I pressure cleaned rad from inside to out a few days ago. The cheapy rad cap I bought from Azone had a slow leak (released pressure at 20 psi but would fall back to 17/18 psi and slowly leaked) so I found a MB dealer with MB one for 15 bucks and exchanged it (it held pressure at 20 psi). Put MB rad cap in and car tested and took longer to get hot no red line but close only at stop and go driving (high speed it was just above 100c mark). Radiator was too cool in center for as hot as car got... It's all pointing to water pump or radiator... not sure how to check water pump???? without removing it... Is there a way to inspect impeller without removing it??? Maybe removing thermostat or upper hose and using a dental mirror???
Thanks, Derf