Antifreeze

[ChromeDome]

Annual coolant change seems a bit excessive while every two years seems right .

It is, but I need 10-15 litres of coolant to run through the sea-water side every year, so it is either buying new to pour in and watch coming out of the exhaust or changing the engine coolant and re-use the drained amount by running it through the strainers.

Some years I've had "used but OK" coolant from a car in which case that is used for the sea-water side, and the boat engines are left as-is.
"OK" is when my refractometer shows sufficient antifreeze properties.

 

[Momac]

I don't use antifreeze on the sea water side as the boat is in the water . But have a frost protection tube heater in the engine bay.

 

[PeterWright]

The new inhibitors really do last 5 years and much more (it is both age and hours).

If you see rust, you can bet dinner it is one of three things:

• Air leak. The expansion tank (cars and boats) purpose is to keep oxygen out of the system. Another source of oxygen is a leak in the head gasket (exaust into the coolant). It really takes VERY little O2 to consume additives and greatly accelerate corrosion. Oxygen will cause the glycol to oxidize to glycolic acid, the pH will drop, and the coolant will become very corrosive. A pH test is good way to check for this (compare to the start value, which varies with the coolant type). Also bubbles in the expansion tank.
• Floating ground. Coolant is an electricity, it is circulated, and so it can generate a small electric current which can be drained by proper grounds on all parts of the cooling system, incliding the calorifier. Same problem on cars, some times coming from an improper fan replacement.
• Seawater contamination. Salt is really, really bad for freshwater cool engines. You either have to test or change the coolant every year. I would test every year, but I'm a lab guy.

Many marine engines still don't have an expansion tank fitted as standard, so oxygen in the coolant is normal for those engines - hence the specified high frequency of coolant replacement. Cars have had expansion tanks since the mid 1960s.

Peter.

 

[thinwater]

Many marine engines still don't have an expansion tank fitted as standard, so oxygen in the coolant is normal for those engines - hence the specified high frequency of coolant replacement. Cars have had expansion tanks since the mid 1960s.

Peter.

No, the main reason for the shorter change interval is chloride contamination. But you aren't doing yourself any favors not having a cold expansion tank. If you are concerned about engine maintanance you will add one. I've worked on standards development.