Flushing The Radiator on a Model A Ford

Usually, I try to keep the subject of these articles fairly broad. But this article focuses on flushing the radiator on a 1931 Model A Ford. It was a surprisingly satisfying task.

Checking the Fluid

It was time to put the Model A in storage. But this year, we decided to store it in a facility that was not temperature controlled. A friend reminded me that I should check the radiator fluid to make sure the car would be safe during the cold Illinois winter months. I agreed and grabbed my toolbox on my way to get the car ready for the winter.  Luckily, I already had two different devices for checking the radiator fluid.

One is a simple “eye-dropper” looking device with little, colored beads inside. The beads are made of different materials that either float or sink, depending on the quality of the radiator fluid.

The other has a bulb (like the kind on a turkey baster) to draw the fluid into a clear chamber. Once in the chamber, a floating “arrow” points to a dial to indicate the quality of the radiator fluid.

I removed the radiator cap when the engine was cold and tried both testers. Sure enough, both testers indicated that the radiator fluid would only protect the engine down to 25 degrees Fahrenheit. Not good.  Since the car is in a non-heated garage and temperatures in this town (in the winter) get down to -10 degrees Fahrenheit or less, I knew I would have to do a complete flush of the radiator fluid.

Preparing to Flush the Radiator

Luckily, the Model A is a very simple car. There is really not much to the mechanical workings of the vehicle. The radiator is easy to get to from both sides. So, I just had to get a three-gallon bucket to catch the old radiator fluid, a hose, and some new radiator fluid to add back into it.

My car has a piece of depressed metal shielding that creates a valley to guide the old radiator fluid into the bucket. This is directly under the petcock valve that you unscrew to let the radiator fluid drain out. Easy, right? Well, yes, but it’s a slow process.

Draining the Old Radiator Fluid

I opened the petcock valve, and a tiny stream of fluid emerged. It flowed into the bucket very nicely.  But it was VERY slow. So I went in and got my phone. I used my music app to play some 1930s style music to set the mood.  It was actually kind of fun.

Fast forward to 15 minutes later. The bucket was barely filled. So, being impatient, I decided to speed up the process. I removed the flexible rubber connector pipe between the radiator return and the engine. Eureka! The radiator fluid gushed out in a messy torrent. The bucket caught most of it, but what a mess!  I was also afraid that my dog would lick up the spilled fluid on the driveway. But the good news is that it drained almost instantly. The fluid was a muddy brown. Awful! It definitely needed to be flushed.


I replaced the hoses and filled up the radiator with nothing but fresh water.  I then ran the car for about 30 minutes or so on nothing but water. After letting the engine and water cool for a little while, I removed the flexible rubber hose again and out came the water.  It was still pretty bad. So I repeated the routine until the water came out fairly clear.

I’ve heard of people who flush the radiator with straight vinegar or professional radiator cleaners. I think I will need to do this next year. But, unfortunately, I was short on time. So, I just flushed the radiator with water. I then replaced the hoses and was ready to fill it with new radiator fluid.

Finishing Up

I added the three gallons of pre-mixed radiator fluid.  Normally, I buy and use the concentrated fluid and mix it 50/50 myself. But this time, I wanted to make sure I had the mix exactly right.  I wanted the maximum protection.

After refilling the radiator with coolant, I started the car.  I ran it and drove around for about 30 minutes or so.  When I got back, I topped off the radiator and checked the fluid again.  Now the testers indicated that the engine would be protected down to -25 degrees Fahrenheit. Much better!

I hosed down the driveway to dilute any remaining radiator fluid since it is poisonous, but animals love it. With my puppy, heaven knows she would get into it. So, better safe than sorry.


For about $38 I was able to flush the radiator on the 1931 Model A Ford.  I felt a lot more comfortable putting it in storage. And for only $38, that’s pretty cheap insurance.  I highly recommend a radiator flush at least once a year for any vehicle.


Written by Gary Pradel