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Old 04-03-2014, 06:16   #1
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3HM35 Yanmar stalls under load. What next?

One of the Yanmar 3HM35F's that we have is giving me problems. It starts fine, and runs a little rough for a few minutes with some white smoke, but smooths out and the smoke goes away after a few minutes. Very warm sea water here.

The problem is that when I am maneuvering while in a marina I can't keep the engine running while shifting from forward through neutral and to reverse, or vice versa at low RPM. It seems as though the sudden load of the prop is stalling the engine, as though it's not putting out full power. This only happens at low RPM, which at the moment is an idle around 800.

I found and replaced a banjo bolt on the fuel return line, which didn't do anything to help of course. That was when I took the injectors out and had them tested. They're fine. They were rebuilt recently, too. Next step was to check the thermostats, and I found both of them frozen in a partly open position. There are two on this engine. I replaced those with working thermostats, which made the white smoke go away much sooner after starting, but didn't do anything for stalling under load.

I removed the rocker arm cover and adjusted the six valves. They were a little loose but not by much. No change in performance.

I noticed that the engine does marginally better when I run it without the intake "silencer", which I'd call an air cleaner. So I washed out the conical foam element, and it's clean. Still stalls.

I took a look inside that tube where the water joins the exhaust in the mixing elbow, and it was constricted but not blocked. I opened it up with the tip of a screwdriver. Didn't change anything. I didn't take the hose off and look up inside it from the other end, yet.

This engine ran well for the trip down here, so I know it must have all it's major injector components installed. or assume so. These problems have developed gradually until recently it's become every time I try to engage it in gear at idle.

What's my next step? Governer idle? Take off the head and look for piston ring issues? If I had a broken or stuck piston ring, wouldn't the smoke tell me that?

I know I'll get up to speed on these old engines eventually, but could sure use some experienced advice in the meantime. Thanks for any help.
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Old 04-03-2014, 06:40   #2
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Re: 3HM35 Yanmar stalls under load. What next?

Continue your exhaust restriction investigation... elbow to hull...

Prop? Fouled?

Restricted or BAD fuel?

Can you bump the idle 100 rpm?
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Old 04-03-2014, 06:50   #3
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Re: 3HM35 Yanmar stalls under load. What next?

This may soubd stupid as you obviously know more about engines than I do, but why don't you increase the idle speed a bit?

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Old 04-03-2014, 07:01   #4
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Re: 3HM35 Yanmar stalls under load. What next?

This may soubd stupid...

Nah.....

(this from the king of typos... )
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Old 04-03-2014, 07:15   #5
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Re: 3HM35 Yanmar stalls under load. What next?

Again a stupid question, but an easy one that costs nothing to check.
Does the prop shaft spin freely in neutral? What does the RPM drop to in idle in gear?
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Old 04-03-2014, 07:15   #6
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Re: 3HM35 Yanmar stalls under load. What next?

Quote:
Originally Posted by MarkJ View Post
This may soubd stupid as you obviously know more about engines than I do, but why don't you increase the idle speed a bit?

Mark
Well, I know a little about the inside of internal combustion engines but don't have much experience working on diesels. I've rebuilt a number of gasoline engines for cars, trucks, motorcycles, airplanes, and have done rebuilds on maybe a dozen four and two strokes. But no diesels. We had two Land Rover diesel Defenders until this year, but never had to touch the engines.

I've got the tech manual for this one. The procedures are well spelled out, and I can keep digging but I'd really like to exhaust (no pun intended) all the obvious external stuff before taking the head off.

I'll be back on the boat this morning and will look into the whole exhaust restriction thing a little more. I don't have the sharply bent mixing elbow that I've seen some Yanmars have. This one should be quick and easy to inspect from the hose end.
If I don't find any restrictions of consequence there, I'll reassemble and bump up the RPM by a hundred. Thanks for the suggestions. I really don't feel like cracking this one open if I don't have to.

Yeah, I know. "quick and easy" are on the all time list of Famous last words
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Old 04-03-2014, 07:24   #7
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Re: 3HM35 Yanmar stalls under load. What next?

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Again a stupid question, but an easy one that costs nothing to check.
Does the prop shaft spin freely in neutral? What does the RPM drop to in idle in gear?
Yep, can turn it by hand in neutral no problem. Will check RPM drop in about an hour.
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Old 04-03-2014, 07:25   #8
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Re: 3HM35 Yanmar stalls under load. What next?

Quote:
Originally Posted by Canibul View Post
Well, I know a little about the inside of internal combustion engines but don't have much experience working on diesels. I've rebuilt a number of gasoline engines for cars, trucks, motorcycles, airplanes, and have done rebuilds on maybe a dozen four and two strokes. But no diesels. We had two Land Rover diesel Defenders until this year, but never had to touch the engines.

I've got the tech manual for this one. The procedures are well spelled out, and I can keep digging but I'd really like to exhaust (no pun intended) all the obvious external stuff before taking the head off.

I'll be back on the boat this morning and will look into the whole exhaust restriction thing a little more. I don't have the sharply bent mixing elbow that I've seen some Yanmars have. This one should be quick and easy to inspect from the hose end.

Yeah, I know. "quick and easy" are on the all time list of Famous last words
There's something else wrong besides low compression... Don't forget the muffler too... Try a fresh jug of fuel plumbed straight to the lift pump?

