ah yes, the Volvo
MD7A...my old nemesis...I had the MD7B....same engine but with a downward sloping transmission
....had it for many years on my first boat.
You do know off course, that it is a raw water
cooled engine....using salt water
to cool it's innards...no heat exchanger
Being raw water
cooled means it does not run very hot at all....way cooler than an engine with a heat exchanger
. Don't expect to see high engine temps, because of this. This low engine temp is likely also the reason you might see an oily sheen on the water
, as the engine does not get hot enuff to burn all the fuel
..and as you say, hard to detect.
My engine also developed this " white smoke"....though I could never tell if it was smoke or just steam....read on...
The problem with these engines, that being raw water
cooled, the cooling
passages around the cylinders tend to get gummed up with salt
crystals/residue. The exhaust manifold is also raw water cooled and a common problem with these engines is that the exhaust manifold tends to " rust out" on the inside, from all the sea water, developing tiny holes inside, so what you are seeing is superheated steam that gets expunged with the exhaust gases. The problem starts to appear when the raw water cooling
passages around the two cylinders gets gummed up and this build a lot of pressure.
The " white smoke" was at first alarming to me, but I noted I was not burning any oil
, so it was not that.
I ran my engine routinely at around 2,200 rpm for hours without a hiccup.
I did make it a habit, to remove the cylinder head
to ream out the cooling passages. Then I simply replaced the head
with the original head gasket
. I must have done this at least a dozen times, always replacing the original head gasket
. Never had a lick of problem. Not once.
Never had a problem with the engine either, despite being nearly drowned in seawater on one occasion...just cleaned it out and it started right up.
Yes, the exhaust manifold and riser are the first place I would look for a problem, but also, don't forget to remove the cylinder head to ream out the cooling passages.
This engine is not made anymore, though I believe parts
are still available. Be prepared to sell your firstborn to pay for the parts
But, yeah, being an old cranky engine with a monster flywheel, it always started right up, never once did I have a problem starting it.
Clean up the water cooling passages and if you can find a replacement, get a new exhaust manifold and riser, and that thang will surprise you by running forever.