Yanmar 2-cylinder Overheating Problem

[funsail]

I have a 1986 Hunter 31 with about 1000 hours on the 2-cylinder 18hp Yanmar engine, which is fresh water cooled. I just launched it Friday, 10 May, and was proceeding to take it to my slip about 6 miles away. After about 15 minutes away from the Marina, I saw steam coming from the exhaust, and then the engine stopped. The engine overheating alarm didn't go off? I anchored and got a tow back to the Marina. When I first looked at the engine, I noted that the coolant reservoir had popped its top and had overflowed a lot of coolant. After the engine cooled, I opened the coolant cap and could not see any coolant. I checked the raw water impeller which was fine. Since the coolant was pushed back through the reservoir, I suspect that either the head gasket or a warped head is the cause of my problem. The coolant did have some very fine black particles in it, for which I have no explanation.
To check my theory I though of taking out the thermostat and running the engine with the coolant cap off. If I see bubbles coming up my theory is correct.
I WOULD APPRECIATE ANY INPUTS OR THOUGHTS ON THIS PROBLEM.

 

[Scott]

do big deal

I think you have either/or/and a bad cap or thermostate. Can't think of anything else that would cause your problem.
As far as the black sediment, it's prabably a result of overpresurizing and high temp which may have caused off scaling of rust. Don't believe it's anything major.:dance:

 

[sailaway78]

More info

More info needed. I would fill the reservoir, and start it up. See what happens. If you get bubbles in the reservoir, you are probably right about the head gasket being blown. Did you smell it when it quit. If it was hot enough to cause it to blow a head gasket, I would think you would smell hot oil or something. Get a infra red thermometer, crank it up and while watching the temp, see what is happening.

 

[Bill Roosa]

did you confirm that raw water is flowing?

 

[Chris Patterson]

did you confirm that raw water is flowing?

Mmhmm. Steam and no water?

And, I would for sure change a thermostat and try it before I snatched the head off. If it comes to that though, the head is a fairly simple matter though.

And yes laser thermometer. Seek Grasshopper.

 

[Bill Roosa]

well if no water is flowing in the raw water system........
You can get steam as the residual water in the muffler boils off.
So again, did you confirm that raw water is flowing?

 

[Bill Roosa]

steam coing out with the exhause can only happen in one cercamstance, little or know raw water flow.
If the thermostat stuck closed and the fresh hot water was prevented from reaching the heat exchanger then the raw water does not get hot and simply exits with the exhaust as water. To get steam in the exhaust you either have to have little or no raw water flow or the head gasket blows and the engine anti enters the exhaust making large clouds of steam like stuff. But it smells greatly of antifreeze. Most folks would put that smell in the post. Since you did not I assume that the steam in the exhaust was simple steam......therefore

you need to check the raw water flow FIRST

 

[woodster]

has anyone asked if the seacock to the raw water pump was full open or if it is some what clogged by maybe dirt dobbers.......

regards

woody

 

[teebutch]

Ck the heat exchanger I had one that was full of barnacles that was causing my engine to over heat. I took it off and cleaned it with muratic acid. Motor cooled great after that.

Butch

 

[Benny17441]

A visual inspection of the raw water impeller in some cases might not be enough. Make sure raw water is flowing out the exahust port. If the impeller vanes have become separated from the bushing water will not flow through the exchanger and the engine temperature will continue to rise.

 

[RichH]

If you have 'black particles' in the FW cooling circuit either get a mechanic who does 'black light' analysis of cooling systems, or obtain the blacklight + dye yourself. The dye (tablets) is put into the cooling water, water circulated to fully dissolve the 'tablet', and then 'black light' is shown into the coolant reservoir --- if the black light makes the water 'fluoresce' there is 99% probability of a blown head gasket, cracked block, etc.. and the combustion gases are entering the cooling water. The 'dye' absorbs carbon monoxide from the cooling water, and the black light will make the CO laden dye to fluoresce. You can obtain such 'dye' and the black light apparatus from most 'specialty' auto supply shops, especially those that cater to mechanics and 'hot rodders'. ;-)