A few bottles of vinegar essence and five hours of work. Descaling the cooling channels of your boat engine significantly extends its service life. Why, contrary to engine dealer’s advice, converting to dual-circuit cooling yet is worth the job in most cases. Here is a DIY instruction on how you achieve this.
Indispensable fresh water cooling and seawater filter
Boats are bought on price. This is why yards save on initially overseen extras that only pay off in the long term. For example, there are many boat diesels with so-called single-circuit cooling. Here the engine is cooled directly by seawater. It will run smoothly for the first one or two decades, while the engine’s cooling channels calcify and become increasingly narrow. The operating temperature rises slightly and unnoticed.
Dual-circuit cooling with heat exchanger on the right – Photo Swedesail
This does not happen with dual-circuit cooling because the engine has an additional heat exchanger where the temperature of the second, inner cooling circuit is kept low by the seawater. Another disadvantage of single-circuit cooling is the fact that the engine never reaches its ideal operating temperature. As long as the cooling channels are free, it runs colder than it should.
500 or €30,000?
Some yards even save €50 to €100 on cooling water filters. Thus, the seawater is pushed through the narrow cooling channels of the engine, including dirt like mussels, algae, or sand. This pays off for the engine manufacturers because it makes a new engine necessary after two or three decades. Today, a new inboard engine of around 30 hp easily costs €20–25,000 with installation and the necessary modifications. The suitable propeller comes on top. A good 4-blade feathering one costs over €4,000. That adds up to around €30,000.
Installation of dual-circuit cooling against expert advice
Having run my Volvo Penta MD17C for eight years, I retrofitted a dual-circuit cooling system at the end of the 1980s, contrary to the Hamburg-based Volvo Penta dealers’ advice. There were two kits available at the time. A cheap one with a separate electric motor, where the engine would have immediately overheated in case of a failure of the electric motor. And the original V-belt-driven kit, which cools the engine reliably as long as the V-belt is in good condition.
I was told, it wouldn’t be worth it and instead, I should rather buy a new boat engine in the foreseeable future. The retrofit at the time is the reason the 1979 engine still exists today. And I soon installed the missing sea-water filter.
This is indispensable when motoring in shallow waters such as the Baltic and North Sea or in rivers, where algae, mussels and swirling sand are common. Both measures required an investment of roundabout a thousand marks at the time, equivalent to €500. The installation took about a day, the installation of the cooling water filter half a day. I mounted the sea-water filter in the cockpit locker, as well as the expansion tank of the inner cooling circuit. At his location, both can be checked easily. This convenience is important for taking care.
Descale your motor
Take half a day to rinse your single-circuit cooled machine using the following instructions. If you are converting to dual-circuit cooling, it is essential to flush the cooling channels.
“If you overheat the exhaust and engine when flushing, you will have done more damage than good.”
As long as the cooling channels are not already blocked, flushing is possible with a vinegar solution. In principle, this is what you do at home when descaling your coffee machine or kettle with the usual 25 per cent acetic acid for 90 cents a bottle. The quantities of liquid mentioned refer to small 2- or 3-cylinder diesel engines with ≈ 14–27 hp (10-20 kW). For larger engines, use more water and acetic acid in the mixing ratio described.
Preparation: 1. take a photo or note the operating temperature at normal speed on the panel so that you can compare it with the temperature after cleaning. 2. you will need suitable hoses (check Ø and lengths) and hose clamps for the flushing installation, as well as a bucket.
Four crucial points
Be careful when dealing with acids like vinegar essence.
The engine must not run for more than one to two minutes during the recommended flushing processes with the vinegar mixture. The exhaust is no longer water-cooled, which means that the exhaust hose and silencer will quickly overheat. In addition, the engine quickly becomes hot due to the small amount of coolant.
It is best to work with a fellow who monitors the running times of the engine using a stopwatch and switches it off in good time.
The bucket with the vinegar mixture must be placed under or next to the engine, never higher; otherwise, water will block the engine and cause the starter motor to burn out the next time you try to start it.
The job takes ≈ 5 hours
Warming up the engine 1⁄4 hour
Flushing preparation 1⁄2 hour
Repeat rinsing with acid mix ≈ 2 1⁄2 hours
Post-rinse work ≈ 1⁄2 hour
Fresh water rinsing & checking 3⁄4 hour
Obtain vinegar essence and mix with water
Use 80% vinegar essence, which is available for around €16 per litre. For an 8.5 litre mixture, you need 850 ml of the 80% vinegar essence and a good 7 1⁄2 litres of water. The bottles of standard 25% vinegar essence from the supermarket, pictured above, contain 388 millilitres with an acid content of 25%. For 25% acid, use around three times the amount, i.e. 3 litres, to achieve the desired acidity of your mixture, and correspondingly less water, i.e. 5 1⁄2 litres.
Step-by-step instructions
Warm up the engine for about a quarter of an hour at a slightly higher idling speed.
Switch off the engine, close the seawater inlet.
Remove the thermostat. Leave the thermostat housing sealing rubbers in the engine and refit the thermostat cover.
Drain the cooling circuit. Close the drain cocks again.
Remove the cooling water intake hose from the seacock, extend it if necessary and lead it to a bucket.
Remove the cooling water return hose upstream of the exhaust feed, extend it and also guide it to the bucket. Attach a nylon stocking or similar close-meshed fabric to the hose outlet in the bucket as a filter screen to catch the escaping dirt with a cable tie.
Mix one litre of 80 percent vinegar essence with 8–9 litres of water to create an 8-10 percent acetic acid solution.
Start the engine and let it run for about 2 minutes so that the acetic acid solution is sucked out of the bucket.
As soon as the acid from the return hose reaches the bucket, switch off the engine. Leave the acetic acid solution to work for 10–15 minutes.
Repeat steps 9 to 10 until there is no more large amounts of dirt in the bucket. At least 8-10 rinsing cycles are necessary. Gas beads rising in the bucket indicate carbonic acid, which is produced as a result of the chemical reaction between the scale and vinegar.
Drain the engine cooling circuit and close the open taps again.
Carry out the flushing with the necessary patience and time to adjust any problems that may arise. Furthermore, larger deposits or dirt may come loose later and block a narrow point in the cooling system. Therefore, keep a close eye on the engine temperature after the operation.
This job requires some hands-on practise and technical understanding. If you are unsure, have it done by a technician. However, be on board for the appointment. This will ensure that it is done carefully. And you see yourself how much limescale and dirt ends up in the bucket. And don’t let anyone talk you into a new engine. You just need a reliably running engine, that one you have.
Although this procedure has been experienced and tested for decades, no guarantee is given for its success or for any damage to the engine. If you have further questions, I will be glad to answer them as part of as the advice I am offering.
Photo on top by Swedesail: Common vinegar essence from the supermarket. Updated 26 May, 25.→ Subscribe Newsletter and you won’t miss future articles.
