Yanmar marine 6lya-stp Needs Flush (or more)!!

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I am dealing with a customer boat 2007 Yanmar 6lya-stp 370hp with a neglected cooling system. I tried to drain coolant from block petcock and not a drop.. after inserting 6'' screw drivers into hole came nothing but brown hard sludge... not a drop of liquid! Upper coolant reservoir & heat exchanger top showed rusty brown water, not pretty.

It should be flushed several times to operating Temp & filed with a O.A.T. ELC or Dexcool per Yanmar specs.

What would be a good product to remove sludge buildup???

This engine ran 30 hrs at 80% (2800 rpm) power 400 miles just a few months ago @ 170F with no issues, but I think its a ticking time bomb...

any suggestions?

Thanks,

Capt
 
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non marine engines I'd use prestone super flush or citric acid.

but I dont work on closed system marine engines...
 
White vinegar and citric acid are mentioned al the time.

Cascade automatic dishwasher soap also cleans well.

A closed loop system marine engine shouldn't be too much different than a car/truck.

Does the big Yanmar use dry sleeves or wet sleeves?
 
Not Sure about the sleeves. I believe the issue is from old coolant or possibly mixing of incompatible coolants as I noticed a jug on the boat with a missing label, who knows... We have not noticed any coolant loss or gain so hopefully the system is still intact, I will probably do a leak down test. I will start with an automotive radiator flush and report back. Thanks -capt
 
FleetGuard make a product, Restore/Restore+ for cleaning cooling systems. I've used it and it works very well.
 
Hello all, I was able to clear the clog with compressed air and a few ounces of mush blew out along with grayish brownish water, All drained out. Added some tap water and ran engine for 20 mins (165 F holding) and cleanish water came out, no sludge. Drained and added tap water and 2 bottles of Zerex super cleaner, ran for 2 hours (160 f holding), took sample from low petcock (pictured). Will run engine tomorrow for an hour and take another sample. I will probably drain, flush with distilled water & add Dexcool tomorrow. Yes I did notice a 5 F degree drop after adding Zerex super cleaner. - capt

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