| In all the years I've been a member of this forum and more specifically, an owner of a Z32, the question of what oil to use seems to come down to 10W-30 synthetic lubes. I've always been running Mobil 10W-30 since the beginning of ownership. At first glance under the hood, there is a gold OEM sticker that shows two primary weights to use - the number at the top being 10W-30. The Z32 is the second vehicle I've ever owned, and I still have my first vehicle, a 1990 Mazda B2200 pickup, which I've always run Castrol GTX 10W-30 in (for over 300,000 miles since purchase). Short story, I've always run 10W-30 in my "vehicles". :) I've been into countless VG30's over the past 10+ years and have seen a wide range of bearing conditions upon teardown. Early in my membership here on tt.net it was quite an achievement to have a Z32 pushing over 450RWHP but nowadays those numbers have more than doubled to be in that "club". Making these new levels of power are putting huge loads on the bearings and more importantly, the lube. The lube is what really supports these forces to keep the bearings from actually touching the rotating parts. Once the pistons have been upgraded, the next weakest link in the bottom end is the connecting rod bearings - this is the most common failure in the bottom end of these motors. After finishing the build of my current Z and having seen where the common failure point is in the bottom end, I vowed to inspect the rod bearings at 15K miles. I have and always will use OEM bearings - being able to accurately size and balance the tolerances throughout the rotating group using the various thicknesses that Nissan offers, not to mention all of the development they put into their babbit material (Kelmet), I just wouldn't do it any other way. After completing the build and final tuning, she put down some 540RWHP on pumpfuel and 690RWHP on racefuel. I never ran racefuel in the motor after that tuning session and put 93 octane through her at ~18psi daily, driving like I stole it, until 15K miles where she was sprawled out on the jacks for her examination. All of the upper rod bearings were showing copper substrate - pretty consistent across the board - ~15-20% of the total surface area showing copper just about dead center at the "top" of the bearing arc. There was no galling or scoring of the material and the crank journals were spotless. I replaced all of the bearings with new OEM bearings and continued to drive her just the same for another 15K miles. Once again, she was back in for another inspection. For all intents and purposes, the wear was identical. All of the upper bearings were showing copper, no galling or scoring, and the crank journals are spotless. New bearings, round three. Since that first go-around with the bearing inspection at 15K miles I wasn't going to change the approach and just let them go. It was apparent that with the amount of power/torque the engine is making, I wouldn't trust the rod bearings to go more than 20K miles before the tolerances are just too great to properly support the loads and then wipe out a bottom end, especially considering the 60+ hours I have in the millling of the crank to remove 8lbs, knife-edge, and balance. I will be coming up soon on the next inspection/bearing replacement. Going back to that sticker underneath the hood, if you look closer at the fine print at the bottom, you will see that they say 20W-40 or 20W-50 can be used if the ambient temperature is above 50F all season. Down here in Florida we rarely see days below that and right now we will see many more days at twice that temperature. At this point I am inclined to change out to 20W-50 and see how the bearings hold up over the next 15K miles. Higher weight oils have greater film strength, meaning they can handle greater loads and prevent bearing to journal contact in high power applications - less bearing fatigue and longer life. Granted, thicker oil will rob some additional power, but I would be willing to give that up even if only for additional assurance that I wont end up having to replace a crankshaft. Granted, running 10W30 and replacing the rod bearings every 15K miles is apparently working well - do you mess with something that works or? So, for you guys out there who have built setups pushing 500+ RWHP daily who drive their cars hard, how many rod bearing failures have you had and what weight oil have you been running? How many miles have you put on the engine? What kind of ambient temperatures do you run the car in?
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
|
08:40:57 06/21/10
