Black smoke on start of my Hunter 28 (2GM20G Yanmar engine)

[Seb6226$]

Friends
Just got the sailboat recently. Black smoke and high temp signal is on when I start the engine. Coolant level is at max in the tank and mid level in the overflow tank. Seacock is open and no seaweeds at clogging the little basket on the waterline leading to the engine. She is due for an oil change, but I would like to warm up the oil a bit before proceeding but I can’t.
Any idea on what to do to avoid black smoke and high temp? Thanks

 

[garymalmgren]

Hi Seb
I have a few points to clear up before coming to an answer to your questions.

RE Black smoke and high temp signal is on when I start the engine.
Does the black smoke clear up and the high temp alarm go off after a few minutes?

RE: Seacock is open and no seaweeds at clogging the little basket on the waterline leading to the engine.
Is there water exiting the exhaust?
It should come out in pulses of a quart or so each time.

RE: She is due for an oil change, but I would like to warm up the oil a bit before proceeding but I can’t.
You can change the oil anytime after you have sorted out your intitial problems. One thing at a time!


A couple of thoughts.
If you start up with the throttle fully open you will get a big slug of fuel into the engine on start up. This will create black smoke.
Then when you idle back the black smoke should disappear.

There is no way that your engine will be overheated in the first few minutes of start up. The alarm going off would indicate a problem with the temp sensor or wiring, But that is just a guess without further information.

Gary

 

[Seb6226$]

Thanks Gary- Much appreciated

The first time I took her form the marina to my mooring (last week), I was able to cruise and when the high temp light turned on, I turned the engine off to let it cool.. and
turned it on after 10 min. Water was coming out of the exhaust periodically and yes, black smoke was clearing out after a while.

Yesterday, I only tried to turn it on and black smoke was coming out so I didn't want to push the envelope since I was already home on my mooring...

My plan is to change the oil, fuel filters, impeller, air filter to reset the maintenance since I'm not sure oof what has been done and when. Belts seem in good shape.

Any advice? Hopefully not the thermostats or the elbow...!

 

[Tally Ho]

Hi Seb,

I also have a 2GM20F Yanmar in my boat. I also get some black smoke out the exhaust when I first start my engine. As Gary said, when you open the throttle to start the engine (which I do), there is some unburned fuel that gets blown out the exhaust. Mine clears up almost immediately of the engine getting to a high idle. I do pull back on the throttle as soon as I hear the engine “catching” and the rpm’s starting to speed up.

On the alarm, the Yanmar panel does alarm as soon as the key is in the “On” position, and it stops once the engine is running. I always thought that was a low oil pressure alarm…not a high temp alarm. Or maybe just to let you know the engine stopped.

How do you know you have a high-temp alarm? Does the alarm stop once the engine has started? As Gary said, you should see water spurting out of the exhaust. Sounds like you checked for blockage in the intake and strainer. How about the impeller? Have you changed it recently? The water flow out of the exhaust is an important indicator. But like Gary said, the engine isn’t overheated upon starting it.

Greg

 

[Seb6226$]

Thanks Gary
The high temp alarm was starting after 15+min of cruising. I stopped to let the engine cool and cruised again after 10 minutes, but it went on again. Coolant tank is very full. It due for an oil change but I don't think it can be that, can it? 'll change the impeller today and see.
Your comments are very valuable. Thanks

 

[Tally Ho]

A few other thoughts after reading your follow up post…

1) How far did you motor when the engine overheated? And how many RPMs were you pushing? I once had my high temp alarm come while motoring very hard. There was black “soot” in the exhaust water. I believe I was over-propped and I was pushing the engine to the point it could not burn all of the fuel and it overheated. I pulled back on the throttle and the alarm stopped pretty quickly and I motored the rest of the way without incident.

2) When I took delivery of my boat, I failed to check the AF in the heat exchanger. I hit the lake for a long push against waves and a head wind. I don’t know what RPMs I was running, but soon after hitting the lake, the alarm went off. I reduced throttle and limped to the next marina. After the engine cooled off, I opened the cap on the HX and found no liquid in there I filled the heat exchanger and motored home the next day.

I am assuming your 2GM20 is the freshwater version…if not, #2 is not really helpful.

Greg

 

[Seb6226$]

Thanks
I was only going at 1500 rpm approx, but she hadn't been in the water for 6 weeks and had to be transported from one lake to another on a trailer. I do have an HX but havent touched it. What did you put in it? Water or coolant? My engine is cooled by both.

 

[Michael Davis]

Water or coolant?

Mixed like your car. When you change your raw water impeller if it is missing vanes you will likely need to re and re the heat exchanger too.

 

[Art12050]

Clogged mixing elbow?

 

[Claude L.-Auger]

Excellent ideas and suggestions by previous posters !
To clear matters up: you have 2 sensors on the engine that trigger the same alarm:
1) the oil pressure sensor. It will make the alarm buzz when you turn on the key. As soon as the engine has started and run a few seconds, oil pressure has built up and the alarm goes off
2) the high temperature sensor will trigger the alarm only when engine temperature gets higher than normal, i.e. over 165 F or 171 F depending on which thermostat you have.
You say your engine is cooled by both water and antifreeze. To clear matters again, your engine run with a mixture of antifreeze and water in the engine. That mix is itself cooled by the heat exchanger. That works much like a radiator on a car except that it is cooled by raw water being run inside the exchanger. The raw water picked up by the impeller pump runs through a filter (skimmer) and then goes to the exchager then is expelled in the exhaust after being push in the exhaust elbow. The antifreeze itself runs inside the exchanger but outside of the little pipes.
Since you heard the high temp alarm after +/-15 minutes then you could have an issue with:
a) not enough antifreeze in the exchanger
b) blocked water pick-up through-hull or blocked raw water filter (skimmer) before pump
c) defective impeller
d) clogged hoses (if defective impeller, blades could have plugged up the hoses or the exchanger itself)
e) choked up exhaust elbow, preventing proper flow
The alarm could also be triggered by a defective thermostat.

