...Another reason for pressurised radiator top hose is a PARTIALLY BLOCKED RADIATOR.
Check out this thread: -
http://www.benzworld.org/forums/r129-sl-class/2475825-hot-running-v8-conundrum-11.html
Alan67 had a similar problem. His mechanic replaced the radiator in an attempt to cure an overheating problem, but unfortunately he did not flush the cooling system first. He also used antifreeze which was not compatible with the antifreeze already in the system, which led to a reaction between the two antifreezes (IAT and OAT), which caused the coolant to gel, creating a partial blockage in the brand new radiator.
At the end of Alan67's thread is a video of him testing the new rad, confirming it was blocked. He flushed the system and replaced the radiator again, which cured the overheating.
This tale is a credit to Alan's tenacity and sense of altruism. He documented everything step by step and followed it through to the end, so that the rest of us at Benzworld could benefit from his experience.
Alan67, if you're out there, you deserve a reward and I take my hat off to you. <img src="http://www.benzworld.org/forums/images/smilies/thumbsup.gif" border="0" alt="" title="thumbsup" class="inlineimg" />
Benzworld working at its best!
Hope this helps <img src="http://www.benzworld.org/forums/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />