Bought a 99 sl500 that needed some work. Looking much better but now the engine has a smell when warm that can best be described as cat urine. My mech has no clue. Anyone else exp this problem?

 

Hello - have you replaced the air filter and cabin filter as well? If not, I would start with those. Perhaps some rodents got in the car while it was sitting. You can also do a thorough engine cleaning - just google 'cleaning engine bay' and you'll get a lot of populated results.

 

check hood pad and the cabin filter on top of firewall . lift off rear hood seal and a couple screws in the housing toward the back and some pop clips up front. check for varmint nests all around the engine, especially around engine manifolds.