Any synthetic 75W140 will work fine. RP is no better than any of them.

 

Glc---not to start anything here, but can you explain? I've watch a HORSEPOWER TV episode where they took a late model Camaro and did a dyno run to get a base. They then change the OIL, Transmission fluid, and rear Diff with ALL Royal Purple fluids. They then did Another dyno run where it showed they gained like 12 or 15 HP just by changing the fluids!!!!!!

I know there are a lot of snake oils out there. But RP seems to be more slippery than other brands. It makes common sense to me that if an oil is more slippery than another it is reducing friction and causing the engine to work less hard, resulting in more power and better mileage. I want the better mileage part. Granted I know it not going to get me to 20mpgs in city driving, but I'm sure it can help with either .5mpg-1mpg. Over time it can pay for itself.

If you have any contradicting information, i'd like to review it.

Again, this post is made with respect and I'm not trying to start a thread flame war. ---Just trying to learn and get all the facts I can---DirtySCREW

 

RP is not the only synthetic lubricant manufacturer. There is very little difference between the various brands. I'd bet that they would have had very similar results if they had used, say, Amsoil products. However, there IS a difference in "synthetic" motor oils - some use GP 3 petroleum base stocks, and some use PAO. The PAO's are a bit more "slippery". RP's motor oil is a PAO, as is most (but not all) Amsoil.

Now, when it comes to ATF - we have a couple professional tranny guys here, and they both do NOT recommend the use of RP in a 4R70W. However, they do endorse Amsoil. Now, to add more to this, a member just posted that when he changed his tranny over to Amsoil, his temps rose instead of dropped.

Bottom line? Ford specifies a full synthetic 75W140 gear oil for the rear in your truck. It doesn't really matter what brand you use as long as it meets the specs, and I doubt that you would notice much difference at all. Also note that they used a Camaro, which specifies 75W90, not 75W140.

 

The fuel filter might be dirty... I had mine replaced and my mileage went from 13-14 to 17-17.5 80%-85% city and the rest highway. I have a light foot as well. The gains include my duals tho

 

Glc---can you advise if RP's gear oil is PAO stock or not?? And why would the Trans temp RISE instead of fall using a synthetic fluid?? I suspect something else is to blame and its just a weird coincidence.

truck guy---yea, I have the Motorcraft fuel filter already bought, but I don't know when the best time to replace it would be. I just filled up with a quality gas and put a bottle of Gumout with Regane in. Should I wait until I fill up AGAIN before I replace the FF, or go ahead and do it now? Or does it even matter?--DirtySCREW

 

I don't think the base stock of a gear lube has as much effect on it as it does with motor oil. With that said, I have no idea what kind of base stock *any* gear lube is. Maybe Labnerd has a better handle on this.

 

You don't have enough posts to send OR recieve PM.

My email is ---

woods_man@hotmail.com

 

OK, I'm not always the best at relaying technical mumbo jumbo, but I'll give it a try...

A synthetic fluid will be more efficient than a conventional fluid, period. But what does the fluid do? Number one, it cools the component. How? Heat transfer...it soaks up and carries heat out of and away from the component you are cooling. Synthetic fluids can and usually do a more efficient job of extracting heat. This efficiency can be seen in the form of higher temps than what you may have been used to seeing with a previous fluid. It's simply doing it's job...better.

The key is to not get caught up on raw numbers just because you immediatley noticed an (slight) increase in temps immediately following a fluid change...especially a change to something as good as the Amsoil ATF. The thing to pay attention to is learning how it operates after that...watch how it may run cooler under stress than before. There's definately not a problem here. Every motor I've ever swithed to Amsoil on after using 'some other' oil, I notied an increase in oil temps under certain conditions, most of the time is was at idle or low rpm driving. Very slight increased mind you, but we're just the type of people who notice things like that. BUT, what I also noticed, is how afterwards, my peak temps under certain conditions were lower and my water temp stayed lower. Even though the oil temp needle indicated higher (sometimes), the overall performance of the motor just felt cooler, if that makes any sense.

 

so if I'm understanding you correctly, you are saying that the synthetic fluid is absorbing MORE heat and that's why IT's temp is a little higher....but it's overall cooling the motor better??? And i know this is not the correct forum...but why NOT RP in my trans???? What makes their product not compatible with my ford transmission. If it meets or exceeds (I'm leaning on the exceeds part) Ford Specs....why wouldn't it work just as good as Amsoil or MC??--DirtySCREW

 

Don't have an answer for ya on the RP, but the Amsoil ATF is a proven product in these trannys. If it says it meets or exceeds (good job, BTW) MERCON or MERCON V (or just what ever your tranny calls for) then I see no reason you wouldn't be safe to try it.

 

Im not trying saying this for the sake of argument but I just wanted to also comment that when I changed my tranny fluid to full Amsoil, the shifts were 1000x smoother and just felt overall like a much better performing transmission from what I had in there before(I changed mine at 89k miles and prior to changing it I really felt as if the tranny was on its way to the dump).

Id fully recommend Amsoil products after first hand experiencing my truck(when I bought it, I really felt as if the truck was abused with no maintenance) improving drastically with the motor oil and ATF.

 

https://www.f150online.com/forums/tr...-good-bad.html

Posts 4 and 5 were made by professional tranny rebuilders.

 

glc---thanks for the link. I'm a shadetree at best. Obviously there are people on this site that can speak more intelligently than I can on several subjects---transmissons being one of them. In my head I still don't understand how RP could mess up a trans IF it meets Fords Spec. BUT with that said I think I will NOT use RP in my trans and go with something the Professional Builders recommend---either MC or Amsoil...and I'll probably go Amsoil if its priced close to RP.
Just curious-----no problems with RP in the Diffs and transfer case are there. I plan on using RP in front & rear diffs, and transfer case, then like I said Amsoil in transmission.

Thanks again for all the replies guys---DirtySCREW

 

Early 2000's Fords did not get as good of gas mileage as the Chevys did. I think the new Ford trucks are finally meeting or beating the similarly equipped Chevs..

 

Why not Amsoil across the board? If you can't find a local dealer, we have at least one dealer that's a member here, your order can be dropshipped from the closest product center.