Loosen the reservoir cap just a little, then step back while the pressure releases. Then, remove the cap completely. If the coolant level is low, add the correct coolant to the reservoir (not the radiator itself). You can use diluted coolant by itself, or a 50/50 mixture of concentrated coolant and distilled water.

Is it OK to put straight antifreeze in your car?

Using pure antifreeze inside your vehicle's cooling system causes that system to lose about 35 percent of its ability to transfer heat versus a proper mixture of antifreeze and water. ... For this reason, you should not run your vehicle on pure antifreeze.

When should you put antifreeze in your car?

In instances where an engine has overheated, causing a breakdown, there may be a need to add fresh coolant/antifreeze to the cooling system. However, you should never add coolant/antifreeze when the engine is hot, and instead, wait for it to cool.