Radiator Coolant Change


Prestone Concentrated Anti Freeze – £20.00

Optional = Radiator hoses if perished – £25 to £50 depending on concorse etc.

Optional = Heater matrix hoses if perished – £25 – £70 depending on concorse etc.

Optional = Thermostat – £15 to £20

What’s in the box:

There is no right or wrong for this section. You can use what ever antifreeze you like, concentrated or pre mixed. I chose Prestone because it will mix with all antifreeze makes out there. The choice really is yours here, just make sure you follow the instructions for the mix you have. I would suggest a branded make though.


The engine on my car was sitting around for twelve years with no water in it. So the decision was to see how the engine runs. We of course added blue antifreeze and water from the outset after a flush out with water prior to hitting the road. I have now run the car for a year with 1,500 miles over the year and the water in the rad was brown and horrible looking now. But the temperature runs slightly less than half way on the gauge and has been superb all summer not even creeping up in traffic. So it decided it was time to change out the antifreeze as a matter of maintenance and precaution.


There are many schools of thought on this and most of them centre around the “pull the bottom hose off” technique. This of course works, but is messy. If the hose is stuck in place you could split it or damage it. Also you will need a couple of buckets to catch the coolant the best part of couple of gallons. On some radiators for Mustangs there is a drain point called “petcocks”. This is a wing nut headed idea with a hole in the centre. Winding the valve INWARDS, you open the seating at the back and the water runs out the front of the valve. A brilliant little idea. Here the valve is mounted on the lower part of the radiator on the drivers (left) side.

The downside to this method of course is the time factor. You are not draining out in one big go, this is a little jet running out.

I soaked the valve with Gibbs and left to soak for a half an hour or so while I got my tools and things ready I would need. I gently rocked the valve to loosen it and it soon cracked free and allowed easy turning. I placed an oil change bowl under the radiator, simply because it’s large and flat with a pour spout. Not knowing how this coolant was going to run out I left the radiator cap on thus forming a little vacuum in the radiator. The water trickled out to start with, unscrewing the rad cap allowed the coolant to flow much more freely with a stronger jet.

As you can see from the pics above it wasn’t exactly clean. As the bowl was starting to fill up, it’s a simple case of shutting the valve and empty the old coolant into a container ready for disposal, no mess and you can take your time. Replace the bowl and start again. Eventually all the water had drained out and then it was time for the wash through. You can use radiator flush at this point if you wanted to too if there was sludge. I just had dirty water so I used the tried and trusted method to run the hose pipe through the rad until the water runs clear. I first filled the rad up to the top and waited for the airlocks to filter out and then opened the bottom valve again. I did this about six times until it was pretty clean shutting the valve again for now.

Next up was the top heater hose located behind the distributor and next to the water temperature sender. Undo the hose clamp as the pipe and heater matrix will be empty now. The problem here is getting the water hose pipe into the block. The hose diameter is too small for the elbow coupling so I came up with a plan. I got my old heater hose and pushed it into place on the elbow, the hose was pointed out the car. Obviously filling up the block will result in the heater matrix hose spilling out water too. Part two of the cunning plan was to cut a small length of old hose pipe and wedged it into the matrix hose which was a tight fit. I then clamped the old hose pipe shut with a little gadget designed for that purpose. As this water was not under any pressure it was more than enough to stop leaks onto the engine and anywhere else. You can see the clamp on the end of the green garden hose.

The garden hose pipe was then wedged into the old heater hose that was now attached to the water elbow, then the water was run into the block. This worked a perfectly and I gave myself a silly grin. The radiator cap was left off still while the water was pouring into the block to allow any air to escape. The water filled back up into the radiator and I stopped when the water level could be seen from the top of the radiator. Open the drain valve and the water comes out dirty again. Repeat the process untill the water is  clean. I left the valve open and managed to regulate the water flow so it came out as fast as it was going in.

The pic below you can see the clean water now running out.

With the valve shut I started the engine with no water for a few short seconds just to spin the residue around from the pump. Again the water was rinsed through the block until clean. Replace the heater hose to the top of the manifold and clamp it up. Make sure the drain valve is shut.

It would be a good time to check your heater hoses for sign of perishing, if they have perished then now would be a good time to replace them before filling up.

Mix up your antifreeze or coolant to the correct formula and then pour into the radiator.

Fill up untill the coolant is just about covers the internal radiator fins. Leaving the radiator cap off for now, start the car up to allow it to warm up. Make sure the heater is set to hot too which will allow water to circulate around and remove any air pockets. The thermostat will open and the water level will drop, top up with more fluid as required. Replace the radiator cap. Take the car for a short run and allow the car to cool down. Recheck the coolant and top up as required.

Time Taken:

This took a couple of hours draining, filling the rad and engine block, emptying the containers and radiator. You could always drain the radiator from the valve then remove the bottom hose for a much, much faster flush, that would be your choice of course. It was a long process for me and gave me an excuse to check over the car and do a little tinkering in the process like changing out old jubilee clips for new ones etc.


There is noticeable difference to see. But, there is brand new coolant in the engine, it should be cleaner and more effective. The temperature gauge was in the same place as the old coolant on the gauge so all was good.

Share my Content