Yanmar 3QM30H (fresh water) white smoke.

[Rmccormi]

Hello, I have a 1980 Yanmar which until recently has been running great without any issues. Let me explain, when I start the engine, no white smoke and very good water flow leaving the boat. Then after about ten minutes the amount of water leaving the boat visibly decreases and white smoke (maybe steam) starts to appear.

Because the boat is in salt water, I have a bypass at the water inlet seacock which allows me to place a fresh water pickup hose. When this hose is placed in a bucket, filled with fresh water, there is not the suction which I have experienced in the past to deliver fresh water to the engine.

I replaced the impeller this morning and the condition persists . I will be checking the thermostat next. Also I dove the hull recently and all is clean at the intake.

If I had limited water leaving the boat at start up, I would expect a clog in the hose leading to the pump. This still may be an issue.

Any thought would be appreciated, I am included to think I have a clogged mixing elbow?

Thanks and happy sailing

[Rmccormi]

Just a quick update, I let the engine cool some and started it to flush with fresh water. Since I had more suction at the raw water inlet than I did when the engine was brought to its operating temperature, I am inclined to think the thermostat is operating fine but once open water isn’t able to pass through the manifold or mixing elbow - would this cause back pressure so the pump would loose suction? Sorry the last sentence in my original post had the word included instead of inclined.

[Wotname]

ATM, I am a little confused by your description.

The 3QM30H (and 3GM30) were originally cooled with a direct raw water circulation i.e. no heat exchanger.

The 3QM30Y and 3QM30F were both cooled with coolant and a heat exchanger.

All the engines should have one and only one thermostat. The raw water cooled engine has the thermostat fitted in the exhaust manifold. The coolant cooled engine has the thermostat fitted on the side of the coolant tank.

Some (many?) 3QM30H engine's were modified to run a coolant cooling system and sometimes the modification was done poorly and left the raw water thermostat in place and well as fitting the coolant thermostat - bad practice.

All engines should have a constant flow and volume of water into the exhaust mixing point regardless of engine temperature.

In the coolant cooled engine, there is nothing in the raw water flow circuit that alters the raw water flow into the exhaust mixing point.

In a raw water cooled engine, the thermostat restricts the flow of raw water into the manifold when engine is cold and diverts the raw water directly into the exhaust. As the engines heats, the thermostat directs raw water into the exhaust manifold. It exits the manifold and goes it into the exhaust mixing point. Thus the volume of water entering the mixing point remains constant regardless of engine temperature.

If your engine has a thermostat in the exhaust manifold, check the internal water galley of the manifold as these do get badly clogged and can be a bear to clean. If badly clogged, the volume of water going into the mixing point will decrease.

[Rmccormi]

Wotname - thank you for the detailed information - much appreciated. The engine is raw water cooled. From your description. I assume that if the manifold internal water galley is clogged the raw water pump would not loose any efficiency?

[Wotname]

Originally Posted by Rmccormi

............. I am inclined to think the thermostat is operating fine but once open water isn’t able to pass through the manifold or mixing elbow - would this cause back pressure so the pump would loose suction? ..................

This is correct.

Additionally, if the volume of water exiting in the exhaust when the engine is cold is greater than the volume of water exiting the exhaust when engine is hot, then the injection point (mixing elbow) is most likely to be OK. The restriction to the flow must be occurring in the manifold, not in the mixing elbow.

Both should be inspected however.

Originally Posted by Rmccormi

Wotname - thank you for the detailed information - much appreciated. The engine is raw water cooled. From your description. I assume that if the manifold internal water galley is clogged the raw water pump would not loose any efficiency?

Sort of correct .

Put another way, the water pump could be 100% perfect (say brand new) but it still would not suck if the outlet (exhaust manifold water gallery) is blocked.

[Rmccormi]

Ugg, the manifold is a scary proposition since I am told Yanmar no longer makes the item for my engine. After market mixing elbows appear to be available. My intuition figured that the manifold is the culprit so my next step is to remove the manifold and mixing elbow for inspection. Thank you so much for the advice - very much appreciated!

[Wotname]

Originally Posted by Rmccormi

Ugg, the manifold is a scary proposition since I am told Yanmar no longer makes the item for my engine. After market mixing elbows appear to be available. My intuition figured that the manifold is the culprit so my next step is to remove the manifold and mixing elbow for inspection. Thank you so much for the advice - very much appreciated!

I could send you some horror pictures of a completely clogged up manifold that was terminal but I won't

Never fear, mostly they can be cleared enough to work OK. If it looks too difficult to clean, post some pictures of it here and the collective hive will step in to help as there are a few tricks we have learnt over the years to get them clean enough.

I have a 2QM20 in pieces (long term project) and if I finish it, I will have to make a custom manifold for it.

At the end of the day, if a 'thing' is made by man, it can be fixed by man.

[Rmccormi]

Thanks for keeping this adventure in perspective. Next week I will be back to the boat to remove the items, and will post some pics. Until then - more research[emoji41]

[Rmccormi]

Well got the manifold off and it appears the port, which I assume needs to be open for the engine water to circulate, is clogged. The balance of the manifold passages also has crud but isn’t as bad. On the exhaust side there doesn’t appear to be an excess of carbon.

[Wotname]

It looks reasonably bad but not terminal. I think it should clean up OK. The bottom gallery in the middle picture certainly needs cleaning. This gallery clogs up quickly - I assume because of decreased water flow and gravity.

Is there a drain point on the side of the manifold, my 2QM20 manifold had one and it was totally clogged and useless.

[Rmccormi]

Yes, the manifold does have a drain point which I also expect is clogged. I am surprised the thermostats worked - they too were clogged.

Thanks for you help, much appreciated!

[Rmccormi]

I am assuming the engine water has to flow past the thermostats? My red arrows indicate water flow - sorry for the poor exhibit (need smaller fingers)

[Rmccormi]

Wotname, finally got the manifold cleaned up, pulled a lot of gunk out of the core. I expect the thermostats also restricted the water flow, in fact they might even have been the culprit.

Regarding the mixing elbow, I bit the bullet and ordered a new one from HCI Marine.

My next step is the utilize a small bilge pump to flush the engine. I utilized Rydlyme Marine for cleaning the manifold and expect it will also work on the engine. Of course I will remove and plug the three engine zincs .

Thanks for your support[emoji41]

[Wotname]

Wow, well done! The manifold has come up looking good.

[Rmccormi]

Originally Posted by Wotname

Wow, well done! The manifold has come up looking good.

Finally got down to the boat, flushed the engine, installed the manifold, new water hoses, and exhaust hose. Started the engine and it seams to be very happy! Again thanks for your support [emoji41]