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Old 26-10-2010, 07:35   #1
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Yanmar Woes

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!
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Old 26-10-2010, 07:49   #2
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The Turbo has nothing to do with the pressure the exahust exits the head at. 99% of the time when a turbo fails catastrophicly you'll have black smoke and very little power but they can fail slowly.
However when a manifold does fail you'll not likely see coolant back in the engine it will dissapear from the tank, but not find it's way into the engine unless you shut if off hot, with the valve open on the cylinder that has the crack in the manifold. How did he check the turbo? just by spinning or by measureing end play(horizontal) and vertical movement. These little turbo's spin upwards of 35,000 RPM the bearings must be within tolerance or the shaft will wobble and prevent the turbo from ataining full rated speed. Beyond that, check the compression......it's the cheapest and fastest thing to do.
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Old 26-10-2010, 08:42   #3
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Check for blockage in the exhaust elbow. I had a similar problem years ago and after much head scrtching, the Yanmar rep told the mechanic to check for blockage in the exhaust elbow.
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Old 26-10-2010, 10:01   #4
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I've had a cracked manifold on a turbo motor do exactly as you describe.
Have the tech pull the turbo for a visual inspection of the exhaust side.
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Old 26-10-2010, 10:30   #5
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I guess you ckd fuel filters,when rough stirs up tank.marc
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Old 26-10-2010, 10:34   #6
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if it has been 1000 hours then check the exhaust elbow to make sure it is clear. you can remove the hose and look up into it but may need to replace hose after that.
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Old 26-10-2010, 10:41   #7
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It's a diesel, if it starts to sputter, it's the fuel. I started to loose power going under a bridge in the ICW yesterday, dropped anchor in a dicey spot and quickly changed all my fuel filters, they were all gummed up. In rough weather all kinds of stuff gets churned up in the fuel tank. Spent this morning doing the oil and the genset. Toot toot.
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Old 26-10-2010, 15:38   #8
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Originally Posted by never monday View Post
I've had a cracked manifold on a turbo motor do exactly as you describe.
Have the tech pull the turbo for a visual inspection of the exhaust side.
Hi, thanks. Will we be able to see evidence of coolant getting into the exhaust on the exhaust side of the turbo?
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Old 26-10-2010, 15:42   #9
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Originally Posted by Sailmonkey View Post
The Turbo has nothing to do with the pressure the exahust exits the head at. 99% of the time when a turbo fails catastrophicly you'll have black smoke and very little power but they can fail slowly.
However when a manifold does fail you'll not likely see coolant back in the engine it will dissapear from the tank, but not find it's way into the engine unless you shut if off hot, with the valve open on the cylinder that has the crack in the manifold. How did he check the turbo? just by spinning or by measureing end play(horizontal) and vertical movement. These little turbo's spin upwards of 35,000 RPM the bearings must be within tolerance or the shaft will wobble and prevent the turbo from ataining full rated speed. Beyond that, check the compression......it's the cheapest and fastest thing to do.
Thanks very much for this.

One question has been bothering me -- what are the possible failure modes of the turbo?

If it just seizes up, I understand there will be black smoke and very little power.

But short of seizing up -- can it fail partially or intermittently so that the turbine starts dragging and not spinning up to full speed?

If it were doing that when quite hot, then that would really explain everything.

I thought I heard a mechnical grinding sound in place of the turbo whine, too, on one of the run up attempts where the engine would not rev past 3400.

Can a check of the bearing tolerance reveal such a condition?

And what about the coolant loss -- the turbo is liquid cooled -- could coolant be getting out around bad turbo bearings or seals?

Thanks a lot.
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Old 26-10-2010, 15:44   #10
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Thanks everyone for the thoughtful replies.

It sound like I need to do something like this:

1. Eliminate potential fuel problems first of all. Change out the fine filter and bleed the system.

2. The turbo is still a prime suspect. Find some way to diagnose it.

3. Check for exhaust elbow blockage.

4. If none of this bears fruit, then pull out the exhaust manifold and have it pressure tested at high temp as the engineers suggested.

Anything else? Does that sound about right?
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Old 26-10-2010, 16:51   #11
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I guess you ckd fuel filters,when rough stirs up tank.marc
My very first thought. I have experienced just that.

Change both the Racor and on the engine.

Best $55 you will ever spend.
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Old 26-10-2010, 17:16   #12
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K.I.S.S. never over look the obvious... fuel , and fuel filters. run it off a jerry can through new filters with fresh diesel then you can look at everything else
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Old 26-10-2010, 19:37   #13
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Hi, thanks. Will we be able to see evidence of coolant getting into the exhaust on the exhaust side of the turbo?
yes you should be able to
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Old 27-10-2010, 02:23   #14
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yes you should be able to
Great; thanks. So the purpose of that test is to see if coolant is streaming into the exhaust tract through, say, a cracked manifold, right?

That sounds good and a lot cheaper than pulling the manifold off to pressure test it.

Do you think it is possible that the turbo bearings are failing partially, so that they start to drag when the engine is over a certain temperature?

Do you think I will be able to diagnose the turbo bearings with a micrometer as others have suggested?

Thanks a lot.
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Old 27-10-2010, 05:26   #15
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Great; thanks. So the purpose of that test is to see if coolant is streaming into the exhaust tract through, say, a cracked manifold, right?
the turbo has to be removed to remove the manifold. If there is a large enough crack you will see a trace of coolant. It may or may not prove anything.

Quote:
Do you think it is possible that the turbo bearings are failing partially, so that they start to drag when the engine is over a certain temperature?
I've never seen a turbo behave that way. When the bearings fail, the seal is compromised, then it pushes oil into the turbine or compressor.

Quote:
Do you think I will be able to diagnose the turbo bearings with a micrometer as others have suggested?
that's the directions in the shop manual :shrug: It must be an effective course of action.
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