MD7A raw water maintenance question - Barnacle Buster

[JD-MDR]

"I never got a definite answer. What I concluded was that it must be a built in anode of zinc or some other material. After cleaning out the exhaust and water channels in the manifold, I couldn't find where that plugged up port would connect to any channel inside the manifold. There was definitely a softer metal material beneath the layer of crud inside that port. I left it as is and put it back in operation. Engine is running fine". (I just pasted that in from a cruiser forum). I may just pull the manifold off again to work on that leaky pipe. Now that I got the hang of it. Its pretty easy. It seems like none of the mechanics are familiar with that old engine. They all need to look at the manual. But we can do that ourselves. If I remember right when I was running the hose thru it the little ports were connected to the big round port. I'm going out on another CD this weekend. Hopefully I'll get time to work on it next week. I starting to worry that maybe I shouldn't have chipped out that round port. I just found something interesting, google " MD7A exhaust manifold mystery hole". I can't attach the link.

[mgphl52]

It seems like none of the mechanics are familiar with that old engine.

Could this be because they were still in diapers when our MD7's were built???

[JD-MDR]

I got ahold of Karl at CC Marine in MarinaDelRey. He’s always so helpful when you can catch him. He is an authorized Volvo shop. His manual l shows the port open. He can’t figure why it would be closed. He said run the piss out of it and check the temp. Good News. I hope I’m OK

[S/V Ethan Grey]

Since you're looking at all the potential sources of engine overheat issues, take a look at your exhaust hose and make sure it's not delaminating. Mine is and I'm going to replace it.

exhaust hose.jpg

[JD-MDR]

I replaced all the hoses and thermostat last year. Today I ran the engine for about 45 Minutes in gear at 2000rpm's. I t seems fine but the water temp gauge is at the border between green and red. I think I will get a laser temp and check it better. I think maybe it's a little warm. Maybe not. It is no different than when I first started this project. I sent out some email to
Volvo reps trying to get an official word on the plugged port that I bored out.

[JD-MDR]

I decided to take the manifolf off again. I soaked it again in muriatic solution and cleaned it up much better. I wanted to confirm that the mystery hole was not connected to anything but the water So its OK. Im no expert but im pretty sure that was plugged with carbon. It looked so nicely plugged like ke it was done intentially. Any wayI bent the coolant pipe a little so it has some upward force on the manifold. I think I stopped that leak. I measured the temp at the freeze plug on the cylinder head 142 degrees. It was 156 at the freeze plug on the manifold. This thread has been a big help. Thanks everyone. Oh one tip. When working on the manifold. Take the temp sending unit off so you dont break that little tab off $120. I knew that was gonna happen

[Kickin Bears]

Awesome job JD! Been great following your work.

For those of us that have the volvo penta md7a, the lifespan is almost entirely based off of the water manifold. Primary reason I’m taking preventative steps in preserving it. I think the engine is bulletproof otherwise; mine has been super reliable/consistent. A mechanic at hartge was able to start one up that had been under water for 16 months, which is amazing

I’m seriously contemplating replicating your work to be thorough. I agree re: the manifold hole. The gasket wouldn’t have a hole there if water wasn’t supposed to flow between manifold sections. Crazy that it can clog like that, and there are multiple cases of this happening so something to be aware of

[JD-MDR]

my parts arrived today . I ordered from Keypart.com . I think they are in England. . I got the decarb gasket set and the water temp sender and waterpump rebuild kit and 4 oil filters. . It came fast 3-5 days and the quote was pretty good $235. But $305 got deducted from my account. I guess the gov't had to take a cut. So I don't know how good a deal it was. I think It might have been about 410 from the local Volvo dealer includes tax.