From B Purcell website (
http://www.esatclear.ie/~bpurcell/318ismaintenance.html#bleedBleeding the coolant system
Time = 10 minutes Task=Easy
The engine and radiator are well designed to pretty much self bleed so this is not too difficult.
Remove the radiator cap.
Pour in a water/antifreeze solution (as required in your area) so that it reaches the level mark on the radiator.
Turn the interior heater/air con to full heat and turn the fan to its 1st position.
Start the engine.
Continue to slowly add coolant until it is ~2"/50mm above the level mark on the radiator. Keep the level there while the engine idles.
After about 5 minutes the top radiator hose should be getting hot as the thermostat opens. Once this is warm, loosen the bleed screw slightly until some air or coolant comes slowly out (~3-4 turns).
Bring the revs up a little and watch the bleed screw. As soon as pure coolant with no bubbles is coming out, tighten the screw with the revs still raised.
Check the coolant level and replace the radiator cap.
With fresh water, wash down the area around the front and side of the radiator to remove any antifreeze which may have come in contact with the paintwork.
After ~1-2 hours of use, release the bleed screw again, bring up the revs, check for bubbles coming out and check the coolant level again.
Regarding the T-stat, just get the one with the lower temp readings so it opens earlier. I live it hot weather and always use the t-stat.