When thermostat starts cycling at higher power settings in
warm summer water is this an indication of the exchanger
clogging? Have heard that you can use carbolic acid treatment
to clean out, but am reluctant to do so. Any suggestions
about unclogging without removal of the exchanger? Had the
heat exchanger done by shop maybe some ten years ago, guess
might be time to have done again. Would like to try myself
so welcome any suggestions or maybe other sources that might
cause this problem....Cape Dory 30k sailing from Atlantic
Beach NC......
Sailonthesea@aol.com
Heat exchanger volvo MD7A
Moderator: Jim Walsh
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mike m
Re: Heat exchanger volvo MD7A
Hi Jim ...I also like to know how it worked out with others...Jim Lewis wrote: When thermostat starts cycling at higher power settings in
warm summer water is this an indication of the exchanger
clogging? Have heard that you can use carbolic acid treatment
to clean out, but am reluctant to do so. Any suggestions
about unclogging without removal of the exchanger? Had the
heat exchanger done by shop maybe some ten years ago, guess
might be time to have done again. Would like to try myself
so welcome any suggestions or maybe other sources that might
cause this problem....Cape Dory 30k sailing from Atlantic
Beach NC......
I was about to try it out then chicken out ...thought maybe will screw up gaskets and what not with the inroduction of acid...but some time ago someone mention some other type of fluid available for unclogging the inner works/ducts of the exchanger...look into past bulletin inputs....
I am about to pull the whole thing apart and rework the exchanger......
like to see a better/simpler solution...
cheers/mike m
compinchecd30@yahoo.com
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Dale W
Re: Heat exchanger volvo MD7A
Good questions. The first question in my mind is how strong and regular is the water flow out the exhaust? Good water flow is essential but can happen with some internal clogs.
Since my MD7A is raw water cooled, and I'm assuming yours is, too, then we are talking about the exhaust manifold - not, I believe, a heat exchanger. . .
I've disassembled my exhaust manifold regularly. I'm just down the road in Jacksonville, NC, and keep my boat on the New River (shallow and lots of mud and silt) hence frequent cleaning out.
So, the job is not technically hard or tricky. I do try to keep track of which bolt comes out of which hole. I bought a new set of gaskets before the first time I tried this. I still have them. I use the blue Permatex Hylomar hpf gasket dressing and flange sealant on all surfaces as I reassemble the pieces.
Working from the cabin access (if you truly enjoy suffering you can make it a lot harder by crawling into the port locker and hunkering in there), the basic sequence is to:
- disconnect the copper tube from the top of the water pump.
- remove the hose coming from the back of the manifold to the water cannister.
- pull the wire plug off the heat sensor (lower rear of manifold).
at this point, the manifold, thermostat, copper tube inlet assembly is isolated from the rest of the engine.
- unbolt the 4 bolts attaching the water cannister.
- reaching down the side, unbolt the 4 bolts holding on the exhaust manifold. I usually do the bottom ones first because the manifold will drop a bit when the last one comes out.
The manifold assembly can then be worked around and removed.
Potential problem areas:
- thermostat housing (the end piece with 2 bolts). Mine tended to dissipate (like you could dig it out with a knife blade). Because this housing channels the water through an internal passage it is bad for this metal to disappear. The good Volvo folks wanted $195 for this 10 dollar piece of pot metal, so I dug out the bad stuff and repaired mine with epoxy.
- the thermostat itself can go bad. Stick it in hot water and watch it open (do this on the stove in a pan when your wife is not watching, unless you want to be treated like an 8 year old doing an illicit science experiment.) Don't worry too much about how it looks, just how it moves in hot and cold water.
- The exhaust manifold and engine block passages. You can dig some stuff out, but they will probably look pretty good. There's one small passage in the center top area that usually needed dug out on the block side.
So then,
- it's all apart, it's cleaned up, nothing is obviously screwed up.
- it's time to reassemble. Use the Permatex blue stuff and rub it on each surface. Get the thermostat in and the copper inlet tube attached.
- rub some blue stuff on the engine block surface and the manifold surface and both sides of the manifold gasket.
- Stick the gasket to the manifold.
- Work the manifold assembly back into place. Don't worry if the gasket slips a little. Once it's about right, slide in one of the top bolts.
- Get the threads started in the block, and then get the other ones started.
- Use some blue stuff on the flange to the water cannister and get all four bolts started to reattach. (Note some different length bolts, maybe?)
- Once all the bolts are started, snug them all down. I usually do the manifold first and then the flange.
- do a final tightening.
- reconnect the hoses, copper tubing, and heat sensor wire.
Now the fun part is to crank the engine and see what happens. Hopefully, you see nothing and every thing is normal and the engine pumps water and the gauge indicates that all is well. . .
or -
water drips. This is most likely from the one of the ends of the copper tubing going into the manifold. Given that the components are ok, and you used some blue gasket dressing, it is probably fixable by just pushing and realigning the tubing.
