Thanks Rayaans. Did this early today as coolant reservoir was almost empty. No signs of any leaks or water loss after short drive to reach normal engine temps, smell was evident. Gave in and drove to Lexus who could not find any problem at all they suggested I may have picked something up off the road which had stuck to the exhaust creating the smell, I asked why had the coolant dropped then and they suggested an air block. I must admit I have lost a little confidence in Lexus service which is a shame as I have owned several Lexus cars over the years. Any way back home and coolant level seems to be normal. Strange. I will check tomorrow. Thanks again