgur.com/a/t5pCFAI

What should our next step be?

This is on a Volvo Penta MD21B
Remove the item and clean it out by using (initially) a mild acid and progress to a stronger acid it required. CLR is a good mild acid mix but if that doesn't remove it, go straight to HCl (hydrochloric / muriatic acid) but do take sensible precautions when using it as it is strong enough to be nasty.

OR

Replace it with a new part.
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Old 09-04-2021, 18:43   #5
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Re: Blockage in raw water circut

Clearing a clogged exhaust elbow is routine maintenance item on most marine engines and generators. With some designs of elbows, engines, and water systems it can be very frequent, as much as every few hundred of hours of operation or as much as a few thousand hours.

Depending on your personal attachment to time or cash, you can replace or try to clean. Many of the OEM elbows are black iron, or in the worst case plain steel, and are usually about ready to die from corrosion when they clog, so cleaning can be an exercise in futility.
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Old 10-04-2021, 09:05   #6
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Re: Blockage in raw water circut

No use to try and repair. Just tear it out and replace it. Its not only blocked but also corroded.
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Old 10-04-2021, 10:20   #7
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Re: Blockage in raw water circut

My experience with mixing elbows does not match the previous two posts.After removing the iron mixing elbow and having it boiled out at a radiator shop I did get reasonable use from it. No doubt some elbows are better than others.My current engine a beta 38 is 8 years old and 3000 hours with original elbow and no maintenance.
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Old 10-04-2021, 17:47   #8
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Re: Blockage in raw water circut

For what its worth, I have had great success with cleaning exhaust elbows using the electrolytic rust-removal technique. Simplified, you take a bucket of water with baking soda (an electrolyte), a 12v battery charger, a hunk of scrap steel (rebar is excellent) and some leads. Hook them up overnight and eureka, a nice clean bit of work. Google it to get the polarity correct.

A trick: take a piece of PVC, drill lots of holes in it and put the rebar inside. Place the assemble inside the exhaust elbow (the PVC is an insulator, the holes let it all work).

An advantage over acid baths: it will NOT damage the base metal, heck, it wont even damage the paint.
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Old 13-04-2021, 14:13   #9
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Re: Blockage in raw water circut

[QUOTE=My current engine a beta 38 is 8 years old and 3000 hours with original elbow and no maintenance.[/QUOTE]

Your Beta stainless steel exhaust elbow was designed to last the life of the engine and not require maintenance.
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Old 13-04-2021, 19:32   #10
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Re: Blockage in raw water circut

Thanks FPNC
Based on my experience with my current elbow I agree that it lasts. I do carry a spare since I replaced a Volvo when I changed to Beta and I was used to changing and cleaning elbows. Who knew that some elbows were long lived? Certainly not me.
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Old 13-04-2021, 21:19   #11
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Re: Blockage in raw water circut

If you want a non toxic, PH neutral solution, I use Archoil AR5100. 8oz makes 1 gallon solution. It removes corrosion from metals without harming the base metal. It's concentrated and mixes 1:15 with water. Something like a clogged exhaust riser will be rust free in an overnight soaking (depending on temperature). Use hot water, be done in minutes. And when you're done, you can dump it down a drain or pour it over the side. Available at archoil.com and sometimes on Amazon and ebay.
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Old 15-04-2021, 07:55   #12
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Re: Blockage in raw water circut

Careful with caustic soda (lye) -- it can eat an at first painless hole in your flesh. A splashed drop in your eye can cause corneal scaring.

The boiling tank at a pro radiator shop is the way to go. BTW, caustic soda will not damage the metal like acid.
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Old 15-04-2021, 16:38   #13
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Re: Blockage in raw water circut

Our previous boat's engine was raw water cooled. Jim would circulate a HCL (swimming pool acid) solution through the cooling passages once a year. On ours, one of the worst points was a sharpish corner in the head. You can hear it stop bubbling when it has finished reacting with the salt buildup.

I think Lepke's solution mentioned above might even be better, if you can source the product.

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Old 19-04-2021, 04:31   #14
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Re: Blockage in raw water circut

I believe it to be a good product https://www.archoil.com/collections/...0-rust-remover
but not available since 5 years in Europe
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