Good luck, Dale
(If you're interested, drop me an e-mail maybe we can get together.)
majortes@earthlink.net
Since my MD7A is raw water cooled, and I'm assuming yours is, too, then we are talking about the exhaust manifold - not, I believe, a heat exchanger. . .
I've disassembled my exhaust manifold regularly. I'm just down the road in Jacksonville, NC, and keep my boat on the New River (shallow and lots of mud and silt) hence frequent cleaning out.
So, the job is not technically hard or tricky. I do try to keep track of which bolt comes out of which hole. I bought a new set of gaskets before the first time I tried this. I still have them. I use the blue Permatex Hylomar hpf gasket dressing and flange sealant on all surfaces as I reassemble the pieces.
Working from the cabin access (if you truly enjoy suffering you can make it a lot harder by crawling into the port locker and hunkering in there), the basic sequence is to:
- disconnect the copper tube from the top of the water pump.
- remove the hose coming from the back of the manifold to the water cannister.
- pull the wire plug off the heat sensor (lower rear of manifold).
at this point, the manifold, thermostat, copper tube inlet assembly is isolated from the rest of the engine.
- unbolt the 4 bolts attaching the water cannister.
- reaching down the side, unbolt the 4 bolts holding on the exhaust manifold. I usually do the bottom ones first because the manifold will drop a bit when the last one comes out.
The manifold assembly can then be worked around and removed.
Potential problem areas:
- thermostat housing (the end piece with 2 bolts). Mine tended to dissipate (like you could dig it out with a knife blade). Because this housing channels the water through an internal passage it is bad for this metal to disappear. The good Volvo folks wanted $195 for this 10 dollar piece of pot metal, so I dug out the bad stuff and repaired mine with epoxy.
- the thermostat itself can go bad. Stick it in hot water and watch it open (do this on the stove in a pan when your wife is not watching, unless you want to be treated like an 8 year old doing an illicit science experiment.) Don't worry too much about how it looks, just how it moves in hot and cold water.
- The exhaust manifold and engine block passages. You can dig some stuff out, but they will probably look pretty good. There's one small passage in the center top area that usually needed dug out on the block side.
So then,
- it's all apart, it's cleaned up, nothing is obviously screwed up.
- it's time to reassemble. Use the Permatex blue stuff and rub it on each surface. Get the thermostat in and the copper inlet tube attached.
- rub some blue stuff on the engine block surface and the manifold surface and both sides of the manifold gasket.
- Stick the gasket to the manifold.
- Work the manifold assembly back into place. Don't worry if the gasket slips a little. Once it's about right, slide in one of the top bolts.
- Get the threads started in the block, and then get the other ones started.
- Use some blue stuff on the flange to the water cannister and get all four bolts started to reattach. (Note some different length bolts, maybe?)
- Once all the bolts are started, snug them all down. I usually do the manifold first and then the flange.
- do a final tightening.
- reconnect the hoses, copper tubing, and heat sensor wire.
Now the fun part is to crank the engine and see what happens. Hopefully, you see nothing and every thing is normal and the engine pumps water and the gauge indicates that all is well. . .
or -
water drips. This is most likely from the one of the ends of the copper tubing going into the manifold. Given that the components are ok, and you used some blue gasket dressing, it is probably fixable by just pushing and realigning the tubing.
Good luck, Dale
(If you're interested, drop me an e-mail maybe we can get together.)
majortes@earthlink.net
-
Carl Jones
Re: Heat exchanger volvo MD7A
Jim,Jim Lewis wrote: When thermostat starts cycling at higher power settings in
warm summer water is this an indication of the exchanger
clogging? Have heard that you can use carbolic acid treatment
to clean out, but am reluctant to do so. Any suggestions
about unclogging without removal of the exchanger? Had the
heat exchanger done by shop maybe some ten years ago, guess
might be time to have done again. Would like to try myself
so welcome any suggestions or maybe other sources that might
cause this problem....Cape Dory 30k sailing from Atlantic
Beach NC......
I moved my heat exchanger to the port cockpit locker to make it easier to get to and service. I clean mine every season. Its easy now that I moved it. I take it out and clean it out with muriatic acid and rod it out with a coat hanger. We get these little clams that grow in there down here in Texas. However, I always see the temperature run higher in the summer time when the bay water temperature gets up in the 80's. My heat exchanger is a Sendure model and I think it is also a little undersized. Its only about as big in diameter as a coffee cup, and maybe 12" long. I can't run the engine at full rpms in the summer without it reaching the edge of the red zone on the guage. I recommend you learn to clean it yourself as it could save the day. It's not rocket science so wade in and try it.
Good Luck,
Carl Jones
s/v Spanish Eyes, CD30 Cutter
Gulf Coast Fleet
GreatCells@aol.com