back pressure in expansion tank

[shaf]

Hi All

Please can you help, I was driving my car with out any problems when i heard a noise and then the car stopped investigated that the water pump leaked and now it has been replaced. The pump is all sealed and no leaks, in this process i removed all coolant pipes and radiator after completing the job the car is giving back pressure and the water is coming out of the over flow in the expansion tank> Has my head Gasket gone?

My vehicle is 1971 280 sl pagoda

[rmmchl]

Maybe  there was too much coolant?-It's really easy to overfill.

[Benz Dr.]

You have air trapped in the block or somewhere it can't escape. I've seen this several times and usually on 280SL's.
Make sure you have your thermostat installed correctly.

[shaf]

The thermostat has been removed and does the same thing after 20 mints of running. How do i get rid of the trapped Air?

[mbzse]

The thermostat has been removed and does the same thing after 20 mints of running. How do i get rid of the trapped Air?

One useful method is to park the car on an incline, nose up. The trapped air then tends to collect under the thermostat, and then escape
via the little vent hole on the thermostat circumference.
/Hans  in Sweden

.

[rutger kohler]

I also had this problem and used a trick a radiator repair guy showed me.  I got a 300 ml plastic water bottle and cut the bottom out of it.  If you wind anough pfte thread tape round the thread where the cap screws on it will make a water tight seal in the inner  radiator cap hole  (with the water bottle upside down). I filled the water bottle up to about 30mm below the "top" and got someone to start the engine and let it idle  with me holding the bottle steady. When the engine warmed up there was an almighty burp and the air came out, and the water ran into the radiator.   I had to put a whole lot more water in too as a lot of air came out.  This fixed the problem for me, it seems this small increase in static head pressure is just enough to displace the trapped water.

[rutger kohler]

I just signed off and realised I said Radiator cap, should have said expansion cap.

cheers

Rutger K

[Benz Dr.]

A '71 280SL should have a 100 degree C thermo switch in the thermostat housing. Loosten it up a bit and the air should escape that's trapped behind the thermostat.