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+--- Thread: HIGH ZINC MOTOR OIL INSTEAD OF GL-4 GEAR LUBE (/showthread.php?tid=10545)
HIGH ZINC MOTOR OIL INSTEAD OF GL-4 GEAR LUBE - harshaanbop - 03-19-2026
Hey guys, so I know, this topic has been brought up all the time and is never ending, but I did my own research as well and haven't seem to find anyone say the same in this forum, so instead of adding that gallon of gear lube every oil change to our isx's, wouldn't it make more sense to use a gallon of {aftermarket branded} 10w40 high zinc motor oil instead? Because thinking about it, minus the thickness that gear lube provides to regular 15w40 motor oil sure, It just makes more sense to use a gallon of 10w40 instead. The high zinc content is there for our cams, the viscosity shockingly stays almost the same throughout most temperatures, and has the Cummins approvals, which deleted and older non-emissions engines being fine with it. Just to note, I am NOT sponsored or promoting in any way. Just a regular owner op like many on this forum. I just want to hear opinions about this here so I can get corrected where I'm wrong, and what to do and not to do, plus this can help others thinking the same way. Again, Thanks to all everyone does here on this forum I'm looking forward to those answers about this!
RE: HIGH ZINC MOTOR OIL INSTEAD OF GL-4 GEAR LUBE - Nostalgic - Yesterday
Well, I've actually tried what you're describing - kind of. I am/was a dealer and since closing automotive repair, found myself with a lot of lines that are just sitting on the shelf. I have the high zinc Z-rod stuff, and added a gallon or so to my oil change. It did nothing to the numbers for zinc since it's still diluted by 10 gallons of rotella. Maybe a point here or there, but no meaningful additive change outside of normal batch variances. The additive pack for a gallon of gear oil DOES show up on a UOA. Gear oil doesn't really change the viscosity much overall, but it's additive pack and film protection DO.
Ironic, the GL4 I was using became hard to find and expensive, so I quit adding a gallon. Not that I'm against it - in fact UOA reports support Rawze's theory and opinion on its use.
I also experimented with zinc additive. Of course even dumping 6-8 bottles in didn't sway zinc's ppm on a used oil sample.
RE: HIGH ZINC MOTOR OIL INSTEAD OF GL-4 GEAR LUBE - harshaanbop - Yesterday
Obviously for the price, it seems overkill to me. For the price to benefit comparison, I'll stick with gear lube, at least my oil samples are coming out fine everytime with the GL-4.
RE: HIGH ZINC MOTOR OIL INSTEAD OF GL-4 GEAR LUBE - Rawze - Yesterday
(03-19-2026 )harshaanbop Wrote: Hey guys, so I know, this topic has been brought up all the time and is never ending, but I did my own research as well and haven't seem to find anyone say the same in this forum, so instead of adding that gallon of gear lube every oil change to our isx's, wouldn't it make more sense to use a gallon of {aftermarket branded} 10w40 high zinc motor oil instead? Because thinking about it, minus the thickness that gear lube provides to regular 15w40 motor oil sure, It just makes more sense to use a gallon of 10w40 instead. The high zinc content is there for our cams, the viscosity shockingly stays almost the same throughout most temperatures, and has the Cummins approvals, which deleted and older non-emissions engines being fine with it. Just to note, I am NOT sponsored or promoting in any way. Just a regular owner op like many on this forum. I just want to hear opinions about this here so I can get corrected where I'm wrong, and what to do and not to do, plus this can help others thinking the same way. Again, Thanks to all everyone does here on this forum I'm looking forward to those answers about this!
Sounds like the regurgitated typical {name removed} salesman's brainwashing crap to me.
FIRST AND FOREMOST!!!!... more, more, more zinc (zddp), above a set level ppm is actually MORE harmful to an engine. The optimum on older oils is between 1250- 1440 ppm .. and this is considering that the oil does NOT have other replacement additives to make up for less zinc.
Regular ole' Delo-branded oils get pretty close to this as is.. so if you want to run the 'zinc' experiments on your engine, simply use Delo-400 oil.
NEXT:... STOP OBSESSING ABOUT YOUR OIL !!!!!!!--- ITS F%$#KING POINTLESS ON AN OTHERWISE WELL CARED FOR ENGINE!.
IT IS ALWAYS A NON-LUBRICATED COMPONENT THAT FAILS OR WEARS OUT AND NO SUPER-DUPER EXTREME PROTECTION FRICTION-LESS OIL CAN STOP THIS!!!!!!...
Here is more info on this: https://rawze.com/forums/showthread.php?tid=5669&pid=48724#pid48724
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