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Old 14-01-2015, 17:40   #1
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Volvo MD 7/A Waterflow

Greetings - This is my first post, though I read this forum quite a bit. I know this issue has been addressed elsewhere here, but I haven't quite found what I seek, I guess.

I have a 1980 Sabre 28 w/which I bump around MidCoast Maine. It has a raw water cooled Volvo Md 7/A . I bought it 4 years ago and it has been relatively hassle-free. I love it. Anyway, the waterflow out the exhaust isn't what it should be. Additionally, the Temp Gauge will jump up if I run it full throttle too long, but quickly settles to normal when I ease it back. From a usage standpoint, this really hasn't been much of a problem, I just don't run full, or close to full throttle often and I've managed. My buddy is a marine Engineer and he says it could run that way for the next 10 years w/out issue provided I keep an eye on it.

Anyway - I Winter and Service the boat at a nearby Shipyard that I like thus far. They have told me that these engines essentially rot (rust) from the inside out and outright engine failure is inevitable, but measures can be taken to prolong it's life. I guess I agree, I'm not mechanical but am sloooowly learning a bit via this engine. Below is an email from the yard, I'd be most appreciative if some of the mechanically inclined folks here could share your thoughts. Thanks much - Chris (I've changed the names to protect the innocent)


On the engine, I met with Joe, our diesel mechanic on the engine. Last year we did the following to help with the cooling situation.
1. We removed the elbow and cleaned it. It was in pretty good shape.

2. We removed the thermostat and its housing. The housing was filled with rust and sediment which we cleaned.

3. We replaced the thermostat.

Joe and I discussed trying a radiator cleaner (ex: Rydlyme) on the engine. He recommends against it. Loose sediment dislodged by the harsh cleaner may cause clogging down the line.
He recommends a thorough flushing it with fresh water and then running non-tox antifreeze through it. This is leaves the engine clean and protected for the winter. Remember that this is an old saltwater cooled engine. Itís life-expectancy is limited. There is nothing we can do to reverse that, but the right measures might slow down its internal deterioration.
On the exhaust manifold, if we can free up the bolds to remove it, it might benefit from an acid bath. BUT, as with any rusted bolt, you run the risk of snapping it off. If one were to break in the wrong place, we might have to remove the engine to repair it. Iíll have Joe look at it and see what he thinks.
Guess thatís it. Mike

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Old 14-01-2015, 18:28   #2
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Re: Volvo MD 7/A Waterflow

I'm another MD-7A piker. I have one in the boat and one in the basement.

I don't see anything wrong with their email.

Being basically lazy I would try running it with the new thermostat to see if changing the stat helped at all.

The cooling systems are a bit of a cludge. The pump, exhaust manifold, and stat has these weird slip in fittings.

When I got my boat the engine had just been rebuilt, which was fine, but they skimped putting some things back together. It took me a very long time to get all the kinks out. For a long time the engine would overheat every once In a while. Drove me nuts.

So it turned out the problem was they used silicon on the transmission fitting instead of a compressible copper washer, and once in a while it would suck air. The temp would shoot right up.

Once I got that the engine has been good, although it is now running cool. Go figure.

I have had the exhaust manifold off on both engines, no problem. If you DO take it off, replace the fuel line banjo fitting while you are there. Or at least modify it so that you can disconnect and replace the hose should you need to. Otherwise you need to remove the manifold to change the hose.

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Old 14-01-2015, 19:04   #3
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Re: Volvo MD 7/A Waterflow

Volvo Penta Schematic Part Diagrams

Exploded parts view. / Len
My personal experience & humble opinions-feel free to ignore both
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Old 15-01-2015, 09:17   #4
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Re: Volvo MD 7/A Waterflow

I have to agree with the yard about removing the manifold. I pulled the manifold from my spare parts engine, and broke 2 bolts off. It wont be a difficult fix on the shop bench, but would be very difficult in the boat. Just my 2 cents worth. _________Grant.
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Old 15-01-2015, 20:18   #5
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Re: Volvo MD 7/A Waterflow

If the engine has an MS or MSB transmission, check that the transmission cooling water jacket is clear.

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Old 18-01-2015, 15:00   #6
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Re: Volvo MD 7/A Waterflow

Hi Chris,

I have a 1980 Sabre 28 with Volvo MD-7A as well, bought it this summer. The Volvo has kept things interesting and quite the learning experience. The injector pump died while bringing the boat home. In the process of replacing that injector pump I also rebuilt the water pump as it was showing a lot of wear and had a bad seal causing leakage.

By the end of the season I was measuring hot spots on the exhaust manifold and head. From reading a bunch of material this is apparently a common problem. What happens is salt and other gunk build up in the water channels and that reduces flow and causes overheating. Removing the exhaust manifold and cleaning out the passageways is apparently the best course of action for this.

In this thread

Volvo MD7A Overheating Solved? - SailNet Community

You can see some pictures of what this looks like.

Cleaning out the water pump hard lines and the passage through the transmission is a good idea as well.

I am going to be pulling the exhaust manifold and cleaning it and the head out as much as I can. I'm then planning on putting it back together and flushing a bunch of citric acid through the system to try and clean it out further. After that I am planning on converting to fresh water cooling to try and avoid this in the future and to hopefully prolong the life of the Volvo.


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