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My Cummins QSB 5.9-380 Diesel is leaking coolant!

ScottJJones

New member
I have twin Cummins QSB 5.9 diesel engines. My starboard engine is leaking coolant. It only happens when I run at full throttle of 3000-3100 rpms. If I cruise at 2700 rpm's or less it doesn't happen. I've checked the reservoir and the hoses leading to the engine and both are fine. I've had the hoses checked and replaced, a number of mechanics on board and no one can find where the leak is.

Has anoyone experienced this issue?

Thanks
 
Thanks Chris. Just talked to Cummins and they say there is a bleed hole under the water pump and if the pressure gets high enough it will weep. Which explains the leaking only at full throttle. Sound familiarl?
 
If you aren't seeing coolant in the bilge, it must be going out the exhaust. Buick430 above could be on to it if you aren't finding coolant in the bilge. A crack in the turbo exhaust housing can be hard to find.
 
Yes. I just had a bad turbo on a 5.9 QSB on a police/fire boat. using coolant and heavy steam under load from exhaust. Removed turbo and could see the coolant residue on exhaust side of turbo. after spraying the inside down with brake clean several cracks became easy to see.
 
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