Hot, smoking yanmar

[dave_and_dd]

Well not "smokin hot" in the good sense...Ok, so here’s the story. We go out a couple weeks ago and while motoring I start seeing dark smoke coming out and the temp gauge is climbing. Well, we took it down to idle and let it run a while (it cooled) and when we came back in, we only used the motor for the last couple minutes to dock.

Now I’ve been reading all the engine stories for the 3 years we’ve owned this boat (2007 Catalina 309, 3YM20 with about 750 hrs). so I knew to expect a mixing elbow problem. I bragged to my wife – I know exactly what’s the problem. Proceeded to take everything apart over the next couple days and get the mixing elbow apart. Sure enough there’s lots of junk in there.

Did the following:

• replaced mixing elbow
• exhaust elbow
• exhaust tubing to muffler
• hard-wall tubing from heat exchanger to vacuum breaker and back to mixing elbow
• rodded out heat exchanger
• replaced impeller
• replaced thermostat
• replaced input line to raw water pump which had a kink or bit of a collapse in hose

So now 1) there’s got to be better raw water flow and 2) engine has to ‘breathe’ better with the new mixing elbow.

Took the boat out last weekend, same issue. At cruise rpms, things are ok, but if I push the engine, pretty quickly temps start rising and dark smoke starts coming out. Confirmed there’s plenty of water coming out the exhaust.

(See pics below of old mixing elbow and of engine with new one installed)

A couple more symptoms to note:

1. This started suddenly. I try to push the engine to near full rpm for a bit of our transit out the channel every time we go out. I don’t just baby the engine.
2. This is not accompanied by any loss of power/rpms. The engine is running well and the boat is moving along. I don’t trust the tach…but it’s saying I’m going like 3800rpms.

My next steps – check to make sure no obstruction in the air filter? Not likely but could be something simple like that. Also, need to get a portable tach to tell for sure the rpms.

Other thoughts - next things to start looking at? Any insight would be appreciated,

Dave in Tampa

 

[jviss]

Dark smoke and overheating sound to me like the engine is overloaded. Is the bottom clean? Prop clean?

 

[Gunni]

Why were you running that engine at an observed 3,800 RPM.

 

[Roland5048]

. This is not accompanied by any loss of power/rpms. The engine is running well and the boat is moving along. I don’t trust the tach…but it’s saying I’m going like 3800rpms.

I've got the same engine with just under 700 hours. WOT is rated at 3600 rpm. When my hull, prop get fouled the max rpms fall significantly but no smoke. That you can achieve 3800 rpms suggest an under pitched prop. OK, that doesn't directly address your concern, but might give you some baseline.

My next steps – check to make sure no obstruction in the air filter? Not likely but could be something simple like that.

Don't rule that out. At about 400 hours my filter was completely disintegrated. It's just a foam cone over a metal mesh cone. Could be some bits stuck somewhere.

Also, need to get a portable tach to tell for sure the rpms.

Yes, that and a laser heat thermometer. My panel only has idiot lights so I keep one on board.

At cruise rpms, things are ok, but if I push the engine, pretty quickly temps start rising and dark smoke starts coming out. Confirmed there’s plenty of water coming out the exhaust.

If you are really pushing 3800 rpms I would think you are really overloading those 21 horses. Dark, black smoke usually indicates unburned fuel. If you are lucky your problem may only be the high rpms caused by an under pitched prop or the throttle cable needs adjusting.
Just my off the cuff thoughts. Let us know what you find. Good luck.

 

[weinie]

according to the 3ym20 service manual, the no-load maximum speed is 3890+/- 25.
I imagine with a load on it, it might be a couple hundred rpms lower.

 

[Charles Erwin]

Usual suspects in sudden overheat onset:

Seawater intake/strainer blockage or restriction. Seawater pump impeller. Coolant thermostat. Coolant circuit restriction or air (especially if there is a water heater.) Coolant pump.

Charles

 

[Roland5048]

according to the 3ym20 service manual, the no-load maximum speed is 3890+/- 25.

That's true. In neutral, rpm will go to 3800+. Loaded up max 3600. When my engine was put in, loaded rpm would go to 3800. Had the prop repitched so max under load is 3600. Where it should be. I normally run about 3000 rpm which is 83% of WOT. Run it up for a minute to WOT (3600) when it's warmed than bring it back to 3000. Before shutting down, I run to WOT in neutral for a couple of seconds to push any carbon out because I have about a 30 minute ride out and in in a no wake zone that only lets me get to about 2400 rpm.

 

[Davidasailor26]

It sounds like the black smoke came first followed by the temperature increase? If so the root cause may not be a cooling issue but some kind of overload. What does your tach read at WOT, and do you know if it's the OEM prop or could've been changed along the way?

 

[kloudie1]

Small air leak in sea water strainer? Water pump drive belt tension OK?

 

[dave_and_dd]

ok, let me address a couple items.
1. the tach is crazy. sometimes at moderate cruise it suddenly says i'm 'pegged' at 4k rpms. with it un-reliable, I'll need to get an optical tach and verify actual revs. having said that, i'm guessing it was reading a bit high when last out...but will verify.
2. bottom / prop growth. It's been hot water in Tampa. Growth is crazy. So, it might have a bit. I'm going to try to clean it up over the weekend and try. And will inspect prop.
3. Actually not the OEM prop. I know it's the same pitch/diameter (not that that tells all). But did replace it 2 years ago due to a different problem.
4. Water is flowing well for the raw water system. That's all pumping nicely.
5. Air in coolant? well, I do have a hot water heater. this problem started months after coolant change. was not exhibiting any loss of coolant, but that was over the winter and spring (cooler weather). now to replace the thermostat I did also change the coolant. but once filling it up, I warmed it up and then bubbles 'belched' and refilled a couple times. I think there isn't air lock in the line to the HW heater, but not sure how to be sure...

