Reader Question: I want to flush the radiator in my car, how do I do it and why should I?
Thanks in advance,
Mark W.

Mark, the first question that comes to mind is WHY do you want to do this? Red flags go up in my head when customers ask me a "how do I..." question. Some people not only like to diagnose their car problems themselves, but they want to perform the operation as well. This can be a great thing, but only if the diagnosis was correct. If it was not you just wasted your time and money. So my question back to the customer would be "what is the problem you are experiencing, and why do you think this operation will solve the problem?" Boy do I get a blank stare then!

"Flushing" a radiator sounds like a wonderful thing to have done periodically to your vehicle, but what does it actually do? You probably have a mental picture of this high powered jet blast of water mixed with some kind of detergent that removes all the gunk that has accumulated in the radiator, and after doing this procedure your car will not only run "cooler" but... "better", right? I mean this gunk has probably been the source of your "engine robbing performance" in your mini van for months, right? I hate to put a damper on your parade, but we need to talk.

Most radiators today are small, made of light weight aluminum, and crammed so tightly in the front of the car you can barely see it let alone "flush" it. The neck of the radiator (where you pour in the antifreeze) is usually angled in such a way that it is impossible to pour in the antifreeze, or even SEE the antifreeze for that matter.

The inside of the radiator is made up of a honey comb maze of rows, or "sipes" that sends the hot antifreeze on a long meandering journey from left to right of the radiator. Air is being forced through fins on the outside of the radiator to cool down the antifreeze inside the radiator.

Ok, I hope you are still with me because here is the answer to the question. Where does dirt and sediment accumulate in the radiator, at the top or the bottom? The bottom of the radiator will trap the majority of the rust, dirt and sediment.

You can try as hard as you want to, but you will not be able to remove enough of this compacted material to do any real significance in engine performance. The way the radiator is designed internally prevents the access of any high pressure action that you might be able to insert into the small opening of the radiator neck located at the top of the radiator.

At my shop the term "flushing" the cooling system has been replaced with "draining and refilling" the cooling system. Removing the lower radiator hose, or if equipped use the radiator drain cock to drain out the old antifreeze and replace with the new fluid is essentially "draining and refilling the cooling system."

This of course will only remove any minor surface debris along with the old contaminated fluid, and will probably NOT cure any over-heating complaints you might have been experiencing. Calcium and rust build up within the sipes are the main causes of radiator stoppages, and will cause a over-heating complaint. If this is the case, removal of the radiator from the car for disassembling and rebuilding, or replacing the radiator are really the only two viable options.

Yes, there are many "radiator flush" additives on the market, but most are not to be used in aluminum radiators (which all newer vehicles are equipped with), or just flat out don't work. There are very few (ok, probably only one or two) problems with a motor vehicle that can be solved by the contents of a can.

So, in a nut shell...draining and refilling your radiator with new antifreeze every two to three years WILL help maintain and extend the life of your vehicle, but will probably NOT have an impact on the way it drives, overall fuel economy, cure a major over-heating problem, or improve handling in wet weather.

Also for added maintenance, ask your mechanic to inspect the radiator and heater hoses, and test or replace the radiator cap when replacing the antifreeze.