Yanmar Woes

[Dockhead]

Here is one for people who understand marine diesels. My knowledge of them is completely inadequate for this situation. That would be fine, except that the same was true of the Yanmar engineer who looked at my boat. Now that is scary!

It all happened a couple of days ago when we were coming back across the English Channel from Cherbourg. Cherbourg to landfall at the Needles on the Isle of Wight is 000 magnetic. It’s now autumn so the weather is inherently turbulent, and wouldn’t you know it, North winds were forecast for the foreseeable days. Since the forecast was sunshine and Force 4 – 5, I decided to go for it – our boat is pretty weatherly and I thought we could just tack home.

It all started out pretty well but then the wind increased and increased until it was blowing a steady 25 – 28 apparent. At that wind force we are already pretty well reefed down and the boat gradually loses her ability to go to windward. So about 20 miles out as our VMG to windward continued to fall I decided to motor the rest of the way in.

I motored at 2800 RPM for about an hour, making about six knots bashing into the seas, when the power started to drop off. Then I noticed that I couldn’t rev over 2500. Temperature and oil pressure normal. I looked in the engine compartment and nothing seemed amiss, but the coolant level was down somewhat. I topped it off. There was a small oily mess in the bilge, which is unusual.

I decided it would be really dangerous if the engine failed completely so we put up sail and shut it down. I set a new course for Weymouth, to the West, and we settled in for a long night of heavy weather uphill sailing. We arrived about 01:00 and went to sleep.

The next morning, I started the engine (started instantly as usual), warmed it up, then ran it up out of gear. It would rev to only 3400 (normally will go to 4000 out of gear) and I thought I heard a grinding sound instead of the usual turbo whistle. My first thought was that the turbo is shot, which would explain everything.

I managed to find a Yanmar engineer who came over and looked over the engine. He took off the air cleaner and determined that the turbo was spinning freely and that intake side turbine blades were clean. There was oil coming out of breather which explained the small oily mess in the bilge.

We then ran the engine up again, and this time it ran normally. It revved happily to 4000 out of gear, turbo whistling away, and in gear ran up to 3800, churning up the water.

He poked around for a while longer. Then we ran it up again, and again it would not rev past 3400 out of gear.
He went home, consulted with the Yanmar distributor, and came back with this diagnosis. Unlikely to be a turbo problem, since the turbine spins to hand and the blades are clean (no oil from a blown seal or bearing). Oil coming out of the breather is likely to be a red herring – result of motor sailing heeled over the day before. Possibly head gasket or cracked head, which does happen sometimes with these engines. More likely – crack in the exhaust manifold.

His theory is that coolant is getting into the cylinders through the exhaust ports when the engine gets really hot. These manifolds (which cost 1500 pounds or $2400 – ouch!) do crack sometimes.

His proposal is to take off the manifold and have it pressure tested in a special high temperature pressure tester.

This just doesn’t seem right to me. How can coolant get into the cylinders from the exhaust manifold? This is a turbocharged engine, so the exhaust comes out into the manifold under a lot of pressure.

He admits that he is grasping at straws, and I just don’t like that, when every straw can cost thousands and not fix the problem.
Any of you diesel geniuses have any clues? Doesn’t it seem more likely that the turbo is misbehaving? Do turbos sometimes jam or seize when they get hot, only to free up when they cool off? That would explain why the engine ran well after he spun the blades with his fingers.

Any other ideas?

The engine is a Yanmar 4JH3HTE 100 horsepower made in 1999, 2000cc with turbo and intercooler. It has total 1030 hours on it, 200 of those put on by me over the last 13 months. When I bought the boat, with 830 hours on the engine, it was smoking heavily, and the seller did a lot of work (unsuccessfully) to stop the smoking – he had the injection nozzles cleaned, overhauled and calibrated the injection pump, had the turbocharger overhauled. The engine does not consume any oil (1/2 a liter in 100 hours) but does produce fuel smoke.

I will be grateful for your ideas!