Hi Harry....welcome to the Forum
I would say it sounds like coolant being induced into combustion....e.g. Head Gasket failure.
You mentioned it smelt sweet, that would be the antifreeze content burning off.
Check for loss of coolant, and also run a combustion leak test (fluid changes colour if combustion gas is present in the coolant)
Let us know how you get on with it all
Cheers, Trevor