air pocket in cooling system?

[davids]

This is why i am thinking of replaceing the heater core ,my heater core is not leaking, but twice now i have gotten a air pocket in my cooling system,where when the car is running it is pushing coolant out the overflow bottle.I disconnected the heater core and it seems to be fine.has any one ever heard of something like this before ? I hate to pull the heater core if I do not have to.

[Jonny B]

I searched the forum using "coolant" and searching in the topic line only. Here is one thread regarding the air pocket in the cooling system
http://www.sl113.org/forums/index.php?topic=3851.0

[wwheeler]

I had temporary problems with air when I changed my coolant on my 111. It burped out the radiator (I don't have the seperate tank). It was as described before, air trapped in the WRD. In fact, the WRD would never "warm up" because there was air trapped and wouldn't allow the thermostat to feel the real temperature. As suggested, I would remove the top hose and fill the coolant system until coolant comes out the top of the WRD (use a catch pan!). Shouldn't have air then. 

[jaymanek]

I had to remove the bolt from the top of the thermostat housing to get the air out of my system after a head rebuild.

[DavidBrough]

I’ve had quite a lot of experience in refilling the cooling system as I had a long spate of issues with my car hopefully all now resolved.

Having had many an air lock and trying various different methods of filling many involving opening a hose joint and filling via a funnel from numerous different points I found the best way to be as follows:-

1.   Check all hoses are properly fitted and the system is fully sealed.
2.   Ensure you regularly check for leaks throughout the process.
3.   Set the heater leavers to hot.
4.   Slowly half fill the system via the header tank with your chosen coolant.
5.   Start the engine and allow to idle.
6.   Whilst idling continue to fill the system slowly until coolant just starts to appear in the bottom hose of the header tank (do not fill the tank) whilst checking the temp gauge to ensure the system doesn’t overheat (see later). Don’t fill too quickly or too slowly such that the engine reaches temperature before you’ve put enough coolant in. You can stop and start the engine as the temp starts to climb as the on off surge can help force any air out. Always ensure that the engine is running when you fill under this section.
7.   As the engine warms check that the WRD is also getting hot and if not follow the air lock instructions below.
8.   Once the thermostat starts to open and the radiator and WRD are fully hot switch off and allow to stand for a few minutes with the header tank still open.
9.   Half fill header tank fit the cap and give the car a run.
10.   Re check and top up to level after the car has had one full hot/cold cycle and you should be OK.

If you fill the system too quickly under 4 & 6 above then either the thermostat and or the WRD can become air locked.

If the thermostat doesn’t open at item 6 switch off the engine at normal temperature and individually pump the bottom and top hoses vigorously with your hand and the thermostat usually opens very quickly. You will know this immediately as the hose will warm up very quickly. If this doesn’t work straight away start and stop the engine a few times and try again. Make sure that the header tank is open at all times with the cap in a safe place and don’t let the engine overheat. You should also check that the WRD is warming up at this point as if not that will also have an air lock

If the thermostat process doesn’t also solve a WRD problem then you may well need to start again by draining the system into a bucket and filling it more slowly. If you get to this stage it’s always worth opening the WRD hose clamps starting the engine and gently letting the some water pump out by manipulating the hoses but do wear gloves at this point.

 If you take your take your time with steps 1 to 10 then you will usually have no problems at all as the open system and the action of the water pump forces the coolant round the engine and the air out.

[davids]

thx for all the help.

[Benz Dr.]

Some cars work easily and some push coolant all over the place. Filling while running produced mixed results for me. The engine will heat up very quickly while running and usuall faster than you expect. Once it gets too hot all you will have is steam coming out which is now your air lock.
Rads that fill from the header tank generally don't cause this problem. When mounting the thermostat make sure the bleed or vent ( if it has one ) is at the top so air can escape. We sometimes drill a small hole in the thermostat for this purpose. If you know the capacity of your cooling system start with plain water first and then add pure anti freeze later. If you have a gusher it won't make such a big mess all over the engine bay or shop floor.