Yanmar 3GM30F Problems (HELP!)

Hello all,

I am having an issue with my Yanmar 3GM30F that hopefully one of you can help with.

I went to my boat on Friday and fired up the engine in preparation of a day on the water yesterday. The engine ran great and I ran it long enough to warm it up then shut it down. I went back to the slip with my family yesterday and the engine acted completely differently.

First off, it was hard to get started. Once it fired up, there was a popping noise coming from the air intake every time the number one cylinder fired (almost like a backfire?). I opened and closed each of the decompression levers one at a time and when I opened the number one cylindar, the popping stopped. Do you think I have an intake valve on the number one cylindar sticking. Are you concerned with a slight film on the surface of the antifreeze when I open the cover? Also, when I started it yesterday, the plastic antifreeze reservoir overflowed hard enough to knock the lid off.

That started my mind in the direction of a head gasket allowing compression into the water jacket and compressing the fluid in the reservoir, thus blowing the lid off the reservoir. Would this cause a popping noise at the air intake? Am I thinking too much into this?

I bought the boat used so I don't know the history of the engine but it has ran like a champ since I got it and did fine during a 200 mile on-engine run from Miami.

Could it be something else? What is the fix?

Also, what grade/brand of motor oil do you suggest? I am not sure what API Service "C" is. I used what the manual suggested (30 weight).

Any advise would be appreciated, I want to go sailing.




Ray Tarr
Patrick AFB, Fl
1963 Allied Seawind, Crackertail
Hull # 25

 

Valves don't normally stick on their own unless they are somehow bent. My guess would be a bad head gasket or a cracked head. Check for water in the oil, it is a good indicator of a bad head gasekt. A compression test is also a good troubleshooting aid. Did you confirm that you had cooling water coming out the exhaust when you warmed it up on Friday? Overheat is a very common cause of head/gasket problems.

 

You guessed it.

The problem is most likely a blown head gasket. This scenario suits all your symptoms.