Cat C9 Cooling - Expansion Tank Issue

[jimL]

Hi there,

We have Cat C9 engines with approx. 4,000 hours on them. While at Atlantic Yacht Basin in June, we had a ‘cooling system service” while we had to attend a family event off site for a few weeks. The ‘service’ include changing the coolant, regulator (thermostat), heat exchanger cap, and raw water impeller. When we returned, we traveled a mile or so to let the engines warm up and burp. We added more coolant to both engines and all was well. Once we travelled 50 NM or so, and let the engines cool off we added a few more quarts of coolant to both engines. Our starboard engine appears, when the coolant heats up, sends the coolant to the expansion tank, but when the engine cools, it doesn’t suck the coolant back into the heat exchanger. The port engine is fine.

I removed the overflow hose from the starboard heat exchanger cap to the expansion tank and blew thru it and was able to blow the coolant into the expansion tank and then air – so I know the tube is clear. When I look at the starboard heat exchanger tank when it is cool, it shows that it is down about an inch (because the heated coolant is still in the expansion tank). I added more coolant to the starboard engine and it again expands to the expansion tank but does not get sucked back to the heat exchanger. Both engines run at 190-192F while running.

Any ideas as to why as the engine cools the coolant is not sucked back into the heat exchanger?

Thanks – JimL
M/V Lemon Drops

 

[sunchaser]

Switch caps between engines. But it will only suck back if no air enters system; maybe a leak in the hose?

 

[Comodave]

Just to clarify, I think you are referring to the overflow tank as an expansion tank. The expansion tank is on the engine and the overflow tank could be on or off the engine and is connected by a small hose. I agree that it is likely an air leak in the small hose or related pieces.

 

[jimL]

Comodave, yes, you are correct. As the coolant expands it's being pushed to the overflow tank and as it cools it is not getting sucked back into the expansion tank.

JimL

 

[Comodave]

Check for air leaks in the overflow plumbing. Could be the hose has a crack or the cap could be bad. Swap caps with the other engine.

 

[Arlen]

Hi there,

We have Cat C9 engines with approx. 4,000 hours on them. While at Atlantic Yacht Basin in June, we had a ‘cooling system service” while we had to attend a family event off site for a few weeks. The ‘service’ include changing the coolant, regulator (thermostat), heat exchanger cap, and raw water impeller. When we returned, we traveled a mile or so to let the engines warm up and burp. We added more coolant to both engines and all was well. Once we travelled 50 NM or so, and let the engines cool off we added a few more quarts of coolant to both engines. Our starboard engine appears, when the coolant heats up, sends the coolant to the expansion tank, but when the engine cools, it doesn’t suck the coolant back into the heat exchanger. The port engine is fine.

I removed the overflow hose from the starboard heat exchanger cap to the expansion tank and blew thru it and was able to blow the coolant into the expansion tank and then air – so I know the tube is clear. When I look at the starboard heat exchanger tank when it is cool, it shows that it is down about an inch (because the heated coolant is still in the expansion tank). I added more coolant to the starboard engine and it again expands to the expansion tank but does not get sucked back to the heat exchanger. Both engines run at 190-192F while running.

Any ideas as to why as the engine cools the coolant is not sucked back into the heat exchanger?

Thanks – JimL
M/V Lemon Drops

As others on this thread are saying, the likely reason it wouldn't recover the coolant back into the engine would be because the cooling system isn't building the vacuum necessary as it cools after shutdown. It'll likely either be a bad pressure cap or possibly a tiny leak in the hose or a fitting on the hose going to recovery/overflow tank. I once had a small pin hole open up in my coolant recovery hose and while it didn't leak when the coolant was going from the engine to the tank, it would allow air into the line later and kept the engine from getting it's coolant back. You can verify either of these possibilities by swapping the hose and cap for the ones on the other engine. Good luck!

 

[C lectric]

Pay attention to Arlen. I goofed and wiped my reply so I will offer my tome
about recovery systems.

 

[jimL]

C letetric - this has been invaluable. I'll give it a try and will let you know how I make out.

Thanks -JimL

 

[Owen Christensen]

Twice now this happened to me. Once last year, coolant in bilge. Pressure test found small crack near filler neck in tank. This year the other engine lost coolant in bilge. It was hole in bottom of tank from touching screw heat from hose clamp.
At least I’m getting use of my pressure tester.