Few posts, long time lurking on this site. 97 with a 5.4 eng. Strong smell of coolant when you are sitting at idle or when you shut the truck down. I recently replaced the heater core but the smell was there before and afte the core change. I looked with a mirror at the line that runs under the intake manifold and I do not see any fluid or rust there that would indicate a leak. I have also checked the hoses running to the heater core but no leaks there either. Someone mentioned in one post of having a crack in the resevoir tank but I have not checked for that either, no visible leaks and no fluid on the ground. I'm stumped.....

 

I have a 98 with the 4.6 motor and was having the same issues turned out to be one of the freeze plugs and a small leak on the drivers side head gasket. Best to have it checked out.