MD7A raw water maintenance question - Barnacle Buster

[Kickin Bears]

I’m contemplating running Barnacle Buster through the MD7A raw water cooling system as part of winterization this fall and wanted to get some feedback as to if I should do this or not. I’m reading a number of threads advising against this due to small particulate breaking free and flowing farther downstream into finer spaces, causing greater issues

Anyone have advise on this?

I’m just trying to take action to slow down / delay the corrosion process. The engine seems to run well, does what I ask and just purrs along.

[Capt Rich]

While i’m A fan of Barnacle Buster to keep the cooling system scale free, make sure to rinse really good before adding the pink stuff anti-freeze.

[Kickin Bears]

^^^ thx CR

I see a decent number of views but no other opinion. I’ve heard great things about BB, so think I’ll give it a go.

To help prolong the life of the water manifold / engine, think I will add to my raw water maintenance / winterization list:

- Remove, inspect, and replace (if needed) thermostat

- Run Barnacle Buster through raw water system for a few hours, flush well with fresh water

- Install an inline Perko Flush Pro Tvalve for easy freshwater hookup, and flush the raw water system for ~10m as part of process of closing up boat after arrival at dock

[Keith]

I would;t worry about particles breaking free from barnacle buster. There are so many chunks of rust in there that anything from the barnacle buster would be insignificant.

My MD7A just celebrated it's 40th year of running raw water through the block. Three years ago the head gasket corroded through and while I had the head off I used a long thin screwdriver to pulverized all of the rust chunks that were down in the water jacket. Then I flooded the jackets with water and sucked out the smaller chunks with the vacuum oil extractor. This was an iterative process that took many hours, 3 or 4 I think. In the end I had a sandwich baggie about 3/4 full of rust chunks.

My MD7A always start right up, runs cool and of course make quite a bit smoke With the 2 bladed prop it makes 5.5 kts at 2400 RPMs and 6.2 kts at 2700 RPMs. A stiff current or wind of course knocks that down a bit. I mainly use it for in out of the short channel and it serves me well for the intended purpose. If I was doing serious causing I wold most likely replace with the Kubota (sound marine). The Swedish engineering is truly incredible. Some day it will die and it's long life will be celebrated!

Keith

[S/V Ethan Grey]

Following. My MD7A has been converted to a cycled water cooling system. After reading reviews on BB, I'm thinking about running some through the heat exchangers. My motor is currently running hot, but I can't figure out why. I already replaced the impellers, checked the thermostat, and checked the temperature sender. Anyway, looks like the reviews are good. Keep us posted on your progress.

[JD-MDR]

I have had a few occasions of overheating. Every time it was a clogged fitting . There is a 1/4" fitting that goes into the mixing elbow. ( I think it's somewhere near the mixing elbow) I'll have to check tomorrow. It took me a while to figure it out. At first I overhauled the water pump ,then replaced the disintegrated thermostat. When flushing with rydlyme I found that fitting. And it has overheated a couple times since and it has always been that same fitting.
The 1/2" hoses connect to a 1/4" fitting.

[S/V Ethan Grey]

I have had a few occasions of overheating. Every time it was a clogged fitting . There is a 1/4" fitting that goes into the mixing elbow. ( I think it's somewhere near the mixing elbow) I'll have to check tomorrow. It took me a while to figure it out. At first I overhauled the water pump ,then replaced the disintegrated thermostat. When flushing with rydlyme I found that fitting. And it has overheated a couple times since and it has always been that same fitting.
The 1/2" hoses connect to a 1/4" fitting.

Good suggestion. I'll pull all the connections and see what I find.

[Kickin Bears]

My MD7A always start right up, runs cool and of course make quite a bit smoke With the 2 bladed prop it makes 5.5 kts at 2400 RPMs and 6.2 kts at 2700 RPMs. A stiff current or wind of course knocks that down a bit. I mainly use it for in out of the short channel and it serves me well for the intended purpose.

I tend to cruise at ~1.9k. Sounds like I could get a little more out of her I thought I read somewhere that max RPM recommended was 2.3k-ish but I’ll have to source that


Appreciate to all for the follow on comments!


