Flushing the cooling system and replacing the radiator of my Renault 18

During itโ€™s winter sleep I noticed some fluid on ground beneath the front of my Renault 18. Turned out the radiator was leaking. I had also noticed the coolant was pretty dirty. So it was clearly time for some serious TLC for the cooling system. Last week I replaced the old radiator and some other components and thoroughly flushed the system.

Last look at the 39 year old radiator before removing it.

Removing the radiator

I started by draining the system and removing the radiator. This is pretty straight forward.

Without the radiator

Flushing the cooling system

To flush the system I removed the thermostat from the top radiator hose. After that I shoved a garden hose into the radiator hoses and flushed the system both ways several times. Also I used this procedure on the hoses of the cabin heater. 

The water coming from the cooling system was pretty filthy on the first runs. In the image below you can see the coolant that came from the engine and the first 15 liters of water that went through the system. After that the water became clearer and I dared to dump the rest in the sewer. In all I must have ran at least 50 liters through the system.

Flushing the cooling system
coolant and the first 15 liters of flush water
Gunk inside the expansion bottle

The expansion bottle also had a lot of gunk in it. It seems to be mostly rust. Just some water and a thorough shake dissolves most of the gunk. After that I used a bottle brush to remove the last remnants of dirty deposit, leaving the bottle looking (almost) new. 

Than it was time to replace the old thermostat and place the fan and thermo sensor on the new radiator and put everything in place, using fresh clamps.

Old thermostat in the top hose
Old and new side by side
new sensor and clamps
shiny new parts

Filling and bleeding the system

Then it was time to fill and bleed the system. I used Renault Glaceol RX Type D to fill the system. With the expansion bottle attached to a wire to keep it above all components I warmed the engine and opened the 3 bleeding screws reguarly to let the aur escape from the system. It was nice to actually see and understand what was happening. The temperature indicator rose nicely. After a while the top hose started to warm and the temperature indicator droped a little, indicating the system had reached 86 degrees celsius and the thermostat was opening. At 92 degrees celsius the fan kicked in and switched on and off regularly.

One happy engine. At the end of the video you can hear my sigh of relief ๐Ÿ™‚

Some water stays behind in the engine

It is good to know that when you flush the cooling system this way, some water stays behind in the system. In my case it’s about 1 liter. It seems there is a screw on the cylinder block to remove the last coolant or water from the engine, but where it is, remains an unsolved mystery. I added 5 liters of coolant. So there now is about 16.7 % of water mixed with the coolant.

Don’t loose the bleeder screws

When bleeding the system, the bleeder screw on the cabin heater hose slipped from my fingers and rolled under the unit. The only way to get it from under there is to remove the unit. Aghhhhhh!!!!

So instead I found a temporary solution: A nice white plastic M8 screw with a rubber ring placed around the top. It does the job. Someday in the future I will replace it with the screw from my donor Renault 18.

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