Hi Mike.The Mercedes Forum do not know what couses the radiators to blow up(damageing the bonnets).I fitted new rad,and cap,+thermostat(the old statt was missing,perhaps because of overheating due to the viscous fan not working?) I took scanner readings and the only code that came up was 021idle speed cont in limp home mode.I cleaned the throttle housing and checked the wiring loom,idle speed was still 1400rpm. I turned my attention to the coolant temp sensor,the wiring has started to deteriorate but I do,nt think this is the problem. The fault with the idlespeed only started after the radiator blew up. I hope you can help with this one? Regards TONY.