MD7A Exhaust/Water Manifold (I am so sorry)

[Ramona]

I have an MD7b in my Currawong 30 and it is an excellent engine. It does suffer from a build up of calcium from time to time but is an easy fix. Normally will require descaling every 12 to 18 months or so.
What I do is disconnect the hose from the water pump and add a couple of feet of hose with a temporary joiner and fix it above the height of the engine. Disconnect the other end hose that goes to the exhaust elbow and secure that to the same height as the other hose. Blow out any water left in the system. Add a phosphoric acid mix, I use a local product called "Metal Gleam" 5:1 with water. Only need a liter or two of mixture and pour that into the system and let it sit for an hour or so. This acid does no harm to any thing in the engine except calcium. You can use barnacle buster if you like but it's the same stuff at 10 times the price. Don't bother with CLR or vinegar, takes too long. I did comparisons with seashells in jars and there is no comparison. Do watch a few Barnacle Buster Youtube videos though.
After a couple of cups of coffee just flush the foaming crap out, reconnect the hoses and run the engine.

[MicHughV]

yep, my preference would be to junk that engine and get a new one....a fresh water cooled one... That engine must be at least 40 years old, and those clogged cooling passages were a pain in the butt.
Mine ran for around 10 years in salt water (1980-1990) Amazingly robust, despite the odd salt water bath her and there, it never stopped running, but maintenance was a chore, plus Volvo parts typically cost an arm and leg...and despite that monster flywheel, it was not a very smooth running diesel, especially so at idle, when it had a tendency to dance a jig.

And I seem to recall, it was quite a heavy engine. 400 lbs plus.

Equally amazingly, when I pulled my MD7 to replace it, I found a buyer for it. Apparently, there are a lot of those old Volvo engines around, whether people use them for parts or just try to rebuild them I don't know.

It would possibly be ideal for a fresh water boat?

[MicHughV]

I was able to find a service manual for that engine online...
just google "Volvo MD7 service manual" and you'll find it.
Lots of other Volvo MD7 stuff online as well.

[Wotname]

Originally Posted by davenrino

The cooling system is why I replaced my MD7a besides parts availability and price. Salt water pumping through a hot cast block...what could go wrong? .............

Not much actually! It is a very straightforward simple cooling system and remarkably robust. Obviously the engine must be designed for raw water cooling and not just an industrial design adapted to use direct sea water.

And it must be maintained properly - the anodes have to be replaced before they are eaten away.

Yes, scale (calcium carbonate) will build up especially if the engine is allowed to run hot. The scale should be removed periodically by flushing with acid etc - IMO very 500 hours or less.

Yes, there are many raw water cooled engines replaced because they have rotted out but likewise there are also many that are still in service after 40 years of service and are still in good condition internally. It is all due to proper maintenance or the lack thereof.

Of course, coolant cooled is better, requires less maintenance and it does allow an engine to be operated at a higher temperature which is a good thing.

[davenrino]

I had only had the boat a few months when water started leaking from the manifold where the copper pipe attached and from the thermostat housing. I found new seals and a used copper pipe in better condition than mine on ebay but there wasn't enough metal left on the manifold for it to seal. I found a new manifold for over $3000 plus shipping from Europe to Hawaii, but the thermostat was "Obsolete" and I couldn't find one anywhere. I gave up the fight.

[Wotname]

Originally Posted by davenrino

I had only had the boat a few months when water started leaking from the manifold where the copper pipe attached and from the thermostat housing. I found new seals and a used copper pipe in better condition than mine on ebay but there wasn't enough metal left on the manifold for it to seal. I found a new manifold for over $3000 plus shipping from Europe to Hawaii, but the thermostat was "Obsolete" and I couldn't find one anywhere. I gave up the fight.

I get it, I would toss in the towel also. You can't overcome past maintenance sins!

I might have made up a new manifold but then again I have the time, the interest and most of the facilities to do so. I understand that many haven't.

I will be probably be making a new manifold to replace the one I pictured above but it doesn't matter if it takes a week or more of work (and a hundred dollars).

A new replacement engine has a lot pluses .

[MicHughV]

After my love/hate affair with the MD7, I replaced it with a Volvo 2003 series engine...3 cylinder with a bit more hp...27 I think.

But both engines were a pain in the butt. For reasons beyond my understanding, Volvo uses these weird rubber compression inserts at the end of their cooling water pipe fittings, which were a never ending source of grief for me. I did attempt several " modifications" to this system, which resulted in an improvement, but still not perfect.

My MD7 had the 7 degree downward sloping gearbox, which suited my particular installation and was the reason I replaced it with the 2003 Volvo engine, which had a similar 7 degree downward sloping gearbox.

Were it not for that, I would not have replaced one Volvo with another. My 2003 Volvo also had intermittent gearbox issues, where it would not go into gear properly. Volvo has this strange cone clutch system, which was the root of the problem. I had my gearbox taken apart by an expert mechanic and he replaced this cone, but I could not visually tell the difference between the new and old one, so the tolerances must have been minute.

I have read countless threads about people's dislike of Volvo engines...price...maintenance issues, etc..

I don't dispute that they are robust engines, but it's the little things that were very annoying.

Initially, I would get my oil filters directly from the Volvo dealer at a whopping price. I later found several other oil filters from NAPA, an auto parts dealer for about 1/4 the price.