Knowledge Base

How to remove any air from the coolant system

How to remove air from your coolant system
by Martin Howell

If you have got air in your coolant system, you need to a) get it out, and b) find out what caused it.

Find out what caused it

Change the pressure cap (about 15 quid) and the plastic cap on the overflow bottle (about 12 quid, Mr T may need to order it).

Crawl around underneath the car to look for signs of water leaks, then run the engine and repeat the crawling around. Possible trouble spots are the radiator itself, the thermostat housing (casting pinholes or rust on the pipe), any rubber hose, any metal pipe carrying coolant, water pump seals.

Get it out

There are two bleed valves that matter, one on the radiator (top right as you look at the front of the car), you have to take off the plastic cover under the bonnet between the headlights. The other is on the heater, take out the spare wheel, remove the plastic cover behind it, the heater is the bit with the pipes right up just below the windscreen. Somewhere in the boot there should be two lengths of plastic pipe. These fit over the little pipe on the bleed valves, the other ends should be tied up as high as possible without kinking the pipes.

With the engine COLD, set the heater to 'hot' and open the bleed valve taps a couple of turns. You may get air come out. Pour new coolant into the pressure cap 'ole until its full, you should now have coolant in the bleed pipes at the front - if not, open the taps a bit more until you do. Top off the coolant and replace the pressure cap and tighten it to the first click ONLY. Tighten both bleed valve taps. Start the engine and let it idle until warm - about 5 minutes. Stop engine, carefully take off pressure cap, open the bleed valves again and top up. If it takes lots of coolant, close bleed valves, repeat the run engine business again. Do as often as required.

When finished, tighten the pressure cap down to the second click, take the car for a brisk run, then let it get stone cold before checking the level under the pressure cap, top it up as required. Check the level every day for a week or so and top up - if it takes more than a spoonful by the end of the week, you got a leak.

Standard health warning. DO NOT open the pressure cap when the engine is hot, or even warm (except if its turned down only to the first click as described above). The sudden release of pressure will cause the coolant to instantly boil, and it will erupt out of the hole and over your arm, face, genitals, and anything else in the way. You do NOT want that.

: Wed Feb 18, 2009 5:18 pm

Very helpful thought it was going to be a nightmare to do nice and easy after reading this [Applause]