I have always used Royal Purple motor oil in my previous vehicles. I have read that RP 5W40 is a good replacement for the Mobil1 0W40, however the only 40 grade oil my local Royal Purple supplier carries is 10W40, which I use in my '68 440 Road Runner. Can I use the 10W40 in my '06 SRT8 also or will this be too thick on startup in cold New York State winters? I am all stock right now except for the airbox snorkel mod and drop-in K&N filter. Future mods will be bolt-on only (180 deg thermostat, CAI, Predator canned 93 oct tune, cat-back, ported intake manifold, CMR dynotune). If the RP 10W40 is too risky with the 6.1 Hemi, I will just stick with the stock grade Mobil 1. Thanks in advance....

If you like Royal Purple that much, you can order the RP 0W40 online. It is a little more expensive (about $10/quart) compared to the Mobil 1 at about $7/quart.

Depending where you live... If you have no worries of -20F or lower temps you can use RP 5W40 and its about $7 a quart online as opposed to 0W40 for $10
http://i165.photobucket.com/albums/u51/JDesautels/oil.jpg

i have always used mobil 1 in my cars and was really glad when they put mobil 1 in our cars in the factory. i think it is god to stay with the stock oil since its not the usual the cheap pennsoil stuff that comes in most cars from the factory

Mobil 1 FTW, no complaints no issues from anyone ive heard, no engine wear, sludge nada, its great and especially when its $7/quart vs. the Name you pay for for Royal Purple ;) jmho, gl

I would stick with the mobil 1 0w40 :p

Try 15W50 in the summer.

I've been using royal purple now for 3 years on all my rides and i haven't had any problems. when i first switched, i had an 07 m3 that always ran mobile 1 synth, i actually noticed a difference when goin to royal purple. it pulled smoother and stayed cleaner for a little while longer between oil changes.