Overheating fixes
Diesel engines are designed to operate at a temperature of around 85oc. This is only a few degrees shy of boiling point, so the line between happy and steamy is a fine one.
Most ti inboard b d engines i have h t two, separate t cooling li components: the internal system, which circulates coolant in a closed loop within the engine; and the raw-water system, which pumps seawater through a heat exchanger to absorb heat from the internal coolant. The heated seawater exits the boat through the exhaust.
Both systems have a water pump for moving the fluid around. The raw water pump generally uses a rubber impeller to provide a steady volume of cool water, while the internal system has an embedded coolant pump inside the engine.
The two water streams come into thermal contact with each other through a heat exchanger. It’s fitted with numerous thin copper tubes for transferring the heat from the coolant to the colder raw water. In addition, a thermostat adjusts the volume of contact between the engine coolant and the raw water system, closely controlling the engine’s temperature.
Although the engine cooling system is a tried-and-tested solution, every boatie has an overheating horror story. There are several possible causes.
A common one is when the intake of raw water stops – usually because the water inlet is blocked with debris, or the pump impeller has failed. Even mechanically-challenged boaties should know how to check and clear the flow of raw water. Every boat should have a replacement impeller (and the tools to swap it out) on board.
A malfunctioning thermostat is another culprit. Symptoms include: • The engine fails to get to operating temperature within about 10
minutes. • The engine gets too hot quickly, even when under little or no load • The temperature cycles up and down while running under constant load. Thermostats are reasonably easy to replace but the job’s best done back at the marina or workshop.
HEAT EXCHANGER
But the most common overheating problems arise from a steady decrease in the heat exchanger’s efficiency. This starts as a gradual temperature rise, perhaps only being a problem when the engine is under absolute maximum throttle and load.
You might not notice this if you normally run at cruise revs – but you will on the day you need full power, when alarm bells go and a cloud of steam erupts from the engine. Sod’s Law says this will happen when you are far from home.
The main issue affecting the heat exchanger’s efficiency is material clogging its fine tubes. Seawater contains many dissolved minerals, including salts and calcium carbonate. When this solution is warmed up and then allowed to cool in the heat exchanger, the dissolved material can deposit a coating that can completely block the tubes.
Even a very light coating can cause problems, acting as an insulator and preventing the efficient transfer of heat through the walls of the copper tubes. Note that deposits take place even if you operate your boat exclusively in fresh water.
Cleaning the heat exchanger is a maintenance job you need to tackle from time to time. There are various methods, including manual cleaning (using a metal rod, pushed down each tube) and hydrochloric acid (which dissolves the calcium but does not affect the copper).
Neither of these is recommended, though, because of the risk
of damaging the tubes with rods and the hazards associated with concentrated acids. A better solution involves one of the environmentally-friendly products that are both safer to use and won’t damage other parts of the engine.
The best tactic, of course, is to prevent the deposits occurring in the first place, and one of the most popular antidotes for this is Salt Away. Despite its name it doesn’t remove the salt, but works on a molecular level to prevent the salt bonding to surfaces.
Combined with a corrosion inhibitor, it keeps the rawwater system operating at optimum efficiency. Salt Away can also be used to treat an existing problem, and regular use will remove light scaling although it may not fix serious blockages.
Using the product is simple. When you’re finished boating for the day, add Salt Away to the raw-water stream and run the engine for 30 seconds. The remaining salt water in the cooling system is effectively neutralised and causes no issues while sitting there.
If you already have a blockage problem, though, something stronger may be needed to remove it. Ovlov Marine is the agent for Barnacle Buster, designed to be run through the raw
water system once or twice a year. This product not only removes calcium, lime and salt deposits, it also kills and dissolves any barnacles, oysters or mussels lurking around your water intakes.
This system works best when run through a ‘recirculating’ system. Close the stopcock on the water intake and place the end of the intake pipe in a large bucket of Barnacle Buster mixture. The discharge hose, where the now-warm seawater normally discharges through the exhaust, is also disconnected and fed into the same container.
Start the engine and let it idle, with the product circulating through the heat exchanger – intermittently for up to four hours – to completely clean out the raw water cooling system.
RYDLYME
If you need a bigger gun for very heavy deposits, the product of choice is Rydlyme. Popular with commercial operators, users claim it will clean out tubes that are even 90 percent blocked. The product is non-toxic and fully biodegradable. d d bl
We used this product on our project boat, where very heavy deposits had occurred and some tubes were completely blocked. A similar recirculating system is set up (as for Barnacle Buster) and a treatment time of two to four hours is indicated. At the end of the treatment all tubes were completely clear, and the inside of the heat exchanger looked almost new.
No matter which product you use, it’s also a good idea to check the anodes inside the heat exchanger. These are the hardest-working anodes on your boat, and they disappear at a surprisingly fast rate. If the anode is more than 50 percent depleted it should be replaced.
INTERNAL SYSTEM
Having checked all this, sometimes the engine still runs hotter than it should. What’s often overlooked is the other side of the equation: the closed-circuit internal cooling system.
It’s often assumed that the coolant is sufficient to prevent problems on the freshwater side, but the internal water channels can also develop a coating. While not as big a problem as on the raw-water side, the internal coolant system should also be flushed and descaled occasionally.
The process involves draining the existing coolant and flushing the system with fresh water. Fill the system with a product like TRAC’S Descaler – also available from Ovlov Marine – and run the engine intermittently over a period of at least four hours, ensuring it gets up to full temperature and the solution gets into every part of the system.
Drain the product (note, it can be retained for re-use) and follow this with a couple of fresh water rinses. Lastly, a flush with a neutralizer completes the job, after which the engine is again refilled with fresh coolant. Don’t be tempted to re-use the old coolant: replace it with fresh.
And hopefully that will be the end of your overheating problems – for this year at least! B