Losing coolant or running hot? We find the cause before anything gets replaced

Most cooling system problems give you some warning before they become serious. The common signs we see at the workshop are:

• The temperature gauge sitting higher than usual, or climbing in traffic or on hills
• The coolant level in the expansion tank dropping between checks
• A puddle or drips under the front of the vehicle, often green, pink, orange or blue depending on the coolant
• Steam from under the bonnet, or a sweet smell after a drive
• The heater blowing cold air when the engine is warm
• A temperature warning light on the dash

Coolant going down with no puddle underneath deserves particular attention. It can mean the leak is dripping onto a hot part of the engine and evaporating, or that coolant is being lost inside the engine, which is where a head gasket problem can start to show.

If your gauge is heading towards hot right now, pull over somewhere safe and switch off. Do not open the cap on a hot engine. The car overheating and losing coolant guide walks through the likely causes in order.

A coolant leak repair in Hamilton should start with a test, not a guess. The cooling system runs under pressure when the engine is warm, and many leaks only show themselves under that pressure. With the engine cool, we pressurise the system and watch where the coolant escapes and whether the system holds pressure at all.

Alongside the pressure test we look at the parts that most often cause trouble:

• Hoses and clamps: rubber hoses harden and crack with age and heat, and clamps can loosen
• Radiator: we check for weeping seams, corrosion and damage to the core
• Thermostat: a thermostat that sticks can stop coolant flowing through the radiator
• Cooling fans: a fan that does not switch on often shows up as overheating in slow traffic

Where the symptoms point towards a head gasket, such as coolant disappearing with no external leak, white exhaust smoke or milky oil, we also run a combustion leak test to check for exhaust gas in the coolant. That tells us whether we are dealing with a leak outside the engine or a fault inside it, which makes a big difference to the repair.

Once we have found the cause, we explain what we found, why it happened and what we recommend. You then get a free written quote for the repair, and nothing goes ahead without your sign-off.

Some faults are linked to other work. On many engines the water pump is driven by the timing belt or sits behind it, so if a pump is weeping and a cambelt is due, it often makes sense to do both at once. Our cambelt and timing belt replacement page explains how we handle the water pump on those engines.

If the testing points to the head gasket, we will tell you straight, and our head gasket repairs page covers how that job works. A blown head gasket is usually the result of an engine that has overheated, so we also find out what let it overheat in the first place. Fixing the gasket without fixing the cooling fault just sets you up for the same problem again. Our guide on whether to repair or replace after a head gasket failure is worth a read if you are weighing up the options.

For light commercial vehicles and Class 2 trucks, cooling system flushes, hose and thermostat work are part of our regular commercial vehicle servicing, so a fleet ute or van can have its cooling system looked after at the same visit as its scheduled service.

An engine that runs hot does not usually fail all at once. It starts with a small leak or a sticking thermostat, the coolant level drops, the engine runs a little hotter, and every hot drive puts more stress on the cylinder head and gasket. Left long enough, the head can warp or the gasket can fail, and a repair that might have been a hose or a thermostat becomes a much bigger job.

That is why a dropping coolant level is worth booking in rather than topping up week after week. Topping up keeps the engine going for now, but it does not tell you why the coolant is disappearing, and it can hide a problem that is getting worse.

Regular servicing helps too. Coolant level is checked and topped up as part of every service, and a level that keeps dropping between services is an early warning worth acting on. See our car servicing in Hamilton page for what a service covers, or our diesel mechanic page for diesel servicing.

We do not put prices on the website, because the cost of a cooling system repair depends on what the testing finds. The main things that affect it are:

• The cause: a loose clamp or a split hose is a very different job from a head gasket
• Access: some parts sit right at the front of the engine, others need covers, belts or other parts removed to reach them
• Linked work: a water pump behind a timing belt is usually best done with the cambelt, which changes the size of the job
• Damage from overheating: an engine that has been driven hot may need more than the original fault fixed
• Parts and coolant: the correct parts and coolant type for your engine

Once we have tested the system, we give you a free written quote so you know exactly what is involved before you decide. Call (07) 847 3339 or use the contact form. If you need a quote for Work and Income, see our WINZ quotes page.

Our workshop is at 281 Kahikatea Drive, Frankton, Hamilton. Drivers come to us from across Hamilton, including Hillcrest, Rototuna, Te Rapa and Chartwell, and from Cambridge, Te Awamutu, Morrinsville, Huntly, Ngaruawahia and Raglan.

The workshop is open Monday to Friday, 7:30 AM to 4:30 PM. If your engine is overheating, the best thing you can do is stop driving it and give us a call on (07) 847 3339 so we can talk through the safest way to get it to us.