Quick answer
Most cooling system jobs need only a few tools. For a top-up or refill: a spill-free funnel and a coolant tester. For a flush: add a drain pan and a flush cleaner. To diagnose overheating or a warning light: an OBD2 code reader, an infrared thermometer and a pressure tester. Work on a cold engine, never open a hot cap, and keep used coolant away from children and pets.
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Key takeaways
- A spill-free funnel is the single most useful tool: it makes refilling and bleeding air out much easier.
- A refractometer is more accurate than a float tester and has separate scales for ethylene and propylene glycol.
- An OBD2 reader shows coolant temperature codes and live temperature, but a code points to a circuit, not a failed part.
- A pressure tester finds leaks you cannot see. Never pump beyond the pressure rating on your cap.
- Used coolant is toxic. Catch it in a sealed pan and take it to a recycling drop-off.
The short list
| Tool | What it is for | When you need it |
|---|---|---|
| Spill-free funnel | Filling and burping air out | Every refill, flush or hose job |
| OBD2 code reader | Reading codes and live coolant temperature | Warning light, temperature gauge problems |
| Refractometer | Accurate freeze protection and glycol % | Checking or correcting your mix |
| Antifreeze tester (hydrometer) | Quick freeze and boil-over check | Before winter, after a top-up |
| Infrared thermometer | Surface temperature of hoses and housings | Suspected thermostat or radiator problems |
| Radiator flush cleaner | Loosening rust and scale before a refill | Dirty coolant, overdue change |
| Pressure tester | Finding leaks under pressure | Losing coolant with no obvious drip |
| Drain pan | Catching and storing used coolant | Any drain, flush or hose change |
Many parts stores loan or rent pressure testers and some scan tools. Check locally before buying a tool you will use once.
Spill-free funnel
A spill-free funnel locks onto the radiator neck or some expansion tanks with an adapter. Because the funnel sits above the highest point of the system, air can rise out while the engine runs, and coolant stays in the funnel instead of on the engine.
How to use it safely
- Start with a cold engine. Fit the adapter that matches your filler neck, gasket facing down, so it seals without movement.
- Press the funnel (or the extension or elbow, then the funnel) into the adapter.
- Pour slowly so air can escape, and fill the funnel about one third full.
- Run the engine at idle with the funnel attached until the thermostat opens. Do not rev it: high RPM can make coolant erupt. If the level rises a lot, shut the engine off and let it settle.
- If your system has bleeder screws, open them as your service information describes.
- To remove the funnel, use the stopper plug as the maker instructs, then refit the radiator cap. Never let pressure build with the plug in.
More detail: how to bleed coolant and how to add coolant.
Lisle 24680 Spill-Free Funnel kit
Clips onto the radiator or reservoir neck so you can fill and burp air out without spills.
OBD2 code reader
An OBD2 reader plugs into the diagnostic port under the dashboard of 1996-and-newer US vehicles. It reads stored trouble codes and, on most models, shows live engine coolant temperature. Codes P0115 to P0119 cover the coolant temperature sensor circuit, and P0128 means the coolant stayed below the thermostat regulating temperature, often a thermostat stuck open (SAE J2012 definitions).
How to use it safely
- Plug it in with the ignition off, then switch the ignition on as the reader instructs.
- Write down every code and its freeze-frame data before clearing anything.
- Treat a code as a pointer to a circuit or condition, not a part to replace. Low coolant and air pockets can trigger sensor codes.
- Never keep driving with the temperature gauge in the red to "see what the reader says".
See coolant temperature sensor and coolant warning light.
ANCEL AD310 OBD2 code reader
Reads and clears check-engine codes, and shows live coolant temperature on 1996+ OBD2 vehicles.
BlueDriver Bluetooth OBD2 scanner
Phone-app scanner with live data and code reports. Linked as a search because we could not confirm the current listing.
