Hi Jim / Chuck I would absolutely look at the elbow. I replaced pretty much everything on my 3GM30F's cooling system except the heat exchanger chasing cooling issues and the main culprit was the elbow, which eventually was 100% obstructed. The added pressure in the system caused my aging hoses to fail and ultimately killed the water pump too.
Oh and BTW, mine had a very small exhaust leak / hairline fracture that was impossible to see because it's on shower side. The leak caused some hard to explain smells (I had replaced all the exhaust hoses a couple years prior). Also, my wife sometimes had headaches after spending time in the cabin as she was getting stuff put away while we were motoring home back to the marina... I'm glad the whole system is now fresh (Parts weren't too expensive) and optimal but I could have saved myself some $$ and headaches if I would have looked at the elbow first. I didn't / looked at it last because all the "experts" told me not to worry about it. It seems like a really hard job to get the rust seized elbow off the riser on our boats (I have a 1990 34+, same boat as yours) and yes, it's nearly impossible. The good thing is: You don't have to. Just remove the riser off the exhaust manifold, that's an easy 3 minute job removing 2 bolts. I bought a new riser along with the new elbow for almost nothing getting one as a take-off (They "come with" the engine install kit and many engines no longer need it / the installers are happy to get rid of 'em). I gladly tossed the whole rusted-up assembly. Even if the elbow "looks fine" from the outside: sediments / carbon deposits / heat / gravity will plug it up. "Better" stainless elbows plug-up the same way. Fan back-up is not necessary (I live in Georgia where it hits over 100 degrees in the summer, never a problem with a properly working system) 2800 RPM is optimal cruising speed according to Yanmar and the engine Dyno sheet. I run it at a minimum of 2800 RPM and run it in the 3200-3400 range (Wide open or close to it) regularly. The engine is a 900cc 3 cylinder unit making 27-29 hp pushing ad 6+ton boat though the water. It needs RPM to do that and is designed as a "High Revving" engine (By diesel standards). The 3GM30F really is different from the larger 4 cyl Universal and other units often seen on similarly sized boats, they are happy to rev 1800-2100 all day, ours isn't and the transmission / prop pitch are not geared that way either. My engine was known as "Hard Starter" by the local mechanics, it was quite recalcitrant to deal with at any weekends' initial start when I first got it. (P.Os were a bit to "easy" on it and it was fouled-up inside) After a season of harder running / steady diet of Diesel Kleen additive it became much smoother and starts within seconds instead of what used to be a 10-15 minutes fight on Friday nights / Saturday mornings the get the bi$ch going. You should see 7.0 knots or so top speed at 3400 rpm's if your hull is clean. If you don't then clean your hull and check your prop pitch. It's possible some P.O over-propped it (Over pitching seems to be frequently advised by prop vendors, it's no good for our setup). Both can be complicit in causing over-heating issues. Finally, it's possible that the steam you see is just a fact of life in your neck of the woods. I see a fair amount of steam on my boat when we use it in the cooler months (We sail all year long). I would check the Elbow no matter what though, it's a 5-10 minute job using the riser trick. Best of luck with the project / contact me off list if you need more details. -Francois Rivard 1990 34+ "Take Five" Lake Lanier, GA On Behalf Of James Bibb via CnC-List Cc: James Bibb Subject: Stus-List Yanmar 3gm Ventilation OK?engine seems to run warm/hot?temp is not above 180 but I?m not running at 3,000 RPM, usually 2800. ?couple of questions?. Lot?s of steam out the exhaust which I believe is more do to the balance of coolant water in either muffler or the mixture elbow. I sometimes remove the engine access panels on either side and I notice an easy 5-10 degree drop in temperature from the gauge. I?ve checked the coolant, impeller, heat exchanger for clear and the thermostat last year. Haven?t checked past the coolant elbow or into the muffer. Does anybody have any experience and does anybody introduce a fan back-up cooling system into the engine compartment and if so how do they and where do they vent on a sailboat through the hull or deck? Does the steam indicate overheating or based on temperature am I running fine? Other question, what RPM do folks run their engine at for cruising speed? James Bibb SV Darwin?s Folly 1991 C&C 34/36R Juneau, Alaska
_______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
