First lets get rid of the myth that by raising one end of the car it helps release the trapped air. Raising the front would actually make the problem worse and when raising the rear, you would have to get the radiator virtually flat to get the trapped air to flow out naturally, meaning the car would have to be almost upright on its nose! Obviously that is not possible. Second the bleed screw in the hose from the thermostat will only release the air trapped in the engine, NOT the radiator, and only after the thermostat has opened really.
Since the top of the radiator is much higher than the pipes that run under the car to the engine, if you pour new coolant into the header tank in the engine compartment, you will trap air in the radiator, and have difficulty removing it without following the correct procedure. Any air locks in the cooling system can cause overheating in the engine, and overheating will cause a blown head gasket at best, and a cracked cylinder head and/or seized engine at worst, so this is definitely to be avoided!
Correct procedure (always have the heater control set to full hot when refilling a cooling system and running it up afterwards): There is a small hose that joins the top of the radiator to the header tank, specifically fitted to bleed the air from the radiator, and if you use this to draw the air out of the radiator (blanking off the header tank connection whilst you carry this out) you will get rid of the largest amount of trapped air straight away. You really need a vacuum pump to pull the air out, but you could use a long piece of clear pipe (and use your mouth to suck the air out) watching for the first signs of coolant to appear in this hose before it reaches your mouth! Once there is no more air coming out of this hose, you can refit it to the header tank. There should be a bleed screw fitted into the hose connected to the thermostat housing, and you should leave this open when initially filling but then close it whilst warming the engine up after filling the system and bleeding the radiator. Once the thermostat is open you should use this to get rid of the remaining air from the engine. Be careful as the initial steam is extremely hot and the fluid will also be very hot. When it is 'bubble free' close it off. Now give the car a run, taking some spare pre-mixed coolant with you. (Coolant should be one third anti-freeze to two thirds water). Keep a careful eye on the temperature gauge and if the temperature rises above around 95 degrees, and the fan has not cut in, stop, switch off, look for leaks and check fluid level through the translucent header tank. If necessary let it cool and top up. At the end of the run, let the engine idle and check the cooling fan cuts in correctly. Again if the temperature rises above the cut-in point (approximately 95 degrees) and the fan has not started, switch off and find out why. Always be aware you are working with a hot pressurised system. This means that as you release the pressure the coolant will expand and boil since the pressure was suppressing the boiling point. N.B. If there is much air in the radiator the fan switch, which is near the top of the radiator where the air will also be, cannot work and trigger the cooling fan as it will not be reading the coolant temperature.
NEVER LET THE COOLING SYSTEM TEMPERATURE RISE ABOVE 100 DEGREES.
See the technical articles section for my full article of the cooling system. Since the radiator is some distance forward of the engine, and it takes time for the coolant to reach it, plus there will be some cooling effects owing to the variable outside temperature and the cooling flow under the car, the point when the radiator fan switch reaches its cut-in point will be at a different (slightly lower) temperature to that of coolant in the engine. Ideally it should be the engine coolant temperature that triggers the radiator fan, just as with modern cars. There is a way to fit an engine fan switch, but it requires a little modification around the thermostat housing. There is no drilling or other difficult things, just some moving of items and so it is a relatively easy modification which will enhance the reliability of the fan switching.
Please note, if you have a 1981 Murena with the deep header tank, this may not have any 'Mini' and 'Maxi' mouldings in the side. If you have one of those, the correct maximum level is just above the wire clips that hold the tank in the engine compartment; when the system is fully cold.
A second improvement which I would strongly recommend is fitting a coolant level sensor, so you get an immediate warning of any coolant loss long before this will cause any engine damage. This level sensor can be coupled to the level sensor system already wired into the Murena, so the connections are quite simple and don't involve any major re-wiring. See my technical article (updated May '24) if you wish to carry out these improvements, which will make your Murena 2.2 more reliable, especially if you use it regularly.) I can provide all the details necessary and maybe the parts required, if you contact me.
Note: It is common that after any work done, this is the most likely time for problems, since things have been disturbed. So always keep this in mind and watch things carefully until you are sure they have settled down and there are no further problems.
I have found out that there were some faulty Murena 2.2 water pumps made some years ago, which had an incorrect impeller fitted. These incorrect impellers caused a lack of coolant circulation at idle. Since the engine would be idling whilst sitting stationary in traffic, this lack of circulation would mean that although the radiator and fan were capable of cooling the system, as the hot coolant never reached the radiator, there was no way it could know it was getting too hot, nor attempt to cool it! If you speed the engine up to say 1,500 rpm rather than let it idle, the additional revs started the circulation, and the system would start to work as intended. However, you should never have to increase the idle to get the system to cool, so if you find you do have to do this, you probably have one of those faulty pumps.
Some of these pumps with incorrect impellers had a smaller diameter pulley fitted, which caused the pump to spin faster and these were probably made and fitted to compensate for the lack of circulation at idle, without understanding why the problem had arisen in the first place. As the impeller vanes also had incorrect edge angles and could never work efficiently, they probably never circulated the coolant properly even at higher revs and would not have been as good as a correct pump in any situation, but whilst moving on the road at normal speeds this probably never showed up because there was more than sufficient cooling within the system at those speeds. However, at the top engine revs, the faster spinning water pump might have had some cavitation problems. Also the smaller pulley probably required a shorter vee-belt than normal. My advice if you have one of these pumps with a smaller pulley (which you could easily measure and maybe see) and an incorrect impeller (which you could not see without removing the pump) would be to change it for a proper pump, or at least contact me.
Back to top