Coolant refractometer
A refractometer reads how light bends through one drop of coolant and shows the freeze point on a scale. Good ones have separate scales for ethylene glycol (most car coolants) and propylene glycol (some "safer" coolants, RV and many data-center fluids), and automatic temperature compensation.
How to use it
- Calibrate: put a drop of distilled water on the prism and adjust it to read zero.
- Take a sample from a cold engine after the coolant has circulated.
- Put a drop on the prism, close the cover, look toward a light and read the boundary on the correct glycol scale.
- Wipe the prism clean.
Use the reading with the freeze & boil calculator or the coolant mix calculator. More detail: coolant tester & refractometer.
4-in-1 antifreeze refractometer (EG and PG scales, ATC)
Reads freeze protection from one drop, on separate ethylene and propylene glycol scales.
Antifreeze tester (hydrometer)
A squeeze-bulb tester draws coolant into a tube with a float or dial that reads freeze and boil-over protection from the fluid's density. It costs very little and is fine for a quick seasonal check. It is less precise than a refractometer, and Prestone's tester is for ethylene glycol coolants only.
How to use it
- Test with the engine cold.
- Draw coolant in until the level reaches the line marked on the tester.
- Tap it to free air bubbles, then read the scale.
- Look at the sample: rust, sediment or a muddy look means a flush is due.
- Return the sample to the system or a sealed container. Do not leave it where pets can reach it.
Prestone AF-1420 antifreeze tester
Cheap squeeze-bulb tester for a quick freeze and boil-over check.
Note: For ethylene glycol coolants only, per Prestone. Less precise than a refractometer.
Infrared thermometer
A non-contact infrared thermometer reads surface temperature from a distance. On a warm engine you can compare the upper and lower radiator hoses or check the thermostat housing: a radiator that stays cool while the engine is hot points toward a thermostat, flow or fan problem. Shiny metal reads low because it reflects heat. Aim at a rubber hose or a painted surface, or put a piece of electrical tape on bare metal. The aiming laser marks only the centre of the area measured. With a 12:1 distance-to-spot ratio, the spot is 1 inch wide at 12 inches, so get close to small targets.
Safety
- Keep hands, hair and clothing away from belts and the radiator fan. Electric fans can start even with the engine off.
- Never point the laser at anyone's eyes.
- Read temperatures; do not touch hot hoses or open the cap to check.
See coolant pump and radiator cap.
Etekcity Lasergrip 774 infrared thermometer
Non-contact surface temperature: compare the upper and lower radiator hoses, or check a thermostat housing.
Losing coolant?
Diagnose a leak →Radiator flush cleaner
A flush cleaner loosens rust, scale and deposits so they drain out before you refill with new coolant. You need it when the old coolant looks dirty or rusty, when a change is well overdue, or when your owner's manual calls for a flush. Check your manual first: some makers specify only a drain and refill.
How Prestone says to use its AS105 cleaner
- Engine off and cool. Drain the radiator and close the drain cock.
- Pour in the whole bottle and fill with water (two bottles for systems over 12 quarts).
- Run the engine with the heater on high for 10 minutes after it reaches normal operating temperature.
- Let it cool, drain, refill with water, and run it again for 10 minutes.
- Let it cool, drain, then refill with the coolant your manual specifies.
Catch all the rinse water: it contains old coolant. See coolant flush guide and coolant flush cost.
Prestone AS105 radiator flush & cleaner
Cleaner you run through the system before a full drain and refill.
Cooling system pressure tester
A pressure tester is a hand pump with adapters for the filler neck. It pressurises a cold system to the cap rating so leaks show up as drips or a falling gauge. A pressure drop with no visible drip can point to an internal leak. Many kits also include an adapter to test the cap and a vacuum tool for refilling without air pockets.
How to use it safely
- Test only with a cold engine, topped up.
- Fit the matching adapter and pump to the pressure marked on your cap. Do not exceed it.
- Watch the gauge for several minutes and look for drips at hoses, the radiator, the pump and the heater hoses.
