Coolant leaking from fill cap on heat exchanger

[bgallinger]

I am running a 3GM30F Yanmar engine on my Hunter 340. I have had some issues with coolant leaking out under the fill cap ever since I re-filled the heat exchanger with anti-freeze (I installed a new hot water tank). I think initially I overfilled the heat exchanger. By removing the fill cap, I can look inside the heat exchanger now and I do not see any coolant, but it is still leaking out from under the fill cap when I run the engine. The coolant does not fill the reservoir.
Engine temps are 180 F, cooling water temp into exhaust elbow is 103 F, coolant temp is 165 F

Any ideas?

[pjShap]

I had a coolant cap leak like that and replaced the cap. Not cheap from Yanmar. That was not the problem. The tabs on the filler neck were bent and not holding the cap on properly. Adjusting those tabs eliminated the leak.

[Calif.Ted]

Mine is VERY particular about the cap, when I bought my boat it had an aftermarket cap and leaked as you describe. Replaced with old cap found in nav desk and no leak, tried various caps with same result. The size of the rubber gasket inside the cap seems to be the key. All but the Yanmar cap had a slightly smaller outside diameter of the gasket.

[tkeithlu]

The coolant cap is a pressure release valve. By sealing with some spring pressure on the gasket they pressurize the coolant system, thereby raising the boiling point of the coolant. You apper to have been boiling coolant out the cap. The gasket seal and the spring load are important, and vary from cap to cap. An issue like bent edges on the latching bayonet mount on the heat exhanger can mess up the entire system.

So, check for damage around the rim, see that the gasket is not brittle or cracked, see that the cap seats cleanly and completely. The spring should compress as you turn the cap into place. If you try for a generic cap, thus to avoid highway robbery from Yanmar, take the cap with you to the auto parts store. Be sure the new gasket will cover the area needed. You'll have to guess or experiment a little with the spring pressure needed, but should be able to solve the problem.

[deltaten]

You said that you added a water heater, right?
Perhaps it is that as you added volume, you did not take into consideration the additional expansion of the fluid. Mebbe che k pressure at operating temps? Geting a bigger puke can and properly regulated cap could do it

[Deep Blue Water]

Make sure you use a premium name brand coolant filler cap; the 2nd thing I'd check is that the cooling system isn't being pressurized by exhaust gases leaking into the cooling jacket.

[zstine]

If it is leaking from the brazed joint between the filler neck and the mounting plate/heat exchanger, You may be able to solder the connection to stop the leak. It will have to be clean and dry. I was able to fix my Nanni coolant fill neck this way (it took a few attempts). The Nanni had the filler neck brazed to a plate bolted to the exchanger. I removed the assembly and soldered off the engine. In retrospect, a radiator shop would have been able to fix it properly with brazing it... But I was in a remote location. So if you can remove it, I'd take it to an auto repair shop.... Use a torch to solder and expect paint damage requiring touch up.

If the cap is leaking, then you have coolant getting past the spring loaded seal that should drain off into a tube and overflow bottle. If you don't have a tube and overflow bottle, add one! Check the seal surfaces are clean and the rubber is good. A new replacement cap is cheap and easy fix.

[EmeraldCoastSailor]

I have a 2008 3YM30 and had a nagging coolant leak for quite some time. Just a tiny amount for the most part. I replaced caps a few times; turns out there are generic caps and authentic (and expensive) caps. I then thought it was leaking from the connection to heat exchanger so I put a layer of JB Weld around the filler neck. Still leaked. Finally noticed it was the filler neck that had a tiny crack (see pic attached). I tried to patch it with JB Weld and it worked for a while. I think another crack formed. I ended up removing heat exchanger and replacing the filler neck and copper ring that applies pressure inside filler neck where it meets the HE. Wasn't all that hard once I found the right tool to press the copper ring into place; a 13/16" sparkplug socket.

[bgallinger]

Originally Posted by pjShap

I had a coolant cap leak like that and replaced the cap. Not cheap from Yanmar. That was not the problem. The tabs on the filler neck were bent and not holding the cap on properly. Adjusting those tabs eliminated the leak.

Thank you pjShap!! Hallelujah! I also replaced the fill cap and still had leaks. I followed your advice (thank you again) and bent the clips a tiny bit, used the original fill cap (not the aftermarket one I bought later) and NO LEAK!

I should fess up and come to Jesus on this issue. My problems began a year ago when I did not replace the impellor as I normally would every year. Sure enough, two blades broke off the impellor and lodged themselves in the hose to the heat exchanger. That's when all of this began.