Coolants & Antifreeze

“Antifreeze” is a misleading word in Karachi. Freezing is not the problem here. What coolant actually does, every day, is carry heat out of the engine faster than plain water, raise the boiling point so it does not flash to steam at the hottest point in the head, and — the part that quietly decides how long the engine lasts — stop the inside of the cooling system corroding.

Plain water is the expensive option. It is free at the tap and it costs you a radiator, a water pump, and eventually a head gasket. Tap water brings dissolved minerals that scale up the hottest surfaces, and once a layer of scale is between the metal and the coolant, heat stops leaving. A topped-up-with-water system runs hotter every year.

The three kinds, and why mixing them is a real problem

IAT — conventional, inorganic. The traditional coolant, usually green. Its inhibitors work by coating every surface, which protects well but wears out quickly, so it needs changing far more often.

OAT — organic acid, often called extended life. Its inhibitors only act where corrosion actually starts, so they last much longer. Usually red, orange or pink, but see below.

HOAT — a hybrid of the two, common in European and some Japanese engines, often yellow or turquoise.

Colour is not a standard. This is the single most expensive misunderstanding in the trade. There is no rule that says red means OAT, and different manufacturers dye different chemistries the same colour. Two red coolants can be chemically incompatible. Never choose a coolant by matching the colour already in the radiator. Read the container, or ask us.

What happens when they are mixed is not dilution, it is reaction. The two inhibitor packages can drop out of solution and form a gel that blocks the radiator core and the heater matrix. Many a system has been destroyed by a careful top-up with the wrong bottle.

Wet liner diesels: the one that catches people out

Most heavy diesel engines have replaceable wet cylinder liners, and those liners vibrate as each cylinder fires. The vibration forms and collapses tiny bubbles against the outside of the liner, and each collapse takes a microscopic bite out of the metal. Left alone it eats a hole clean through the liner wall into the cylinder.

The only thing standing between that and your engine is the supplementary coolant additive in a heavy duty coolant. An ordinary car coolant does not have it. If your engine has wet liners — most Cummins, Caterpillar and Perkins industrial engines do — it needs a coolant formulated for the job, and the additive level needs checking, not assuming.

How often, and to what level, is in your engine manual. We will not print a figure here, because it varies by engine and a wrong one is worse than none.