Oh man... you said it out loud....

PS I have a few of those $15-20 USB endoscopes... I find it them very handy...
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Old 04-03-2014, 07:37   #9
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Re: 3HM35 Yanmar stalls under load. What next?

I asked as I have seen a little bit of line on a shaft do exactly what you are describing, I think even mono-filament line might could.
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Old 04-03-2014, 07:37   #10
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Re: 3HM35 Yanmar stalls under load. What next?

Exhaust restrictions usually almost always show up as restricting full power / RPM, doesn't it?
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Old 04-03-2014, 11:23   #11
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Re: 3HM35 Yanmar stalls under load. What next?

I was at the boat this morning. I removed the mixing elbow and it didn't look all that bad to me. I scraped out this black sooty gunk. Total volume of gunk would probably fill my fist with a mass about the volume of a golfball. However, after I put it back together and warmed it up, I could not get it to stall with the clutch. I shifted back and forth dozens of times. Not a single stall. Knocking on wood here.

It runs at about 900 RPM now when first cold. It's ragged at that frequency, so I bump it up to about 1000 til it smooths out. After warming up it eventually settles out around 800 at idle. I watched the tach as shifting, and while I could easily hear and feel the load of the shaft and prop, the tach needle only moved slightly and then settled out at pretty much the same RPM. So I think that tells me that the governor low speed idle is working fine. If I understand how this works, from reading the tech manual. Governor uses centrifugal force to give it a boost under load at low speeds, and also keep it from running away at high speeds if the prop falls off.

The thing is I have not yet found a single source of failure to explain it. I guess it's possible that the leaky banjo bolt, the filthy air cleaner, and the slightly restricted exhaust could have collectively caused a loss of low rpm power? Diesel pneumonia? It's running well enough now that I see nothing else I need to do to it. I need to look up what the idle RPM should be, warm or cold, and adjust that. I don't think it's good to idle it too fast and then shove it into gear at a higher RPM.
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Old 04-03-2014, 11:34   #12
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Re: 3HM35 Yanmar stalls under load. What next?

Did you try cracking the injector lines one at a time to see if it changes anything? A marginal injector can cause the symptoms you describe.
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Old 04-03-2014, 14:05   #13
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Re: 3HM35 Yanmar stalls under load. What next?

You mean crack them sequentially, and the one that has no effect is the bad one, right?

I haven't done that. I did have all three rebuilt in Jax, so I know the injectors started out good. I also installed two Racor 500 filters so I know the fuel has been clean. About a week ago I took the injectors down to the local diesel shop and they put them each on one of those Yanmar pump injector testers and they were all three good. They fired when they reached whatever pressure it was.

We are down to about our last quarter tank of fuel. We started out with US fuel, but topped up in the Bahamas on the way down. What's left in the tanks is a mixture and it's two years old. It's clean, but it's old. I know diesel has a long shelf life, but I'm wondering if this could be a factor in a tropical climate. Does the good stuff evaporate out of diesel like it does with gasoline? Should I be adding something to the tanks?
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Old 05-03-2014, 08:36   #14
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Re: 3HM35 Yanmar stalls under load. What next?

Quote:
Originally Posted by Canibul View Post
The thing is I have not yet found a single source of failure to explain it. I guess it's possible that the leaky banjo bolt, the filthy air cleaner, and the slightly restricted exhaust could have collectively caused a loss of low rpm power? Diesel pneumonia? It's running well enough now that I see nothing else I need to do to it. I need to look up what the idle RPM should be, warm or cold, and adjust that. I don't think it's good to idle it too fast and then shove it into gear at a higher RPM.
I think it's a combo of everything.... engine hours, all your restricted breathing treatments, and older fuel... One on its own not enough... all together... just enough...

Quote:
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You mean crack them sequentially, and the one that has no effect is the bad one, right? Yes... but listen for "less effect", not NO effect.... you might be able to have somebody see it on the tach too...

We are down to about our last quarter tank of fuel. We started out with US fuel, but topped up in the Bahamas on the way down. What's left in the tanks is a mixture and it's two years old. It's clean, but it's old. I know diesel has a long shelf life, but I'm wondering if this could be a factor in a tropical climate. Does the good stuff evaporate out of diesel like it does with gasoline? Should I be adding something to the tanks?
Quote:
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Continue your exhaust restriction investigation... elbow to hull...

Prop? Fouled?

Restricted or BAD fuel?

Can you bump the idle 100 rpm?
Diesel will last an AMAZINGLY long time stored correctly... But there are numerous stories of 1-2 year old fuel causing a depreciation in performance.... I've heard of additives to increase performance of the fuel, but have no experience here.... Only saving fuel from going bad...
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Old 05-03-2014, 11:13   #15
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Re: 3HM35 Yanmar stalls under load. What next?

I just spoke with the owner of the marina about diesel shelf life here. He cited his own boat, a 30 year old motorsailor with twins. He says they still fire up instantly, no cranking, but immediately, with fuel that's been in the boat for at least 10 years with no additives.

He was telling me about algae, but says it hasn't been a problem. His theory on that is that the boat hasn't moved and so there's no sloshing to wet the sides of the tanks, etc.
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