I realize this question may be off topic for this thread, especially for the SuperChip distributor (Mike) but I figure with all the high performance testing they do they may be able to give me some input or insight to my question.

My question pertains to differential gear oil for limited slip as well as transmission fluid ATF for the manual transmission. I have read many post about different brands from Mobile One, Royal Purple, Amsoil all of which to be the most commonly brought up names.

My differential calls for 75W-140 full synthetic with 4oz of friction modifier. Amsoil states that theirs already has the friction modifier in it but I am not sure about Royal Purple or Mobile One. Amsoil sounds a bit pricey to me compared to Royal Purple and Mobile One.

Mike, if its possible, could you give me some of your thoughts or personal recommendation as to what you feel would be the best fluids and lubes to use as far as the manual transmission and differential go. Also, I don’t know if the Royal purple or Mobile One come with friction modifiers in them already, but if they do would you recommend using more (4oz recommendation from Ford) along with what ever may be in the other brands that say they already have it or not?

I apologize for an off topic question but after I got to thinking about it I thought who better to ask then someone that does a lot of high performance testing on the F150.

Thank you for your assistance.

Truck specs- 01, 4.2, manual, 3.55LS

 

Hi 01 XLT Sport,

We recomend using the Ford friction modifer *in addition* to whatever synthetic lubricant you use.

Mobil 1 is fine, they do use a fully synthetic base stock as of a few years ago, and their distribution makes them much easier to find on the shelf, so you don't need to spend the ultra-high bucks for Amsoil (excellent lubricant!) or Royal Purple (also excellent).

For years, most of the synthetics didn't advertise having a specific additive that they called a friction modifier, and some brands claimed that because they were synthetic, no additional friction modifier was necessary. In all candor I can't tell you exactly which lubricants do and do not have a specific "friction modifier" these days, as we ignore that and use Ford's friction modifier regardless, it's great stuff.

In general, we use Mobil 1 lubricants here at Performance in all our vehicles.

Good luck!

 

Mike,

Thank you for your reply. I have another question for you or anyone that would like to answer.

I wanted to go with Mobile 1 but I could not find any 75W-140 anywhere only 75W-90. So since it is required or recommended by Ford to use the 75W-140 I bought some Royal Purple on-line. ($7.36 a qt) the Max synthetic ATF was ($6.99 a qt)

I asked them if it had friction modifier in it, and if so would I need to add any. They e-mailed me back and said the Royal Purple already has the friction modifier in it and there is no need to add any.

I respect your reply Mike and the fact that you said to add the modifier regardless. My question is if I do add the 4oz along with what ever the Royal Purple has in it will there be any ill effects? To frame the question another way, will having more then just the 4oz that I would add from Ford harm it at all. I kind of look at it like they say the coolant should be 50/50 water and coolant, and if you say had a mixture of 60/40, 70/30 then you would actually start effecting how the cooling operates and would end up running hotter with more coolant then water.

I know to some this may seem like kind of a dumb question but I have recently decided to start doing as much as my own maintance as I can including changing the rear-end lube every 30,000 miles. So bare with me as I try to learn this and get some insight. This site is one of the greatest things I have found in many years and I cant believe how many knowledgable people are on here.

Thanks for your help...

 

Hi 01,

Ok good, if you couldn't get the Mobil 1 in the weight called for, it was a good move to go with the other synthetic, that's fine. We found the same thing here locally last time out if memory serves, & I think we just used Amsoil, it's been a while & I just don't remember off the top of my head right now. It's rare for us to even keep a vehicle long enough to need to change the differential fluid at all.

In general, no, you're not going to hurt anything by adding the Ford friction modifier to your synthetic differential lubricant. You may want to talk directly with Royal Purple's people about that just to get their take direclty, as I'm not qualified to answer for them, of course. I can tell you what *we* do, but I can't tell you what Royal Purple is going to say, in other words. No doubt you'll get the "none needed" spiel, that's perfectly normal from any synthetic lubricant manufacturer. We use the Ford friction modifier anyway, regardless of what lubricant goes in the differential.

Good luck!

 

Thanks alot Mike for you replies and helping me out. For you guys this is probabely basic 101 stuff. For guys like me that don't really mess around with it much I tend to ask alot of questions before jumping into something.

Even though Royal Purple told me through e-mail that the modifier was not needed I am going to go ahead and add it anyway to be on the safe side, and plus hearing it from someone as yourself with experence.

I would have just asked Ford but I am sure they would have said to add it regardless, a few more bucks in their pocket. That's the other nice thing about this web site and people as yourself. I can ask a question and not worry about someone giving me an answer just to sale their product to me.

Again, thank you very much for your help.

 

Hi 01,

Yep, that's what they usually say, and they aren't lying aobut that by the way, they all say it and feel that it's true of course. And it should be, with any full synthetic. But for me, I'll always use the Ford friction modifier in any Ford limited-slip differential, it give me piece of mind, and I couldn't care less about the few extra bucks.