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Old 09-02-2010, 14:37   #1
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Yanmar 3HM Overheating

Hey folks,

Sorry for the length...

I purchased and moved onto my sailboat just over a year ago, and have slowly been going through each and every system, learning it top to bottom. Finally I have tackled my engine - and just in time, as she had stopped running.

The previous owner apparently had a breakdown somewhere; he blew out his fresh water impeller and overheated, burned a hole in his water trap, and had to make modifications to get home. He rerouted the raw water intake through the main engine - not that bad a thing, apparently, the instructions on how to do this are in the service manual.

I left the engine this way for a year, not knowing any better. She ran pretty well for the year, though near the end of the summer she started giving off a fair amount of white smoke after running for more than a few minutes at a time. I stuck around an anchorage for a few months without moving, but then when I tried to move, she made it a few hundred meters and died and then wouldn't start again.

In an effort to get on top of the engine, I took a marine diesel theory class, and paid attention - when she stopped starting, I tracked down the problem to a plugged-up fuel lift pump, with no filter before it?? I rebuilt the lift pump, added a second filter and rerouted the fuel lines. She started!

When I went to move further, with the "repaired" engine, I made it about a kilometer before there were alarms and smoke, and I found I had overheated and burned out the exhaust line and burnt a hole in the new watertrap.

I got a new water trap, and examined the problem - water clearly isn't reaching the exhaust. So, I got a new exhaust elbow, replaced the impeller, and verified that the water flowed through - it was flowing well, the water trap was filling (and exhausting), and so I reassembled and moved on.

I made it another kilometer, but then there was smoke and alarms again - I had burned yet another hole in my exhaust - at least I caught it this time before it burned out the water trap! The only thing I can think of is that perhaps once the thermostats kick in, they're blocked somehow? I changed out the thermostats - they were corroded but seemed to open when I dropped them in hot water, though they never quite closed completely. I also changed the zincs, which were completely gone.

(in between here, I also did a lot of other neglected routine maintenance - changed the oil, changed the oil filter, new air filter, new fuel filter elements, etc - the basics.)

I haven't tested hard since changing the thermostats, but I have a hypothesis - I think that the block is getting too hot, and the white smoke is steam from the little water that is getting through boiling. I think that this could be caused by calcium scale building up in the block, preventing water from flowing through properly, especially with thermostats that were only partially working. I have done a bunch of googling, and apparently my options to get rid of calcium and rust buildup in the block are to either use muriatic acid - which I would prefer not to, given the nasty, toxic nature of the stuff! - or a less-harmful boiler descaler like Marsolve or Rydlyme.

I have not been able to find Marsolve or Rydlyme locally, so currently my next step is to purchase a large bottle (or two) of C-L-R, which I think will do the trick. After this, I intend to flush the block out completely with fresh water, reinstall the newly-rebuilt fresh water pump, drain the block and reinstall the cooling loop with the unused heat exchangers.

Before I run out and buy the C-L-R, does anyone know what the total coolant capacity of the Yanmar 3HM is? Has anyone had experience with using C-L-R to clean out calcium buildup in an engine block?

Any comments otherwise? Does what I am doing sound reasonable? This is my first engine, ever - up until this year the closest thing I've done to any of this is checking the oil on my dad's old Buick... I'm gaining confidence, but I'd definitely like to hear some more opinions...
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Old 09-02-2010, 15:38   #2
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There's products made especially for flushing cooling systems and engines available at all auto parts stores. Get the stuff for "severely neglected cooling systems." You put it in and fill the system up with water, then let it run. Then you drain it, fill with water again, and repeat until what you drain is clear.

It's usually suggested that you check/change the thermostat after this treatment because the lime/rust that breaks free can clog the thermostat.

It also never hurts to pull any petcocks you have on the block and back flush the system with the hose. That usually helps knock loose all the sediment sitting in the bottom of the block.

I just don't think CLR is going to be strong enough to get the rust out. It's fine in the shower when you can scrub with it, but inside the water passages of the block, you're completely relying on the strength of the chemical to eat away all the crud for you.
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Old 09-02-2010, 15:43   #3
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When you disconnect the waterline on your exhaust elbow...do you have water coming out?

I am betting a dollar to a donut that you have burned out a vetus waterlift?
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Old 09-02-2010, 15:49   #4
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Quote:
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When you disconnect the waterline on your exhaust elbow...do you have water coming out?

I am betting a dollar to a donut that you have burned out a vetus waterlift?
Hah, nice - actually, it's a Vetus WaterLOCK, but damned close!

If I throw the decompression lever and run the engine off the starter for a few seconds, I do get water out of the hose that leads to the exhaust elbow - but if I run the engine hard for a few minutes, I don't get water anymore, and after shutdown the waterlock is empty...
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Old 09-02-2010, 15:56   #5
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Square one.....

Pull the hoses off of the raw water pump and check for broken impeller pieces.

Check the pump for lodged pieces

Follow the trail all the way to the engine......Usually you will find a broken vane lodged in there somewhere.
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Old 09-02-2010, 16:02   #6
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Square one.....

Pull the hoses off of the raw water pump and check for broken impeller pieces.

Check the pump for lodged pieces

Follow the trail all the way to the engine......Usually you will find a broken vane lodged in there somewhere.
Hmm - well, I did check and replace the impeller in that pump, though there were no missing vanes.

...you do have a solid point though, I have no idea whether or not the prior owner lost some vanes. I will check all the hoses.
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Old 09-02-2010, 19:20   #7
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What has probably happened is that by routing the raw water (salt water) through the main engine has essentially turned the engine into a raw water cooled engine. If this has been done without replacing the original thermostat in the engine then the engine has been running too hot for a raw water cooled engine and the salt has come out of solution and been deposited on the internal surfaces of the engines cooling passages and blocked the circulation.

A fresh water cooled thermostat maintains the engine coolant at about 185F wheras a raw water cooled thermostat maintains no more than 135F ( less than the temp at which salt comes out of solution)
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Old 09-02-2010, 20:33   #8
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What has probably happened is that by routing the raw water (salt water) through the main engine has essentially turned the engine into a raw water cooled engine. If this has been done without replacing the original thermostat in the engine then the engine has been running too hot for a raw water cooled engine and the salt has come out of solution and been deposited on the internal surfaces of the engines cooling passages and blocked the circulation.

A fresh water cooled thermostat maintains the engine coolant at about 185F wheras a raw water cooled thermostat maintains no more than 135F ( less than the temp at which salt comes out of solution)
This agrees pretty much exactly with what I think is happening.

The big question is - what's the best way to unblock the cooling passages?
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Old 09-02-2010, 21:31   #9
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Two chemicals, both cheap and neither harmful in the quantities and dilutions that you will be using. The first is HCL (muriatic) and the second is oxalic acid.

Pull the thermostat out, disconnect all the hoses and plug off, except for a fill point at the top of the engine. Use a dilute solution of muriatic, fill the block and let it set for 30 minutes. Drain by the lowest point on the block, getting all the drains open and flowing. Flush with clean water.

Do the same with the oxalic.

Keep repeating this process until clean. You can find a couple of points (such as the thermostat housing where you can check how well all is doing. You may break some bigger chunks loose: Make sure that they get flushed out.

Clean water will neutralize the acid but if you are paranoid dissolve a little soda ash or bicarbonate in water and use that to kill any acid residue.

Now you can figure out what else is wrong with your engine but salt build-up in the cooling jackets is no longer the problem.

Done correctly this will not harm the engine. It is a recommended maintenance procedure for many raw water cooled engines.

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