Yanmar 2gmf over heating after 30 minutes

[Mark Nooney]

Hi all,
I have a issue with overheating after running for 30 minutes to 45 minutes.
Here are the steps I have taken so far.

1. Changed impeller and made sure the v belt was tight. (twice)
2. Dove the boat to inspect the through hull and ran a screw driver around
the inside of the pipe. Nothing was there to impede the raw water and
the shaft and prop looked good.
3. Changed the thermostat.
4. Opened and brush cleaned the heat exchanger tubes - they were not
bad when I opened the cover but continued to brush them out.
5. Confirmed the cooling circuit with a laser thermometer while I
ran the engine with no load through all RPM ranges for 50 minutes and
did not overheat.

We have been lucky enough to have had wind and be able to get back to
our home port. After step 3 -5 I thought I had it licked. This past weekend
after 30 minutes of engine time the alarm sounded.
Since we had to get sails up I couldn't measure the temperature of the
engine for about hour after the alarm. I did have steam trailing the boat.
I observed on the trip back steam in the following way.
I started the engine for docking the first 5 minutes of running no steam. Then the steam emissions increase over time.
I only had the engine on for 4/10ths of an hour and no alarm. I think if I need that last 1/10th I would had an alarm.

I read about the filler cap being bad and it solved an overheating issue
when a new cap was installed.
How does the pressure cap keep the coolant temperature in check?

The next step is pulling off the raw water hose after the pump and checking
the amount of flow at 1000 rpm - and 2000 rpm and getting a new cap.

One other note my prop is CDI 14x11 which was switched out before the
season from a bent 15x12.

Any thoughts or advice would be welcome.
Thanks
Mark

 

[Dan Hill]

I would investigate the mixer elbow at this point. Good luck with your search!

 

[nolasafari]

I would also say mixer with restricted flow, the small elbow will carbon/coke up. How much water are you getting out of the exhaust? The restricted flow will not cool down the exhasust gases then you get steam.

If the cap leaks the pressure will not build up and the water will boil hence steam(This Steam would come from the engine coolant cap or overflow bottle not the exhaust). Higher pressure can store more thermal energy. A bad cap can leak or relieve the pressure below the designated pressure . Bottom line is replace the cap if in doubt, they are cheap.

In a past life I operated a 1200 lb steam plant on a ship, it was like controlling a Dragon.

 

[Ralph Johnstone]

They can be a little problematic when they get like this .......................

 

[cjfj]

While I'd agree that the mixing elbow might be your problem, one thing I don't see listed is the raw water strainer. should be between the intake and the pump. It woud be much easier to check than removing the elbow.

Jim

 

[Nom De Guerre]

While I'd agree that the mixing elbow might be your problem, one thing I don't see listed is the raw water strainer. should be between the intake and the pump. It woud be much easier to check than removing the elbow.

Jim

True, and if the strainer lid gasket is suspect or the lid isn't snugged down it could be sucking air, reducing water flow.

 

[nolasafari]

True, and if the strainer lid gasket is suspect or the lid isn't snugged down it could be sucking air, reducing water flow.

Or clogged.

 

[Nom De Guerre]

Or clogged.

I'm sure that's what Jim was alluding to... :-D

 

[nolasafari]

I'm sure that's what Jim was alluding to... :-D

Thank you.

 

[Mark Nooney]

Sorry I didn't give all the facts.
Yes there is a raw water strainer.
The Mixing Elbow was replaced at the beginning of the season.
I will have to check the seal on the
impellor cover, hose clamps on the system, and the strainer cover.

I'll keep you informed.
MN

 

[Jim L]

Remember the old. PV=RT on your cap. I was surprised what all the Mixing elbow can influence on the motor's workings.

 

[Parrott]

I had same issues with my 2GM on my Hunter 31, for weeks, found the diaphragm siphon tube line clogged up. Make sure it clear.

 

[Parrott]

Or when it does overheat, just remove the hose on the intake valve in the off position, then open the valve real quick and you should get a real good water flow thru the valve.

 

[Mark Nooney]

I had same issues with my 2GM on my Hunter 31, for weeks, found the diaphragm siphon tube line clogged up. Make sure it clear.

Where is the diaphragm siphon tube?

 

[Charles Erwin]

Mr. Nooney

Based on what you report I would:

Take the cap off the heat exchanger. Run the motor so it gets to operation temperature (thermostat needs to open so motor needs to be at or above thermostat open temperature.)

