How do I change the coolant on a Volvo Penta D2-50?

To change the coolant on a Volvo Penta D2-50, drain the cold freshwater circuit, close the drains and refill slowly with the correct coolant, then warm the engine and check the level again once cold. First identify the coolant specification already in use and check whether a calorifier is connected, as these determine compatibility and the draining and bleeding procedure.

Check the coolant specification

This job covers the sealed freshwater circuit, which carries coolant through the engine and heat exchanger. The seawater circuit, including the raw-water pump and exhaust injection, is separate.

Check the operator's manual for your engine's serial number, along with the coolant label and service records. Volvo Penta has used different coolant specifications, including traditional green coolant and yellow VCS. Colour alone cannot reliably identify an unknown fill. Buy the specified product or an explicitly approved equivalent, rather than a general-purpose antifreeze chosen by colour.

Do not substitute propylene-glycol winterising fluid intended for the seawater circuit. Engine coolant needs the correct corrosion inhibitors as well as frost protection.

• Use ready-mixed coolant undiluted.
• Mix concentrate with distilled or deionised water in a clean container before filling, using the ratio specified for that product.
• The traditional Volvo Penta mixture is 40% concentrate and 60% water, protecting to approximately minus 28°C. Never exceed 60% concentrate. Follow the product instructions where a different coolant specification applies.

Check capacity in your D2-50 manual and allow extra for any calorifier hoses and heating coil. Do not substitute a D2-55 or D6 capacity.

Drain the engine and calorifier

Let the engine cool completely, isolate starting power and put on gloves and eye protection. Opening a hot cooling system can release scalding coolant.

1. Place a collecting container large enough for the coolant beneath the engine and protect the bilge with absorbent pads. Remove the coolant pressure cap slowly.
2. Identify the freshwater drain points on the D2-50 cooling-system diagram. Use the designated engine-block drain and any additional freshwater drains shown. Do not loosen an unidentified bolt on the heat exchanger.
3. Where a drain has a hose connection, attach a suitable hose and lead it into the container. Open the drain and let the coolant empty.
4. Empty any separate coolant recovery bottle. If a calorifier is fitted, drain its engine-coolant hoses and heating coil where the installation permits. Low hose loops can hold old coolant after the engine stops draining.

The calorifier's domestic drinking-water tank does not need emptying for this job. Collect coolant from its engine-heating circuit separately from the drinking-water system.