Can you add a 20/50 oil to 4 qts. of 10/40 when changing the oil? 225k miles. on 1994 Ford Thunderbird

A mechanic said he adds 1 qt. of 20/50 to 10/40 when he changes oil. I asked about the "no Zink" in the new oil not good for older engines. I've used 10/40 for many years, now. Do you think this is a good idea?

Asked by for the 1994 Ford Thunderbird
try lucas oil additive,its better than 20/50
Good stuff!!
I have dixie chopper , thats required , thats what i use
The lucas 15 40 diesel oil...awesome stuff..
1 more answer
Yeah thats good , everybody has a diff opinion about oil
I personally put 20/50 in everything i own , rite down to zero - turns
Never had problem