md7a losing power & cutting out

[jkishel]

That's right, I forgot that it restarts so it's probably not air. Also, I was focused on the apparent overheating. But this is an exhaust temp alarm, not a coolant temp alarm. If it sounds only after the engine dies, it is possible that the engine isn't overheating at all. The exhaust manifold temp rises as cooling water flow stops when the engine shuts down, then the alarm sounds. Not sure why the alarm doesn't sound every time the engine is shut down unless it is wired into a run circuit that you turn off before you kill the engine normally. Anyway, if the engine isn't actually overheating, this sounds like a fuel issue. If it is truly boat motion related, I'd suspect the tank, fuel pickup and/or primary filter as places where crap or water could be shaken up. Because the engine restarts after awhile and it's the easiest thing to do, I'd replace the fuel filters first (classic symptom of restricted primary is engine dies but can be restarted after awhile) and see what happens.

[spraoi]

Yes it's possible the engine isn't overheating at all, just the exhaust. The alarm is wired to the main electrical isolating switch for engine which we don't always turn off straight after engine shutdown. As I've said before I cleaned the tank and fuel lines last year but dirt or water could have gotten in since even though there's no sign of water in the primary. The filters aren't due a change but I'll go ahead and change them anyway.

For now we'll just pick and choose harbours we can sail in and out of!

And deepfriz thanks, she's a great boat indeed.

[jkishel]

Good luck and fair winds!

[Shawn67]

“There appears to be the same volume of water coming out of the exhaust exit as usual but it's hard to be certain.”

This actually means nothing in the MD7A. The cooling system moves from the pump to the hard pipe that goes two places. One is into the exhaust manifold and from there into the head and block then back into the exhaust manifold at the thermostat then into the thermostat housing and out to the exhaust. The other section of the pipe from the water pump is just a bypass that feeds directly to the thermostat housing (behind the thermostat) and out the top to the exhaust. It is possible the feed into the block is clogged and if that happens the pump will just keep pumping through the bypass and into the exhaust. With my fresh water conversion I’m actually reducing the flow through the bypass as it is not needed to keep the exhaust cool, that will be done by the new raw water cooling circuit.

“Might it be necessary to install another raw water pump to boost the cooling water through engine?”

No, you are getting clogged up. The passages are small and clog pretty easily. Once you start overheating it gets worse and worse quickly as you get above the point where the salt starts crystalizing and it clogs more.

“As for air would the fuel system not need to be bled to restart the engine?”

Yes, the MD7A isn’t self bleeding. I have/had a small leak in #2 injector and once it gets air in it it will not fire/run until bled again.

Shawn

[Shawn67]

"Sure would be nice if your kill switch was hooked up to it (grin)."

The MD7A doesn't have a kill switch. It is a cable connection to the high pressure fuel pump that shuts off all fuel flow. The MD7A is very basic electrically. It doesn't need an electrical system at all to start or run it.

Shawn

[Shawn67]

If you check out this thread you can see pictures of how the ports clog up between the exhaust manifold and the head...

Volvo MD7A Overheating Solved? - SailNet Community

This is pretty much what mine looked like too when I opened it up.

Shawn

[Shawn67]

"I'm sailing in Carribean now so access to parts is limited."

Wanted to mention if you are careful you may be able to reuse the exhaust manifold gasket if you don't have access to a spare. You will likely need replacement square O rings for the hard pipe connections at the water pump, under the exhaust manifold and to the thermostat housing. If you open the thermostat housing there is a large gasket around the thermostat and a small O ring in there. Next time you have access to a West Marine they sell a complete kit of all those cooling system gaskets for about $10.

If you have access to an IR thermometer (or really almost any contact thermometer) try checking your manifold/head temp to really understand if you are overheating or not. The thermostat is a 140 degrees in the Volvo. If you are seeing much above that at the exhaust manifold you are probably clogged.

Shawn

[spraoi]

Hi Shawn67

Thanks for all your advice, I'll take it onboard. Excuse the pun! The first thing for us to do is get the ir thermometer to confirm the engine is actually overheating.

Thanks everyone for your replies, we'll let you know how it works out in the next couple of weeks.

[spraoi]

Hi all

I changed primary and secondary fuel filter before trip from Curacao to Panama as Jkishel advised.We hit head winds and 2ft cross swell on last day of sail.So we motored at low rpm then and were rolling around alot. After 12hrs we got in to harbour with no engine problems and a big sigh of relief.We broke our goose neck 1st night out but thats another story :-)

So hopefully after all that the filters were probably the issue. Still no idea why the exhaust overheat alarm went off.This is why I thought it was more than a fuel problem.

Got the ir thermometer here and ran engine at high rpm as Shawn67 advised it got up to 87 degrees celcius/188.6 degrees f at hottest point on manifold.This is a bit above the 140f Shawn67 said was correct temp.Not sure if this is too much above normal?If so I'll have to open up manifold and clean it out a job I dont look forward to.Thanks.

[jkishel]

Great news on the fuel front, but 180 is too hot if you're measuring temp on the block and head. The cooling water should be no more than 140F. Basic troubleshooting - check through hull, hoses, strainer, impeller, thermostat and mixing elbow.


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[Shawn67]

Yeah, if you are 188 degrees on the exhaust manifold you are way to hot for a raw water cooled engine. The exhaust manifold should always have a small amount of flow through it (even when the thermostat is closed) so it doesn't get to hot.

If you are that hot (and you still have good flow of water out the exhaust) your troubleshooting is pretty easy... you have a clogged exhaust manifold which is also meaning it is blocking flow into the head/block. At those temps it is going to continue to build up more and more salt deposits inside and get worse and worse.

Gonna have to pull off the exhaust manifold and clean it all out. My exhaust manifold runs around 120-130 degrees now after cleaning it all out and converting to fresh water cooling. And that is with a 170 degree thermostat, I think I have a little blockage in my engine bypass which is causing the overcooling. I need to pull my thermostat housing and check that.

Shawn