Universal M 3 20

[PeteT]

Its crazy. I start the engine and that sometimes takes a few times to get it going from a cold start. It runs fine at the dock for ever and then when under way it will sometimes just stop and it's hard to start again. Then after a while it fires up runs perfect, idles at about 800 R's and then dies.... It could be running for 30 minutes perfect and still. I have checked the tank and she is spotless, no water in the Racor... not sure where to go from here and getting a mechanic is like pulling teeth. Oh while I am thining about it. This is a 1980 Cat 30. so the engine is mounted underneath the galley counter. I was wondering if anyone has pulled off the counter to get easier access to the engine. She need a bit of a wash too . Any ideas?

 

[JoeWhite]

Sounds like fuel starvation. Replace both fuel filters. Then clear the fuel hose from tank to primary filter. Then make sure the primary filter is always full of fuel. Also take a 2 gallon diesel jug with fuel in it and with a fuel hose connect to the primary fuel filter run the engine.
Check the fuel tank vent if it is blocked. When the engine stops remove the fuel fill cap and see if the engine will run.
This exact problem happened to me.

 

[Davidasailor26]

In the adage that diesel engines need fuel, air, and compression your symptoms seem to make it unlikely that the air or compression are the problems - those aren't likely to change after a random amount of run time. Maybe a small leak in a fuel line letting it pull air in intermittently, when a fuel hose vibrates and moves the wrong way? I like @JoeWhite 's fuel vent possibility too.

 

[Stu Jackson]

In ADDITION to this fine advice, there is this:

Fuel Starvation and The Obscure Check Ball Valve
Fuel Starvation and The Obscure Check Ball Valve
and
Fuel Starvation and The Obscure Ball Check Valve

Sounds like fuel starvation. Replace both fuel filters. Then clear the fuel hose from tank to primary filter. Then make sure the primary filter is always full of fuel. Also take a 2 gallon diesel jug with fuel in it and with a fuel hose connect to the primary fuel filter run the engine.
Check the fuel tank vent if it is blocked. When the engine stops remove the fuel fill cap and see if the engine will run.
This exact problem happened to me.

 

[jssailem]

Agree... Fuel would be the suspect high on my list to chase down.

You say the boat was built in 1980. This would suggest the fuel lines were installed 44 years ago. If they are original it might be time to replace them. This would serve to assure there is nothing in the lines that could be causing an issue. It would also address the possibility of air leaks (post #3).

The easy places to check include all of the connections for contamination, the filters, the inlet in the tank (is there a strainer on the inlet hose at the bottom of your fuel tank?), any check valves (post #4 above), fuel lines from tank to engine and the lines on the engine and of course the vent line (as has been noted post #2).

It is a great way to spend a weekend.
To borrow a movie quote...
"I love the smell of DIESEL in the morning..."