Home Fleetwatch 2010 It’s not anti-freeze! It’s…!

It’s not anti-freeze! It’s…!

Where the cooling system expansion tank is mounted upright behind the cab, coolant levels and colour are easily seen. A non-standard coolant will be clearly visible. And remember that a cooling system expansion tank is not just there for quick visual inspection and driver convenience. The expansion tank removes air from the cooling system.

Watching a driver top up the radiator expansion tank on a new UD460 using a 2-litre Coke bottle filled with tap water only serves to reinforce the need for discipline and training in conducting pre-driving checks, especially when it comes to coolants writes FleetWatch technical correspondent Dave Scott.

There are a lot of things wrong with the Coke bottle filling method described in the introduction to this article. Firstly the system coolant , not anti-freeze , is being diluted with plain water. Secondly, tap water is not recommended for mixing with coolant and thirdly, sealed systems incorporating expansion – or header tanks – only require topping up when they leak.

And then there’s the point that surely a new truck does not leak. Is this not perhaps a case of merely overfilling to start the day, creating excess system pressure and future failures?

Fleet audits reveal an alarming lack of attention to coolant ratios. It varies from plain water to 30% – but seldom indicates a standard of 50:50 which is what most modern engines demand. And then the header tanks also show different coolant colours which means various brands of coolant are being used. This can become a chemical porridge leading to engine failure.

Just because coolant is loosely and incorrectly referred to as anti-freeze, the tendency is to use it only during winter when, in fact, a 50:50 premix ratio should be consistently used all year round for the more important reasons of corrosion and heat. Coolant inhibitor would be a more accurate terminology.

‘˜Anti-freeze’ actually does far more than lower the freezing point of engine coolant. This is what coolant inhibitors are designed for:

  • Remove excess heat from the engine.
  • Increase coolant boiling point.
  • Protect engine components against corrosion.
  • Prevent wet diesel engine sleeve liner cavitations; and finally….
  • Protect the engine from cold weather freeze damage


Just stick to the OEM spec

Original equipment manufacturers (OEMs) are very specific about the type of coolant used in their engines – whether petrol or diesel – and refuse warranty claims where non-specified coolant has been used. Given this, great care must be taken in not mixing incompatible coolants or adding an inappropriate coolant for a truck application. Because the right additives are missing from typical over-the-counter automotive coolants, they should not be used in heavy-duty truck applications.

Coolant is clear when manufactured and a dye – ranging from dark green to bright pink , is added for colour. Coolant cannot be identified by colour alone and maintenance decisions should not be decided by colour. What the colour does is to make it easy to inspect a fleet of trucks where the cooling system expansion tank is mounted upright behind the cab and coolant levels and colour are visible. A non-standard coolant will be clearly visible.

Tap water is a no-no

Very often borehole or tap water is premixed with coolant which is not good enough.

Engine manufacturers recommend that only deionised water is used in a pre-mixed ratio with coolant inhibitor. Deionised water has been filtered or treated to remove ions.

There may be other materials still in the water but the ions , which could interact with chemicals in the coolant , are removed. Chemicals found in drinking water form scale and scaling creates hot spots, insulating the metal which then causes uneven cooling. Cylinder head scale can totally destroy an engine by causing overheating.

Air in the system leads to liner failure

A cooling system expansion tank is not just there for quick visual inspection and driver convenience. The expansion tank removes air from the cooling system.

Air in cooling systems forms bubbles and steam pockets that attack cylinder liners. In untreated systems, imploding bubbles of air bore through steel liners. It’s aggravated by the vibration of the liner caused by piston movement. Nitrite in a coolant prevents cavitations/erosion. Nitrite in treated systems blocks imploding bubbles of air but firstly, all air must be removed via the expansion tank.

Standing orders

Attending to truck cooling systems is part of a job description , it must not happen in a casual and inconsistent way. The one part of this duty falls on the driver during his pre-trip check and the other must be included for workshops and service personnel. There is no point in the driver getting the levels correct when workshops are using the wrong spec.

While coolant systems and specifications vary between truck manufacturers, here are the most common things to observe:

  • Use a 50/50 coolant/deionised water mix all-year round.
  • Always top up with a premixed solution , not with water.
  • Check the coolant level daily and check for coolant system leaks.
  • Keep external intercooler/radiator fins free of debris , insects and grass.
  • Check for bent or missing fan blades and for a proper fan shroud.
  • Check drive belts and pulleys.
  • Check hose clamp condition.
  • Check the radiator pressure cap , not just the presence of a cap but its ability to keep pressure.

And remember: Truck coolant inhibitor consumption should be consistent all-year round. If coolant usage accelerates in winter, there’s something wrong.


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