Taking the manifold apart and picking out rust chuncks is on my future to-do list, purely as proactive maintenance. The thing has performed very well so far; I think it’s a great engine. Too bad they didn’t build a zinc into the manifold somehow to sacrifice

[Keith]

Just to be clear I never cruise at 2700 RPMs just do it for a minutes or so as a base line to see if she is still performing consistently. My typical cruising is at 2300 to 2400 RPMs. 2700 RPMs is the max that I can get out of her under load. The tach goes to 3000 RPMs which I can easily overshoot with no load (in neutral).

[JD-MDR]

I think my manual said 21 is most efficient and 25 is maximum recommended

[S/V Ethan Grey]

From the MD7A manual:

Max. engine speed: MD7A 43.4 rev/sec (2600 rpm).
In order to obtain maximum engine performance, an
engine speed as high as possible should be chosen
but not, however, greater than 43.4 rev/sec (2600
rpm). Idle 650-780 RPM.

West Marine has Barnacle Buster concentrate on sale at 25% off so I picked up a gallon. I'm going to run it through the seawater side of my cooling system tomorrow. Since my MD7A has recycled water cooling, I won't be circulating it through the manifold. I will cycle it through the heat exchangers though. To do that, I bypassed the water pump and removed all of the zinc anodes in the heat exchangers. I plan on mixing a batch in a 5 gallon bucket and cycling through the system with a bilge pump. I'll let you know how it goes.

[JD-MDR]

Thanks David. I might start running mine a little higher. I am out now on anchor. There is little wind all weekend I will probably motor home tomorrow. I noticed coming across my temp gauge is bouncing up and down. I think that means its time to flush again. That 90 degree elbow to my mixing elbow is a 3/8 “ not 1/4 but still the reduction and the sharp turn cause blockage. It wasnt blocked this time. My manifold looks horrible but Im afraid if I take it off. Something will break. I do have the gaskets. I think Ill wait till I really need to take it off. Is BB something like Rydlime or Muriatic acid. I used acid one time on a part. I made it way too strong and really cleaned it. I might have ruined it

[S/V Ethan Grey]

JD-MDR, I believe Barnacle Buster is phosphoric acid and other stuff. Not sure what the other stuff is. There is some discussion online about whether you can just mix your own cheaper...maybe, maybe not.

Thanks David. I might start running mine a little higher. I am out now on anchor. There is little wind all weekend I will probably motor home tomorrow. I noticed coming across my temp gauge is bouncing up and down. I think that means its time to flush again. That 90 degree elbow to my mixing elbow is a 3/8 “ not 1/4 but still the reduction and the sharp turn cause blockage. It wasnt blocked this time. My manifold looks horrible but Im afraid if I take it off. Something will break. I do have the gaskets. I think Ill wait till I really need to take it off. Is BB something like Rydlime or Muriatic acid. I used acid one time on a part. I made it way too strong and really cleaned it. I might have ruined it

[JD-MDR]

I ran home at 2600 RPM's. The motor sounds good and I made good time 6-6.5 kt. The temp gauge isn't really bouncing . But it creeps up to the red then suddenly drops back down. Now you got me going. I may just take the manifold off and bring it to a radiator shop. I've read there is no zinc. The freeze plugs look bad as does the whole thing. I don't think I would go too far with it like this. I had the alternator rebuilt last week and I think I will take my starter in also. I found a good shop. They only charged me $95 to rebuild the alternator. He said it was good a thing i brought it in. It was really bad. For all I know they may be 50 years old. What I'm worried about is will I be able to rebuild the block when the time comes before I get too much money in this ???

[JD-MDR]

Took the manifold off and soaked it in muriatic acid and water 6-1 ratio for two 10 minute soaks also soaked the thermostat housing and the mixing elbow. It wasn’t as bad as I thought. I’ll put it togeather. t tomorrow. Luckily I had the gaskets. Cant figure out what the round mark. I mean the about 1” round mark between the two square exhast ports The gasket has a hole for a port but the manifold and the head are either completely plugged or they not anything??? I wish I would have ordered a manual.