delvac 1 vs m1 5w30, recommendation

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Feb 15, 2004
a while back i bought a 4 gallon case of d1 5w40, but having a few second thoughts about using it now in one of my cars.. engine is the old 2.5 'iron duke' gm motor - old school pushrod design, gear driven cam too (no chain, no belt). all metal gears were used in the rebuild. (factory is one fiber/one metal). it's regularly driven to redline rpm (ok, so that's only 4500rpm, it doesn't pull past that) and summer temps can get to 110*F and maybe higher. typical commute is an hour at 3000rpm. definately sees more 'abuse' than your average car. motor has 40k miles on it, all with m1 5w30, 5000mi intervals. no UOA's. lowest PSI i see on a hot summer day at idle is about 30psi. any chance that the D1 5w40 is unnecessarily thick and not to my advantage to use? any other comments?
It's got a lot of miles left in it don't worry. I've had several "Iron Dukes", all over 150,000. My current one was not taken care of, and it still runs fine at 187,000. As long as you don't rev them too much(keep it under 4000), it will be fine with just about any oil. I don't think a thicker oil is really neccesary. I'm currently running Havoline 10w30 in summer and 5w30 in winter, before that I ran Mobil Drive clean. I'd stick with the M1 since it has more FM. I considered running a little D1 to see if it would quiet the engine down a little, but I've been having second thoughts. -T
Yeah, quieting the engine is one of the reasons I've considered running the D1 as well. that ghastly 2.5 valvetrain noise is amplified even more with the use of all metal timing gears, like I have (at least they won't break). The motor went to 150k before the rebuild, and was rebuilt without reason (had to have the motor out, did a clutch job...might as well do motor too). so I know it's got plenty of miles left. as for not revving it... [SPAZ!] not going to happen. [Smile] 4500rpm and I regularly meet, that's about the best shift point in terms of achieved performance. some might call it abuse, but eh..thats how i drive it, got to be honest with myself.
I run D5W40, but in a Toyota V6 3.4L which is a lot different than yours. But, it idles so smooth that I cannot tell it's even running when sitting in the vehicle! No noise or vibration! It's pretty amazing. I use Redline Fuel Cleaner every so often which helps, as well.
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