Brown sludge in overflow tank

Apr 17, 2013
153
Catalina 310 57 Pompano Beach, FL
Have hull#57 with 25xpb engine. Recently noticed brown sludge in the bottom of the antifreeze expansion tank. Has anyone had a similar issue? Could it be rust? See attached picture

Thanks,
Mark
 

Attachments

Last edited:
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Same as a car. Most likely rust. My guess is regular changes should keep it from building up. Others will chime in but you may need to flush the system.
 

Johnb

.
Jan 22, 2008
1,419
Hunter 37-cutter Richmond CA
When I first got my boat there was this stuff with the consistency of jello in bottom the overflow tank. I scraped it out. Now I just rinse it at every coolant change and it has never reoccurred.

Strongly recommend you do routine coolant changes. The first time through I did a double change to ensure the old stuff was all gone.
 

KD3PC

.
Sep 25, 2008
1,069
boatless rainbow Callao, VA
IF you use Dex-Cool, it will gel over time as it has a short life, especially when exposed to air and tap water. Many other products will discolor or rust.

I would drain, flush and refill with a compatible coolant and distilled water, if called for.
 

MitchM

.
Jan 20, 2005
1,011
Nauticat 321 pilothouse 32 Erie PA
i'd definitely go with flush of whole cooling system. the products they make do a good job. while u r at it check all the hoses for cracking or softness, (especially if you've ever had an engine overheat. ) clean out the heat exchanger , put new gaskets on , change engine thermostat . if your engine has antifreeze circulating thru to heat hot water heater water, check those ones too. it's a lot easier to do all this stuff while the cooling system is drained and before you do the calling system flush. other wise these other tasks cause gallons of antifreeze to spill all over the place , when instead u could be sailing and drinking your beverage of choice.