Oil or Temp??

[atif]

I recently got this 92 300D 2.5 Turbo with low mileage, it seems the car has been stored/parked mostly in the previous years, it had only 62000 miles when I got it. As I started driving it daily, I noticed this sewing machine like noise that would start in the engine after driving for a while as the engine warmed up.

I found it was the hydraulic lifters making this noise so I had them checked out, the mechanic found all the lifters had collapsed. I had all 10 lifters replaced, put new synthetic mobil 1 5W30 oil in it, noise reduced but would still come up when the engine warmed up e.g. a good 45 minute run on the freeway would bring the sewing machine noise back.

I researched a bit more and found out that it could be due to blocked oil passages and lifters not getting enough oil so after driving for about another 1000 miles these are the things I did:

Engine flushed with Liqui Moly engine flush and also found out about this product called AUTO RX Auto-Rx Engine Cleaner so after flushing...

Drained the oil and used Quaker-State non synthetic 20W50 with a bottle of auto-rx and I'm supposed to drain this oil in a months time and use non synthetic for another month [cleaning and rinsing process with auto-rx]

My question is which grade would be the best oil to use I have seen people use all kinds of oils and yet their 300Ds do not have noisy lifters..

Maybe my engine is running hot/very hot and monkeying with the oil viscosity as a result.

Freeway driving on hot summer day keeps my temp close to 90 C but stop and go/rush hour traffic and if the A/C is on it raises to 110 C and this is when the lifter noise comes back.....

I know its a little soon, I should let auto-rx work for at least a few weeks but just curious if anyone else out there is or has experienced something similar..yes I know these engines are noisy but what I'm going through is not on a friends 300D 2.5 Turbo i.e. identical as mine and his has over 250,000 miles and is quiter than mine!

Your input is appreciated.

Atif