Q Can you use a wet-dry vac to evacuate antifreeze from a radiator with no drain plug?
A No. It’s a clever thought, but sadly it’s not realistic or good for the engine. First, you don’t want toxic antifreeze in your wetdry vac; when it dries it leaves a sticky residue that won’t be fun to have in your vacuum. Second, because of the way radiators are made, you’ll never remove all the coolant or the gross sediment that builds up inside. For these reasons, it’s best to let gravity do the work and empty the coolant from the bottom.
If your car doesn’t have a drain plug, pick out the lowest hose in the coolant system and loosen the clamp holding it in place. Before you pull the hose off, position a large bucket beneath the radiator to collect the old stuff. Now disconnect the hose and direct the fl ow of coolant into the bucket. It’s a good idea to have a second bucket handy – you never know how much fluid is going to come out. You may also need to remove a plug in the engine block to get even more out; that varies from car to car.
To do a complete flush, reconnect the lower radiator hose and fill the system with clean distilled water. Run the engine for a few minutes until the cooling fan cycles on and off a couple of times. This prompts the thermostat to open and coaxes the coolant in the heater core to cycle through the rest of the system. Shut off the engine, wait for it to cool, and drain the fluid out as you did before. Be sure to properly dispose of the used coolant – remember, this stuff is deadly for pets, children and other living things (check with your local municipality or the ROSE Foundation at rosefoundation.org.za).
Now you can replace the coolant. Check the owner’s manual to make sure you use the correct type. There are variations in colour – green and orange are two options – and chemistry, and coolants should never be mixed. The incorrect option can react very badly with the gaskets and the surfaces in your engine. Since there’s bound to be some residual fluid in the cooling system – it’s nearly impossible to drain the engine block – find out the coolant capacity, but realise you’ll have to fill as needed. Add coolant and water alternately – a 50/50 mix is usually recommended – until the level reaches the top of the overflow tank or radiator.
When it’s filled, start the engine and let it run. The water pump will pull the coolant through the system. Add water and coolant as necessary to keep it filled. Once again, you’ll want to keep the engine running long enough to open the thermostat so the heater core fills up.
One final note: I typically use distilled water rather than the stuff from the tap. The minerals and purification chemicals in tap water may lead to corrosion and scaly buildup in the engine. Premixed coolant is also available. It costs more, but it is convenient.