Coolant issues for Yanmar 3GM30F

[bgallinger]

I ran my Yanmar for 3 hours at 2500 RPM then stopped at a marina. After 4 hours went by, I looked in the heat exchanger to check the amount of coolant and discovered that a lot had flowed into and filled most of the reservoir. During the 3 hour run I checked the temp of the coolant several times and it was steady at 165 F. I read somewhere that the coolant would flow back into the heat exchanger when the engine cooled down.
Is the engine running too hot?
Would the coolant have flowed back into the heat exchanger on its own after cooling down?
I shouldn't have to remove the coolant from the reservoir and place it in the heat exchanger every time I run the engine!
This coolant issue is making me crazy!

[tkeithlu]

Your engine ran at 165 degrees, which is your thermostat setting. That's just as it should.

If you openned the cap to the coolant, you lost the vacuum that would draw the overflow back into the system. The excess coolant isn't necessary for cooling the engine - most of us don't have overflow tanks but keep the coolant level below what will vent, or we get coolant sprayed all over the engine.

[Bill O]

Originally Posted by bgallinger

I ran my Yanmar for 3 hours at 2500 RPM then stopped at a marina. After 4 hours went by, I looked in the heat exchanger to check the amount of coolant and discovered that a lot had flowed into and filled most of the reservoir. During the 3 hour run I checked the temp of the coolant several times and it was steady at 165 F. I read somewhere that the coolant would flow back into the heat exchanger when the engine cooled down.
Is the engine running too hot?
Would the coolant have flowed back into the heat exchanger on its own after cooling down?
I shouldn't have to remove the coolant from the reservoir and place it in the heat exchanger every time I run the engine!
This coolant issue is making me crazy!

I can't remember if you changed you cap or just reused the old one? You are correct the coolant should go to the motor from the resivoir when cooled down.

I'm thinking somewhere in the system you are losing vacuum (when cooling) to return the reservoir fluid back to the exchanger/header.

Main suspects would be the cap, but also would tighten any hose clamps and check hose ends for minor cracks.

[bgallinger]

I repaired the cap so it seals properly, so I no longer have coolant leaking out. Perhaps I need to wait longer to let the engine cool down completely.

[Compass790]

Originally Posted by bgallinger

I repaired the cap so it seals properly, so I no longer have coolant leaking out. Perhaps I need to wait longer to let the engine cool down completely.

Yes you do.

[George DuBose]

After a long day's run of my Yanmar 3GM30F, I always let the engine idle for 5-10 minutes before shutting down.

I also pump the throttle 2-3 times and then pull the engine stop quickly, this seems to help on the next starting.