Head Gasket Test Kit

Most head gasket breaches are above one of the combustion chambers, into the water jacket. Combustion gas then leaks into the cooling system and collects at the top, in the radiator's top tank or the expansion tank, which is the bubbling you may see in the radiator water. The 246 tester detects that gas very accurately, even when there's no real noticeable bubbling and the other signs of head gasket damage aren't obvious.

It's made for small to medium breaches. A large breach produces volcanic bubbling and high cooling system pressure, which stop the kit working, but a breach that size already shows obvious signs and doesn't need a test.

It works on any liquid-cooled internal combustion engine: petrol, diesel or LPG. It does a similar test to the expensive equipment garage mechanics use, so it's also a second opinion on what your mechanic has told you.

A small leak, confirmed

The animation at the top of the page is from a video of a test on a vehicle with a suspected small head gasket breach. Apart from overheating, it showed no other signs of head gasket damage. The tester is in the expansion bottle, with a bottle of the red test fluid beside it. After about ten minutes of idling, enough combustion gas had built up in the expansion bottle to bubble through the tester and turn the red fluid yellow: a positive result.

Your options are to repair the head gasket chemically or replace it. A replacement costs between $2,000 and $10,000 depending on the make and model, mostly in labour, and if the car is worth about the same, it's often easier to send it to the wreckers.

Most head gasket damage is minimal and doesn't need a new gasket. With 245 Blown Head Gasket Repair you should be able to fix it yourself in a few hours, for a bit more than $100, and the repair should last for years. How hard the radiator water bubbles shows how big the breach is and how likely the repair is to work; the 245 page shows the four levels.

Most head gaskets fail from years of cooling system neglect rather than a single overheat: water or low-glycol coolant causes cavitation erosion and corrosion that wear the gasket away. After a repair, 500 coolant is made to stop cavitation erosion and protect the rest of the gasket.

Preparing the leak tester

Remove the top lid segment of the leak tester from the main chamber. Half fill the chamber to the fill line with the red test fluid, and reassemble.

There are two test methods. The first detects or confirms small to medium head gasket breaches. The second is for when there's no real noticeable bubbling in the radiator water, or the other signs of head gasket damage aren't obvious.

Don't let coolant splash into the leak tester. It contaminates the test fluid and stops it working.

First test method: small to medium breaches

1. Open the radiator cap after the vehicle has cooled.
2. Check there's enough air space in the top of the radiator. The coolant needs to be about 25mm below the radiator cap fitting, so the rubber end of the tester can seat snugly inside the filler neck without touching the coolant. Correct the level if you need to.
3. Insert the rubber end of the leak tester into the radiator filler neck.
4. Start the vehicle and let it idle: about 10 minutes for a petrol engine, or about 15–30 minutes for a diesel.

As combustion gas collects at the top of the cooling system, it bubbles up through the fluid in the tester and causes a chemical reaction. If combustion gas is there, the red test fluid turns yellow: a positive sign of head gasket damage.

If the fluid stays red, that's usually a good sign there's no head gasket damage. A negative result can occasionally be wrong, though, because some breaches only open once the engine reaches its hottest full running temperature. That's why we always suggest the second test as well, at higher temperatures and combustion pressures.

Second test method: no obvious bubbling or other signs

1. Open the radiator cap slowly after the vehicle has cooled, and check the air space as in the first method.
2. Remove the top lid segment from the tester's main chamber, fill the chamber up to the fill line with the red test fluid, and reassemble.
3. Push the rubber end of the tester into the radiator filler neck so it seats snugly without touching the coolant.
4. Start the engine and idle it up to full running temperature, then accelerate about 10 to 15 times. After each acceleration, let the engine slow for a few seconds before throttling up again.

This creates high combustion pressures and simulates full driving conditions, with all the engine's tolerances expanded. If the red fluid turns yellow after 10–30 minutes, the tester has detected combustion gas: a breach in the head gasket above a combustion chamber, into the cooling system's water jacket. This kind of damage is very common.