flat tappet recommendations

[bonnie john]

what is the lowest viscosity mineral oil that you would consider using in a '70s flat tappet V8 engine.

it is an australian engine. ambient temps range from about 10 degrees C in winter to about 40 degrees C in summer

so far my searches here have shown 20w50, 15w40 and 10w30 are used by members here

what advantages could i expect changing from a 20w50 to a lower viscosity oil. the vehicle is a holden (GM) ute running std cams and compression, but is on LPG/petrol IMPCO dual fuel

many thanx, johnny

 

[bruce381]

30wt
bruce

 

[Dr_No]

Take it from bruce

 

[Camu Mahubah]

What oil have you been running? Also how much does oil cost per quart or liter in Australia? What specs are on the bottle of the oil you have been using? Is it SM GF-4?

 

[junebug]

I have a 79 Dodge P.U. 2WD. 225 slant 6. I initially bought Rotella 15-40.( CJ-4 newest stuff) After reading many posts and charts from this site,I returned the dino Rotella and bought dino Castrol 20-50(SM rated),as it had higher zddp levels which is a necessary additive for flat tappet engines.Try to find an oil with higher levels of zinc and phosphorus. This seems to be getting more difficult.

 

[NCGuy68]

Go with a quality 15-40 SM rated. Better cold start-up protection. Another option is to use Valvoline 20-50 racing oil if available. It contains enough zinc for flat tappet motors.