Check all of these things and correct as needed and you should be good to go without hearing that dreadful sound !
Good luck

 

[jssailem]

1. Any idea on what to do to avoid black smoke and high temp?

Yes

• Regularly do all maintenance on your engine.
• Do not start the engine with the fuel control wide open.

That was the simple answer.

There is a bit of stuff packed into your thread. Let’s try to decode what I think I see happening.

Your observations.

1. Black smoke and high temp signal is on when I start the engine.
   • These symptoms are not connected other than you are starting the engine. When you start the engine from it sitting overnight or after a long shut down there is no possibility that the engine is over heating. Something else (possibly electrical) is triggering the “High Temp signal”. Do you have a temp gauge or just an idiot light? Get a cheap IR temp gauge and use it to examine your engine an every time you suspect that it is over heating.
   • Here is good info on Engine Temp issues. Engine Temp Monitoring And Overheating Assessment - Marine How To
2. Coolant level is at max in the tank and mid level in the overflow tank.
   • Good status
3. What did you put in it? Water or coolant? My engine is cooled by both.
   • These engines thrive on a 50/50 water coolant mixture. You don’t have it on the boat you can use fresh water (not seawater). Then when you do your maintenance (soon) replace with a 50/50 mix.
   • Your engine block is directly cooled by the coolant/water mix you put into the Coolant tank.
   • You suck in Raw water from outside the boat pass it through the Heat Exchanger (HX) and out the exhaust. This Raw water is transporting the engine heat off the boat.
4. Seacock is open and no seaweeds at clogging the little basket on the waterline leading to the engine.
   • Good Observation and maintenance
5. She is due for an oil change, but I would like to warm up the oil a bit before proceeding but I can’t.
   • Nice but not a requirement.
6. I do have an HX but haven't touched it.
   • TOUCH IT. CLEAN IT. You need to, at least once a year, inspect the HX. Think about it as the AC of your engine. You drive you engine to high temps and the HX sucks that Heat out of your boat using RAW water to keep the engine running cool.
   • You ignore your HX and it will be like putting your engine on the asphalt in the middle of a 125º heat wave in the Arizona sunshine.

Your engine needs to run at well above 1500 RPM’s. Run it up under load to 3000 RPM’s. If you see black smoke then you have a carbon in the engine. It has not been run up to temp and carbon from unburnt fuel is formed in the cylinders. It is possible that SeaFoam additive might help clean it up. Hard to tell. You may find that giving you engine a chance to run at 3000 RPM will help to blow out the crap that is in the engine.

I would look again at your coolant system. (Sometimes call the “fresh water” system in the manual). Check your engine water pump for any weeping of coolant, The Impeller on your raw water pump, The hoses, and The Heat Exchanger to affirm that all are allowing fluids to flow without any obstruction. I would check yout thermostat. Is the correct one installed? Is it working properly?

I would install a temp gauge so you can know what the operating temp is for you engine. Should be in a range of 140 and 170. I would use the IR sensor to check the engine when ever you sense that the engine may be running hot.

 

[garymalmgren]

Hi Seb
RE: My plan is to change the oil, fuel filters, impeller, air filter to reset the maintenance since I'm not sure oof what has been done and when. Belts seem in good shape.

Most of those things will not effect your cooling problem.
Stay on course!
There is no need to change out the impeller IF THERE IS COOLING WATER DISCHARGING FROM THE EXHAUST.
Is there water exiting the exhaust?
It should come out in pulses of a quart or so each time.


Gary

 

[Seb6226$]

Folks, i started the engine, there was black smoke and it disappeared after less than a minute. I let it run for 5 min and turned it off. No high temp signal. I took this opportunity to change the oil and it went like a charm. After I started the engine and after 5 min, I saw white smoke…. Water is coming out of the exhaust so the impeller use be great. Now… why white smoke!!!!!

 

[Tally Ho]

Folks, i started the engine, there was black smoke and it disappeared after less than a minute. I let it run for 5 min and turned it off. No high temp signal. I took this opportunity to change the oil and it went like a charm. After I started the engine and after 5 min, I saw white smoke…. Water is coming out of the exhaust so the impeller use be great. Now… why white smoke!!!!!

Glad you got it going and got the oil changed.

White smoke is usually a sign of moisture in the system….not sure what the source would be. But before you get too worked up, I would run the motor for a bit…15 minutes or more, and get it up to temperature (so motoring around at 2,000-3,000 rpm’s).

Then check for smoke.

Of course if any other alarms go off, or you notice any major smoking issue, stop and reassess.


Greg

 

[jssailem]

If I am concerned about an engine to the point of taking it out on the water (I might get stuck out on the water). I tie the boat up in the slip and I run it in gear until the engine gets up to temperature. No risk no fuss.

 

[garymalmgren]

RE: After I started the engine and after 5 min, I saw white smoke…. Water is coming out of the exhaust so the impeller use be great. Now… why white smoke!!!!!

How long did you see white smoke for?
Photos or video of the smoke/ steam would help us nail it down.

It could be a one off situation. Don't panic!

gary