How to get air out of cooling system on 94 mercedes E320

  • 1994 MERCEDES BENZ 320E
  • 84,000 MILES

I put on a new waterpump and thermostat, now coolant is not circulating to heater core. Someone told me it could have airlock. Thanks!

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have the same problem?
Saturday, November 19th, 2011 AT 8:56 PM

2 Replies


You sure you didn't put thermostat in backwards?

Check if it has an airbleed screw-if so open it up and remove the resevoir bottle cap, now put coolant in it untill it comes out of the airbleed screw then close the screw. Now start it up and put heater at high-let it idle till it comes up to temperature-keep an eye on the resevoir keep it fill at all times, once the upper hose gets too hot-stop you're done

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Saturday, November 19th, 2011 AT 9:09 PM
  • 3,440 POSTS

Whenever filling an empty or near empty system, there is a few things you can do to minimize air pockets. It is harder sometimes to get air pockets out of already filled systems. Try the following;

Always wait for the car to cool off as pressure builds up and removing the radiator cap under pressure can cause hot coolant to escape rapidly and burn you.

You can check for pressue by grabbing the upper radiator hose and feeling for resitance. You can grab it when it is hot to see what it feels like when there is pressure in the system. When it is cooled off and the pressure has dropped, you should be able to collapse the radiator hose till the sides touch.

Turn the heater on in the car all the way hot.

Look for a, "Bleed" screw on the cooling system. They are often near the thermostat or upper radiator neck as this is the highest point in the system.

Remove the radiator cap and get a funnel and some anti-freeze that is mixed at a ratio of 50/50 with water. Fill the system while grabbing and letting go of the upper radiator hose usntil full.

Start the car. If there is a bleed screw find a closed end wrench to fit it.

Continue to fill the radiator and wait for it to reach operating temerature. You should see the level of coolant drop when this happens as the flow of coolant is not impeded by the closed thermostat.

Continue to fill until it is topped off and then fill the reserviour to the low level.

It is a good idea to lossen the bleed screw if so equipped and tighten it just snug so it can be loosened slowly.

Put the radiator cap on and wait for pressure to build in the system which should happen quickly.

If you have a bleed screw, then open it, slowly loosen it as it can be dangerous to open it too fast under pressure and be careful of stream. Repeat this until a steady stream comes out.

Allow the vehicle to cool and repeat the process. Do so until the level of the radiator and reserviour don't change.

Drive the car for a few minutes and see if the heater expels hot air. If not, allow the car to cool, turn the heater temperature to 1/4 or less from the coldes setting.

Repeat process. Do so and every time keep turning the heat to a cooler setting.

You may have to drive the car normally for a while but within 50 miles or so, the air should work itself out.

If it does not, then you may have a leaking head gasket. Have a Cooling System Pressure and leakdown Test done. This will indicate the presence of a leak.

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Saturday, November 19th, 2011 AT 9:23 PM

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