hi, all have a yanmar 2qm15 in c and c 32. engine rebuilt maybe 20 yrs ago bt PO. Hauled it yesterday for winter storage and just about made it in, I am suspecting a blown head gasket but not sure--- symptoms 1 for the past couple months have not been able to get to full power. Thought I needed to bleed system but decided to wait. 2 There is black discoloration on stern, above water line. 3 I have noticed oil in bilge, heavy. not diesel fuel after using motor. Engine starts ok , maybe 30 seconds or so before it catches, but then runs smoothly, just can not get much power. 4 Coming in yesterday to get hauled I looked back and saw a two three inch wide oil slick coming from boat, then it stopped. I think I may have tried to speed up just before the slick appeared, but not sure. May have seen black /white smoke for a few seconds. over the past month or so, but for less than 5 seconds. Sorry for the uncertainty, but I now am imagining I see every symptom I have read about. But, if I had to bet, I would say a few times it was black smmoke. I think it might be head gasket, but not sure how oil is getting out of engine into the bilge. Going over tomorrow to see if there are any tell tale signs. Also will check antifreeze as I have heard that blown gadket causes antifreeze to bubble. Also, will check dipstick as maybe there are tell tales of water in that. Thanks for any suggestions/a
advice on diesel symptoms-- head gasket blown?
- Thread starter dmcelwreath
- Start date
Check your mixing elbow. With the exception of oil in the bilge, all the symptoms described point to the mixing elbow.
If I remember correctly, the QM dipstick tube end is below the normal oil level in the sump and any build up of crankcase pressure will force oil out of the top of the tube.. make sure breather is clear.. Also, there is an external oil line on the aft port side of the engine. It has banjo bolt connections .. Look at the line and the three connections for leakage.. The line is steel and they sometimes will corrode through.
If the engine starts well, probably not a head gasket problem. A fouled propeller or dirty injectors may be the source of the smoke and low power, as well as Kappy's note about the mixing pipe.
If the engine starts well, probably not a head gasket problem. A fouled propeller or dirty injectors may be the source of the smoke and low power, as well as Kappy's note about the mixing pipe.
A blown head gasket would likely cause the engine to overheat as well as getting coolant into the oil pan. it really sounds like a mixing elbow problem not surprising after 20 years.
Had the same symptoms with my 3YM20. Thought it might be a fuel or injector problem. Changed out the mixing elbow and acid washed the heat exchanger and suddenly all was right with the universe. Also give the prop and bottom a look see. Doesn't take much to foul a prop.
30 seconds is excessive starting. 5 - 10 seconds on a stone cold engine which has not run for a month. The usual check through for voltages may be in order.
Are you hauled for the winter or only for short term work and back in? Testing the engine will be difficult if you're out for the winter and maybe best left until spring when you're back in again.
After years of careful observation, I have become aware that the diesel exhaust does not exit the vessel through the mixing elbow but leaves the engine in some other unknown fashion such as into the bilge or aft cabin. Otherwise, how can you explain this mixing elbow condition.
Even with the exhaust having an opening of roughly 1/4" dia, the engine still started normally and ran without a gross loss of power.
Ripley's Believe it or Not is still looking into it.
good advice , thanks. I am out for season, but I can run engine with a hose and bucket of constantly filling water. But I am thinking about suggestions. Prop is pretty clean. I agree that oil is coming out somewhere and getting to bbilge, did not know it could push thru dipstick, and I will check oil feeder hoses. I will check mixer elbow . Age suggests it is corroded, but would that affect compression? Also, on starting, The engine starts to catch in 5 seconds or so, but doesnt actually run smooth for another 10 or 15 seconds so I have to keep the starter engaged. It has been doing that for the last 15 years or so. And if it is warmed up, it starts right up. After reading your replies, I hope it is the mixing elbow, I dont think I will tackle taking the head off. Thanks to all. I may go over tomorrow to check out some things you suggested. Will let you know.
Always start with the simple (cheap) and work towards the more complex ($ $ $ $). On average, it's more likely to be the cheaper problems that are more common.
Excellent setup. Don't do like some people here and plug a hose into the cooling water supply and then wonder how the engine cylinders became flooded.
It's not the age that causes the problems but the blockage by carbon as shown in post #7. Neither of these problems affect compression.
Still doesn't sound right. Is this after a month or so of not running ? If so, try pre-lubricating for 5 seconds, repeated twice. Pull the stop cable and engage the starter for 5 seconds. Oil starts flowing at low RPM. Stop and wait for a minute. Repeat. Push the stop in and start normally. See if you fully start within 5 seconds.
If it is blocked or even partially blocked then, yes. That was my issue. It would be like putting a potato in the exhaust pipe of your vehicle. It would have a hard time starting if at all. The pressure increase is not letting the pistons to do their job easily. So, slow starting, smoke, higher temp. and inability to get to max rated rpms. That's this non-mechanic's take on it.
Regarding only your cold start issue: The 2QM15 is a peculiar engine. It has pre-combustion chambers without glow plugs. Usually engines with pre-combustion chambers have glow plugs. Hard cold starting is probably normal for this engine. I know it is with mine. That engine has a decompression lever attachment on the valve cover but was usually supplied to the boat builder without the control cable needed to utilize the decompression feature. That feature could help in cold starting and can be made functional in yours with the addition of a cable. Yanmar also made a "thermostart" device for that engine that can be installed in an existing port just behind the air cleaner. That device drips diesel into the intake casting and ignites it to warm the intake air and assist in cold starting. Look at tractor supply sites to purchase thermostarts. These items are bandaids for the cold start problem with the 2QM15. Yanmar only made this engine for a couple of years and in my opinion it may have been due to the cold start issue that it was discontinued.