Coolant Airlock or Blown Head Gasket? Refill and Block Test Kits

Fresh coolant in, and now the gauge creeps up and the level keeps dropping. Or the level falls week after week and you suspect the head gasket. A vacuum refill kit helps with the first, and a block tester shows whether combustion gas is behind the second.

The Pressure Test & Refill Kits range at PartsForMachines has 74 products from Sealey, Sykes Pickavant, Draper and Govoni, including pressure test kits, vacuum refill tools, combustion leak testers and antifreeze testers.

Why Does My Engine Airlock After a Coolant Change?

Because air rises to the system’s highest points and stays trapped unless the filler sits higher still. An airlock can cause overheating, and the level keeps falling as each pocket clears.

To bleed it, raise the nose so the filler is the highest point and open any bleed screws the vehicle maker lists. Run the engine with the heater on full hot until it reaches temperature and the thermostat opens, then let it cool and top up to the mark. Never take the cap off a hot, pressurised system. For the refill itself, a non-spill coolant filling set such as the VS0045 comes with Ford and GM adaptors, and Sealey says its rotary switch stops overfilling and air bubbles.

Is a Vacuum Coolant Refill Kit Worth It, and How Does It Work?

Yes, if you refill cooling systems often or work on engines with hard-to-bleed high points. Workshop air pulls the drained system into a vacuum through an adaptor on the filler neck or header tank, as on the VS0042 vacuum purge and refill kit.

Watch the gauge before you fill: if the vacuum falls, there is a leak to fix first. If it holds, open the coolant valve and the vacuum draws premixed coolant in. If you only top up now and then, a non-spill funnel and careful bleeding will do.

Block Tester Turned Yellow or Green: Is It the Head Gasket?

It may be: yellow means combustion gas is reaching the coolant, which can come from a failed head gasket or a cracked head. The tester shows the gas, not its route. Blue means none was found.

Don’t treat green as a pass: the fluid turns green before yellow, so CO2 is still present. Test with the engine running, drawing the air above the coolant through the fluid. If in doubt, retest with fresh fluid. A blue-to-yellow tester such as the 23257 combustion gas leak detector sits on the radiator opening with a cone or pressure test kit adaptor.

Universal Cones or Vehicle Caps: Which Test Kit Should I Buy?

Buy for the vehicles you work on. Vehicle cap adaptors suit only the vehicles they are made for, while cone or bladder adaptors seal a spread of neck sizes, so fewer pieces cover more vehicles.

A cone kit such as the VS0033 seals screw and bayonet necks in four size ranges between 17 and 48.5mm. The VS0014 13-piece pressure test kit has both systems, and Sealey says its bladder seals 90% of cars and light commercials. For trucks, choose a commercial kit such as the CV0011.

What Should I Check Before I Buy?

• how your vehicles’ systems open: radiator cap or expansion tank, screw or bayonet, and neck size
• whether your compressor can run an air-powered refill tool
• whether the block tester connects through your pressure kit’s caps or needs a cone
• cars and vans, or trucks, tractors and plant that need commercial or XL caps and testers
• spare reaction fluid, and an antifreeze tester that matches the coolant base

Browse the Pressure Test & Refill Kits range, or contact the PartsForMachines team by WhatsApp, telephone or email with a photo of the expansion tank and cap.

Product options, delivery options and returns terms are shown on each product page. A 30-day return policy applies to eligible items.

Frequently Asked Questions

Will my compressor run an air-powered coolant refill tool?

Compare the tool’s air figures with your compressor’s output. The VS0042 uses 12cfm at 90psi and the VS0041 12cfm at 80–100psi, both through a 1/4in BSP inlet. On a typical vacuum filler, the air is shut off once the vacuum is reached.

How long should the vacuum hold before I fill?

Watch the gauge for several minutes, up to about 10. A steady needle means the system is tight. If it falls, check the adaptor seal, then look for cracked hoses, loose clips or an open drain tap. Some hoses pulling flat is normal.

Can I vacuum fill with antifreeze concentrate?

Premix it in a clean container first, as the tool draws it straight into the system. Keep the hose end under the surface the whole time, and close the valve to top up the container before it runs dry, or air gets drawn in.

Will I still need to top up after a vacuum fill?

Usually a little. Run the engine, let it cool, then check the level against the mark and top up. Where the vehicle maker gives a bleed routine for the engine, follow that as well.

Will a refill tool work if my car has no radiator cap?

Yes. Refill tools such as the VS0042 attach at the header tank with one of the supplied adaptors. The low-profile VS0041 can also connect to the reservoir through matching pressure test caps, and suits MPVs with a low windscreen lip.

Can one set of adaptors serve the pressure tester, block tester and refill tool?

Often, within one maker’s range. The VS0062 block tester and VS0041 filler both work with caps from several matching pressure test kits, and the 23257 takes a cone or its maker’s radiator test kit adaptors. Check the kit numbers on each product page first.

Will a block tester work on a diesel truck, tractor or digger?

Yes, most block testers in this range suit petrol and diesel engines. For bigger systems, the 33145000 XL combustion leakage tester is designed for HGVs and connects to XL cap adaptors made for trucks, farm and construction machinery.

Do I need to lower the coolant level before a block test?

Yes, a little. With the engine cold, drain some coolant to leave an air space at the top where gas can collect. Liquid coolant must not get into the tester. Never open a hot system, as it is under pressure.

Do I need a different antifreeze tester for propylene glycol coolant?

Usually, with a float, disc or hydrometer tester: most are made for one coolant base, such as the AK4120 for ethylene glycol and the AK4122 for propylene glycol. A refractometer such as the 03201000 reads both.