Is your vehicle running hot?

Or is the heater suddenly blowing cold air?

Or perhaps you've noticed a greenish-colored puddle under the front of your vehicle?

Whatever the symptom, if you've got a leaky radiator, you've got a critical problem that will leave you stranded and destroy your motor.

Frustratingly, trying to seal a radiator leak is just a temporary fix. To prevent lots of angst and expense for yourself, it's best to have the leak professionally repaired or replace the radiator altogether.

However, if you find yourself in a situation where you need to fix the leak yourself, we've got some tips to help you get a good seal that will hold from point A to B!

A Leaking Radiator Will Damage Your Engine

Before we get into the actual sealant options, it's important to highlight how important your radiator is to the car's proper functioning - and how much damage a leak can cause.

How Does A Radiator Work?

A vehicle's cooling system circulates a liquid called coolant through the engine. This works by keeping that coolant flowing through channels in the motor, absorbing the heat produced by burning fuel and high friction. It's then pumped to the radiator to cool off.

The radiator is one of the key parts of the cooling system. It's located in front of the engine, just inside the grill, along with the cooling fan. This radiator is made of hundreds of vertical metal chambers called fins. The (extremely) hot coolant circulates through these fins, allowing it to cool off in the air blown by the fan.

The coolant then flows back to the motor to absorb more heat, before being pumped back through the radiator to cool again.

Damage That A Radiator Leak Will Cause

When your radiator develops a leak, its coolant levels drop. This means the water pressure in the cooling system drops and there is little to no coolant available to circulate through the engine.

The engine will quickly begin building heat from friction and combustion. If you continue to drive a vehicle that's low on coolant because of coolant leaks, the motor will overheat and severely damage your car.

Some of the (extremely expensive) damages you may experience from an overheated engine include:

Engine detonation

Also known as the dreaded "engine knocking," engine detonation destroys the rings, pistons, and rod bearings. If your engine overheats to the point that it's knocking, you will face major repairs.

Warped or Cracked Heads

Both aluminum and cast iron heads will suffer from the intense heat of an uncooled engine. Warped or cracked heads result in an instant loss of power, and leaks inside your motor.

Blown Head Gaskets

As the heads overheat and swell, they can unseat and break the gaskets underneath. This leads to the mixing of oil, gas, and/or coolant inside the engine. This will gaud the pistons, destroy the rings, and be an especially tedious and costly repair job.

Cracked Block

Just as the heads will swell and crack when they overheat, so too will the engine's block. A cracked block is a death sentence for an engine.

Heater and Radiator Hoses

The intense heat and low coolant levels will actually boil the coolant as it's circulating. This can damage the hoses of the coolant system. It can also cause steam to build up and blow the hoses off under the hood. If you experience a sudden blowing sensation in the gas pedal accompanied by a huge cloud of blowing steam and hot liquid under the hood, you've probably blown a hose.

These are all serious mechanical challenges that are best to prevent if you can.

Another serious consideration is that it's critically important to keep coolant or antifreeze from leaking into the environment. Not only is it terrible for ecosystems, it's also incredibly poisonous. Pets and children are especially vulnerable to tasting or swallowing antifreeze because it has a sweet taste. This is a gruesome and often fatal poisoning situation that must be prevented at all costs.

If you find puddles of antifreeze under your car, clean it up immediately using kitty litter, sawdust, or paper towels. That process can help keep everyone safe.

It's important to incorporate regular checks on your coolant system into your routine maintenance, as well as keep an eye on the temperature gauge as you drive so that you can catch and fix radiator leaks as quickly as possible.

Now, let's discuss how to seal a radiator and the best radiator leak sealant.

What Is the Best Radiator Leak Sealant?

When it comes to repairing a radiator leak, all options are temporary, and each has pros and cons. One of the first things you want to consider when you're trying to choose the best radiator sealant for your situation is the type of minor leaks you have.

Is it a crack, rip, or hole? Do you see signs of tiny pinholes causing drips of coolant to seep out? Don't forget to check the coolant reservoir, hoses, and underclamps for the source of the leak as well. Once you identify the leak, clean and dry the area well so that your sealant can bond to the radiator's surface and seal it properly.

Liquid Coolant Additives

One common solution for a leaking radiator is to pour a liquid formulation into the radiator and run the vehicle to heat the product and seal the leak.

This type of product is useful for tiny pinholes that develop in the fins from rust and corrosion. There are many popular, highly-rated products to choose from that are likely to hold a good seal for a long time.

Common complaints about these types of liquid additives are that they can cause clogs in the cooling system that lead to overheating and expensive repairs and that they have a tendency to gum up inside the radiator so that no amount of flushing will rinse the residue completely away.

RTV Silicone Radiator Sealant

Silicone offers an extremely versatile, patch-style coverage for cracks, holes, and leaks of all kinds. Our Hi-Temp Red & Blue 100% RTV Silicone Sealant and Gasket Maker is a fantastic radiator leak sealant, thanks to its superb adhesion, flexibility, and durability under high temperatures. It comes in a classic tube with a resealable nozzle and will withstand temperatures up to 550°F continuously or 650°F intermittently. You can get tubes in both red and blue silicone.

You also might consider our Xtreme Gasket 100% RTV Silicone Sealant Gasket-Maker. This spray-on formulation is incredibly handy for sealing up cracks or holes in the fins of a car radiator. This incredibly versatile product is designed especially for high-temperature and high-pressure conditions.

Each of these RTV silicone products offers superior-quality adhesion, rugged durability, and easy application.

Remember, though, that any DIY radiator leak sealant is a temporary measure. If you decide to use a silicone radiator sealant, consider getting your car to a professional mechanic for a more long-term repair.