Most of the time, you’ll be reusing the old radiator with the new engine. If the original radiator is in good shape, there’s nothing wrong with this. However, if there are problems with the old radiator, you should replace it during the engine installation process.

Engine Installation & Blocked/Worn Out Radiators

The radiator’s job is to cool the antifreeze as it cycles through the engine. As the antifreeze moves through the engine, it absorbs heat and is then sent back to the radiator where the series of fins (with the help of the cooling fan) cools the antifreeze down. It’s then sent back into the engine to do it all again. That’s what happens in a good radiator, anyway, not so much in what you will find in cheap engines and their radiators. However, there’s always the chance that the old radiator isn’t up to snuff.

Heat kills engines, period. Without a fully functional, known good radiator, you’re only setting the customer up for another dead engine. In fact, radiator problems might have been responsible for dooming the original engine in the car. During your diagnostic process, a full evaluation of the radiator is necessary to determine if it’s worth reusing or if you should install a new one.

Checking a radiator for blockages is relatively simple. The “hand test” can be good as a rule of thumb. Warm the engine up to operating temperature, and then turn the car off. Feel the fins on the radiator (but not the top for safety). The radiator’s surface should be the same warm temperature. If there are noticeable cool/cold spots, there’s a blockage in the way.

Another way to test radiator operation is to remove the cap (with a cold engine) and then let it run. Wait for the thermostat to open and the cooling fans to kick on. Using a flashlight, check to see if there is any flow within the coolant. If there is none, or there is only minimal movement in the liquid, there’s a blockage (these tests must be performed on the OLD engine, not the replacement engine).

Age is another issue here. If you’ve got a high mileage car, or one that’s old and it still has the factory radiator, replacing it might be a good idea even if there aren’t any blockages compromising operation right now.

Finally, if the radiator has been used with water or a mostly water mix, it’s a good idea to go ahead and replace it. Rust and corrosion in the radiator can lead to overheating, killing the new engine. It’s always better to be safe than sorry in this area with engine installations.