- Release pressure slowly with the valve before removing the adapter.
Full steps: coolant pressure tester. Losing coolant? See coolant leaks.
OMT coolant pressure tester & vacuum refill kit
Pressurises a cold system to the cap rating to find leaks; the vacuum tool refills without air pockets.
Drain pan
A sealed drain pan catches coolant when you open the drain cock or pull a hose, then closes for transport to a recycling point. Ethylene glycol coolant is poisonous and tastes sweet to pets. Never pour it on the ground or down a drain. Many parts stores and municipal hazardous-waste sites accept used antifreeze, as the US EPA describes.
Keep a coolant-only pan, or clean it well after oil changes. See coolant disposal.
Lumax LX-1632 15-quart drain pan
Catches the old coolant and seals it for the trip to a recycling drop-off.
Repair manual for your car
A model-specific repair manual shows where the drain cock and bleeder screws are, the refill capacity and the bleeding procedure for your engine. Haynes manuals cover particular models and year ranges, so check the coverage on the cover. Your owner's manual still decides which coolant to use.
- Audi: Haynes manuals
- BMW: Haynes manuals
- Jeep / Dodge / Ram / Chrysler: Haynes manuals
- Ford: Haynes manuals
- Chevrolet / GMC: Haynes manuals
- Honda: Haynes manuals
- Hyundai: Haynes manuals
- Kia: Haynes manuals
- Mazda: Haynes manuals
- Mercedes-Benz: Haynes manuals
- Nissan: Haynes manuals
- Subaru: Haynes manuals
- Toyota: Haynes manuals
- Volkswagen: Haynes manuals
- Volvo: Haynes manuals
What to buy first
| Your job | Start with |
|---|---|
| Topping up | Spill-free funnel, antifreeze tester or refractometer |
| Drain and refill or flush | Funnel, drain pan, flush cleaner, refractometer |
| Warning light or overheating | OBD2 reader, infrared thermometer, then a pressure tester |
| Slow coolant loss | Pressure tester (or borrow one), then fix the leak |
When to see a mechanic
See a mechanic promptly if…
- the temperature gauge reaches the red or steam appears: stop safely and let the engine cool
- there is oil in the coolant or milky oil
- you keep losing coolant but cannot find a leak
- the pressure test drops with no visible drip
Frequently asked questions
What tools do I need to change coolant?
A drain pan, a spill-free funnel, the coolant your manual specifies, distilled water if you use concentrate, and a tester to check the mix. A flush cleaner is optional unless your manual calls for one.
Is a refractometer better than an antifreeze tester?
Usually, yes. A refractometer is more accurate, needs one drop and has separate ethylene and propylene glycol scales. A float or dial tester is cheaper and fine for a quick check of ethylene glycol coolant.
Can an OBD2 scanner diagnose overheating?
It can show coolant temperature sensor codes, a thermostat code (P0128) and live coolant temperature. It cannot see a leak, a failing water pump or a blocked radiator, so combine it with a visual check and a pressure test.
Do I need a pressure tester?
Only if you are losing coolant and cannot see why. Many parts stores lend or rent them.
New to cooling systems? Start with how a car cooling system works. Looking for a product? Search the coolant directory or match your manual's spec with Find my car coolant. See also coolant by car make and coolants by brand.
Related guides
Sources
- Lisle Corporation: 24680 Spill-Free Funnel
- Lisle Corporation: 24680 Spill-Free Funnel instructions (PDF)
- SAE J2012 (2016): Diagnostic trouble code definitions (copy)
- Prestone: Antifreeze + Coolant Tester (AF1420)
- Prestone: Total Cooling System Cleaner (AS105)
- Prestone: Changing your antifreeze and coolant
- Fluke: How to get great results with an infrared thermometer
- Engineering ToolBox: Ethylene glycol heat-transfer fluid properties
- US EPA fact sheet: How do I dispose of used antifreeze?