Look into the heat exchanger (cap is off) - use a mirror if necessary. Do you see the coolant circulating?

If no coolant movement then the coolant pump is not circulating the coolant through the motor and exchanger. Hence, coolant circulation pump failure - not raw water pump.

Charles

 

[Scott]

Did you check

to make sure the belt isn't worn too much and needs to be replaced? Had a similar problem. After exhausting all possibilities and deciding to get a mechanic, I just happened to look down at the engine and noticed the belt was riding a little "low" in the pulley. Replaced belt - problem solved (KISS!):dance:

Although a belt is tight, if it's worn and slick, it will slip under load.

 

[markwbird]

I have a 3gmF and I went through a very similar scenario just last month. Rebuilt the sea water pump, cleaned the heat exchanger, checked fresh water system. It still overheated after about 30 min. Turned out to be a clogged mixer elbow. VERY IMPORTANT, if you flush the system with a hose make sure the engine is running otherwise it will backflow through the exhaust manifold and fill the engine with water. It's a long day of getting the water out of the engine after that.

 

[RichH]

Could be as simple as the exhaust manifold beginning to fail .... slabs of rust in the 'bottom' of the water side of the exhaust manifold becoming 'agitated' (moved off the bottom by the water flow) and partly blocking the flow at the exit of the manifold. Usually when this happens and you stop the engine and let it cool, the 'slabs' fall back to the bottom of the manifold, there to remain until 'next time'.

Your engine should be delivering cooling water out the exhaust at about 3 gallons per minute when the engine is @ 2000 rpm. So, first verify the flow with a bucket and stopwatch when the engine is cold, and then again when you note the 'overheat' condition. Also, note the outlet temperature of the water in both cases. Any restriction in the raw cooling circuit will show up (when at the reference 2000 rpm) ... with a bucket and stopwatch. If no flow restriction (worn pump casing, broken vanes in the piping, bad T'stat, collapsed (internal) hosing, etc. etc.) then look at the condition of fouling in the Heat Exchanger, restricted injection elbow. Such problems are usually: not enough cooling water or inlet cooling water too hot, lugging engine (over-propped or too tight stuffing box, failing exhaust manifold), blocked injection elbow.

It will also benefit you to 'thermally profile' the engine with your IR indirect read instrument, marking down those temperatures of the hosing/piping/casings under normal operating conditions (cruising speed and moderate load, etc.) and then when you perceive that there is a 'problem', compare those temperatures vs. normal operation, including a separate thermal profile of ALL the connections in/out to the heat exchanger .... such a thermal assay of the Hx at constant flow is noted in temperature *differences* between the 4 connections, of course at that reference engine rpm at 2000 rpm when the engine is *under load*, not 'idling' with NO load. A simple 8-1/2" X 10" printed photo with the temps. added by hand/pen will suffice.

 

[Mark Nooney]

Lessons Learned

OK here is the scoop -
I connected a hose to the push side of the raw water pump and ran the
engine for 1 minute. I measured less than a gallon of water. I should of
had 4 gallons/min at 1000 rpm.

Open the raw water filter and nothing was coming from the through hull hose. So took off the hose to the through hull and got a dribble of water.

Now to the wire coat hanger - ran that down and got a 4" spout of water.
After I got the little pieces of wood cleared I connected the through hull
hose, I performed the same test - 4 gallons / min as expected!

Lesson learned - KISS - look at the most obvious first before messing with the rest of the system.

The value in all this is that I completely know the cooling system for fresh and raw water.

Thanks for all the input.
MN

 

[cjfj]

OK here is the scoop -
I connected a hose to the push side of the raw water pump and ran the
engine for 1 minute. I measured less than a gallon of water. I should of
had 4 gallons/min at 1000 rpm.

Open the raw water filter and nothing was coming from the through hull hose. So took off the hose to the through hull and got a dribble of water.

Now to the wire coat hanger - ran that down and got a 4" spout of water.
After I got the little pieces of wood cleared I connected the through hull
hose, I performed the same test - 4 gallons / min as expected!

Lesson learned - KISS - look at the most obvious first before messing with the rest of the system.

The value in all this is that I completely know the cooling system for fresh and raw water.

Thanks for all the input.
MN

:dance: