Changing the boat’s engine’s coolant

Author: Diego Yriarte

Everyone knows the key part for good performance and long life for our marine diesel engine is the good maintenance and regular check out. The main jobs to keep in main are: coolant change, oil change, filters change, etc… 

We remind you that all these jobs it’s necessary to be done by a professional work shop.

Let’s see step by step:

How to change a marine diesel engine coolant from a classic sailing boat

Usually, we would like to have a wide engine room, which makes everything much easier, especially the accessibility. However, the boat we took as reference it’s completely the opposite. It is a classic sailing boat, which as most of these kinds of boats; the engine room is not very accessible. Besides the particularity of the engine room, the Nerissa, has some other particularities, such as the angle installation against the centre line (the shaft alignment is at the port side, instead of the centre line). This is a very special configuration meeting a handicap measurement rule from vintage races.    

The Nerissa, is a classic sloop built in Catieri Beltrami in 1965. In 2004, the engine was replaced by a Solé Diesel MINI-62.


Classic wooden boat, Nerissa, sailing in Barcelona. Photo: Diego Yriarte

First of all, we need to keep closer the manual. Do not go ahead till we’ve read the coolant change section. It is necessary to respect the procedures, quantities, and all those small details which are also important, and we need to keep in mind; such as recommended periods between maintenances.

We’ll star with the cooling system, which in this engine is by a heat exchanger with coolant forced circulation. It is recommended to change the coolant liquid every two years.

The coolant circuit in this case has an advantage. The boiler kit is also connected to this circuit. That made much easier to cancel the two hoses and interrupt the circuit and empty. The most optimal, would be to find a place where to place a bucket, on the lowest possible position, where the hose reach with no problem. If it is not possible to do it with the circuit hose, we’ll have to adapt a hose from the same diameter.


We set the bucket at the place were the heater used to be and we empty the circuit by disconnecting the hoses Photo: Diego Yriarte

Once we have everything on its position, then we turn on the engine and the circuit will get empty (the engine won’t be much longer turn on, so there won’t be risk of overheating).

When we finish the emptying operation, then we’ll connect the circuit again as it used to be for the filling. It is very important to use the coolant recommended by the manufacturer, in order to avoid the corrosion; especially if exist the possibility of frostbite, as the ice expansion, might produce cracks on the circuit walls.


At the top, when removing the lid we can control the level. Photo: Diego Yriarte

The manual will show the right quantities to fill, so we have to control the level during the filling operation. When the circuit is full, then we’ll lock it with the cover. Turn on the engine and control that there are not leaking.

In case we detect a leaking, it is mandatory to repair them as most probably there will be air bubbles in the circuit. If it’s necessary, we’ll repeat the start-up operation till we have control that the level is complete and stable.


A custom measure funnel will help the refilling maneuver. Photo: Diego Yriarte


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This post is also available in: Spanish

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