Firstly, 36MPG average in a 300TD is v.good. Better than most I have met.
( Approx 475 mile tank range) and a lot depends on type of journeys and your right foot.
Personally, if i get 400miles out of a tank I am v.pleased ( 30Mpg).
But, I mostly drive in town not long runs.
Currently, my "cat" is still rattling - Has done for 2 yrs - no probs with MOT's.
I cant see how a new cat would reduce MPG by 6MPG (17%) - But it might.
Gutting the cat is also something I am considering.
Previous posts on this site and others have suggested that a Stainless steel
exhaust which would bypass the cat would free up more power and give more MPG.
According to previous posts, you will not have to swap back for MOT's,
as the presence or not of a CAT will not cause an MOT failure.
( As long as you do not touch lambada sensor further up pipe I am told )
If are able to gut your cat, then swap easily then why not give it a try.
Look forward to your feedback on this one.
Good luck.
Mike.
