My manual says 5.8.
The issue though is that the 2.5 has inadequate oil drainback. They did not provide adequate drainback holes from the head back to the pan. What happens, is that you can end up sucking air instead of oil into the oil pump with high revs on long sweeping right hand turns (like some freeway on ramps).
To partly resolve this, many keep the oil level a bit high. I use 6 quarts. Some here use as much as 6.5 quarts.
It is also best to avoid hard spirited driving on long sweeping right hand turns.
By the way, i don't think much of Lucas products. You would be better off just using 6 quarts of quality oil. There are worse snake oils, but there is no true benefit except that it made your wallet lighter.
Also, this engine prefers 5W30.