Dave

 

[Stu Jackson]

the tach is crazy. sometimes at moderate cruise it suddenly says i'm 'pegged' at 4k rpms. with it un-reliable

Have you checked for a loose connector? At both ends?

I think there isn't air lock in the line to the HW heater, but not sure how to be sure...

If there was air in that coolant circuit, you would know right away: runaway overheat almost immediately. It's one of those either it is or it isn't. No partials here.

 

[Charles Erwin]

Dave - How about the intake side of things? Did you suck up a plastic bag, the odd crustation, weed, sticklefish? Do you have an external slotted cover over the intake sea cock? Growth there will restrict the intake to the seawater pump but you won't see it unless you dive and clean.

Edit: You say outflow of seawater is good. You should be doing about 4 gpm at idle (900 rpm) and about 9 at 2500 rpm. If so then your problem is on the coolant side of things but measure seawater outflow - even if crudely .

 

[weinie]

I'm guessing the coolant is not circulating. Is your water heater producing hot water after you run the engine for a while?

 

[Benny17441]

It is never a good practice to start doing work or replacing parts Willy-Nilly. Diagnosis is a process of elimination and we start with the least expensive and the least labor intensive possibilities. We study the symptoms and concentrate on those possibilities that match the symptoms. For example dark exhaust smoke and rising temperature are symptoms of a fouled prop. I would have started by inspecting and even cleaning the prop and boat's bottom. As it could be a compound problem I would check the coolant level and the coolant flow. Disconnect a couple of hoses one at a time and pump some coolant into a bottle observing the flow stream. If you find a point of low flow then there is an obstruction in the component upstream. Test the thermostat so that it is opening and closing adequately. On the raw water side I would just have checked the exhaust water flow to determine if the impeller or mixing elbow needed immediate attention. We have to resist the urge of looking for solutions before we fully define the problem. .

 

[dave_and_dd]

Stu - yes, i've checked the tach connections. what seems to be the problem is this (recommendation from the manufacturer) - the dial on the back that you set for the type (from memory don't remember what was it - number of poles or something)...they suggest that it may get dirty in the marine air and to turn it back and forth a couple times. when i've opened the panel and done that, it has settled down for a couple months. even so...unless you all have calibrated your tachs - you will generally find them not to be too accurate. Use an optical one.
and thanks for confirming an air lock would be immediate - that's what I was thinking...(and the hot water wouldn't get hot).

Benny - The reason I opened up and went for the mixing elbow - I've had the boat 3 years and who knows when before that it was cleaned or replaced. Additionally, it was slightly leaking. It turned out to be pretty clogged...so, it's time I did that anyway. The hoses that I replaced were all a bit cracked looking and needed it. The impeller...well it was about time to do (annual). And the hose feeding the raw pump was developing a flat spot in a bend and had to be restricting flow at least a bit....needed to do that right.

Weinie - the hot water is getting hot - yes.

Charles - when you say intake side of things...if you mean air intake, that's my next place to look. Raw water intake is flowing well.

Thanks folks...will be working on it over the weekend and see what else I find.
Dave

 

[Charles Erwin]

Dave

No - not air intake. Air intake restriction might make things rich (unlikely in a diesel motor by the way) thus smoke but this will not lead to a dramatic overheat.

Intake = seawater intake/output. You say it is flowing well. How much at idle - how much at 2500? Easy and cheap - as Benny correctly observes - just put a 5 gallon bucket under the exhaust, time it for 30 sec, end of exercise. If these volumes are as the pump manufacturer says - see above - your overheat problem is in the coolant circuit.

None of us are there, we cannot observe, so we have to rely on what you tell us - thus it would help if you could quantify. If no data then expect no diagnosis.

Charles

 

[BrianRobin]

Yanmars must have a short stroke to wind that high, if you did that to a Perkins you'd be picking crank pieces out of the hull! My redline is 2400, never had mine past 2200 though.

 

[weinie]

How bad is the smoke?
Is it really nasty clouds of smoke or just black soot on the transom?

 

[dave_and_dd]

As Emily Litella would say….”nevermind…”
A number of youz guyz were pointing in the right direction - load. So with a clean bottom and clean prop this weekend – I couldn’t get the issue to happen. “Ran like a top” and the gauge didn’t start to climb and no smoke when throttled up.

I checked the rpms with an optical tach as I’ve seen suggested by MainSail (some stats below as an FYI). As I was saying the built-in tach was definitely off (but I knew it would be as it has changed over time even when we know the approx. speed by feel and sound – but needed quantifiable stats). I did not measure the water output as that seemed like it would be a difficult task since the exhaust exit is pretty much right at the water-line and there was a good amount of water flowing. Holding a 5gal bucket under it would be tough.

Here’s the other observed measured stats with optical tach and IR thermometer:

• <edit> the stats i entered didn't format well....so i'm putting them in a separate post as an image

Dave in Tampa

 

[dave_and_dd]

Here are the stats in an image as comparisons...