Tips & Tricks: Bleeding the cooling system

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Bleeding the cooling system on an R16 correctly is very important, and if it isn't done right there is a big risk of overheating the engine.

The design of the cooling system, with everything in the "wrong" order with the heater being the highest point and the radiator being the lowest, must be bled carefully. On most cars the radiator is the highest point, and since air rises these systems normally don't require bleeding, it bleeds automatically when the air travels to the radiator.

To bleed the cooling system you have to pressurize it. With this simple tool, made up by an old radiator cap with a pipe soldered/welded on it, a hose and a funnel, it's made easy. Just hook it up on the radiator and fill cooling liquid in the funnel!

Another way to get pressure is to run the engine, but there will be a very limited pressure to bleed from during each warmup, so it is a very time consuming method since you will have to allow the engine to cool down between bleeding.

Here is the tool at work.
Normally I hang it on one of the hood locks with a piece of string, but obviously this is not possible right now so I hanged from a hook in the garage ceiling.

If the level in the expansion bottle rises when the bleeding tool is connected you have a problem with the bottle cap either being defective or the cap gasket is not sealing properly.

For those of you who wonder what the grey, square box to right of the expansion bottle is, I can tell you that it is an electrical engine heater. Useful during cold Scandinavian winters...

With the cooling system pressurized start with bleeding the cylinder head with the screw marked 1 on top of the water pump. Bleeding is done by opening the screw to let the air out, and then closing it when water comes out. During bleeding you will probably have to fill up the funnel every now and then

The bleeding screw marked 2 is only present on older cars, and if you want to bleed the carburettor heating circuit on a car without this you will have to disconnect the hose from the water pump, put your thumb on the pipe, hold the hose up, wait for all air to come out, then quickly connect it again. Just remember to get your thumb away from the pipe first. This will probably require a helping hand, since somebody has to fill the funnel at the same time...

Finally you should bleed the heater matrix. This is done with bleeding screw marked 3, at the end of a short hose coming out of the firewall next to the air intake.
From this bleeding screw you may get some water first, before the air, so let the water run for half a minute or so.
On R16s from 65 and 66 the bleeding screw for the heater matrix is instead located on the hose leading from the heater (visible just below bleeding screw 3). If you have a car like this you should loosen the hose from fastening bracket to the left and hold the bleeding screw as high as possible while bleeding.

Start the engine and let the water circulate for a few minutes to collect any remaining air present in the system, and then repeat the bleeding process.

Magnus Bjelk (

Last revision 2002-12-18