Is there any advantage to using Amsoil heavy duty trans fluid over just regular Mercron III/ Dexron? This would be used in a freshly rebuilt transmission.

 

Amsoil ATF is a fully synthetic base oil with a more robust additive package, and is what I like to call Valvoline MaxLife Multi-Vehicle ATF on steroids. It's more thermally and oxidatively stable than Dex III and can go longer change intervals. If you plan to use a transbrake, where temperatures can climb 50-60*F for every second on you're on the brake, then it would be a worthwhile investment. If you don't plan on racing it, Dex III will be fine.

That said, I'm partial to HPL when it comes to trans fluid. I've beaten the snot out of their trans fluid and can't seem to cook it. Many of the Street Outlaws are using their trans fluid.

 

On paper...yea it is a nicer fluid
in reality...it doesn't really make much of a difference.
After years of different transmissions and different fluids, here's the general takeaway:
type F isn't as good to bushings as other fluids
atf+4 smells like cat **** so I never recommend a customer to use it...because if the trans ever needs a refresh...I don't want the shop to smell like cat ****
dex3 works in prettymuch any application
john deere hygaard is usually cheap and works great...does awesome when on the brake
schaeffers, redline, amsoil, etc etc are VERY overpriced for the benefit you get from them...if you're worried about standing on the brake for long enough to cook one fluid vs the other...the difference is about half a second to 1 second on the brake...in most cases if you're getting burned down, it's going to cook any fluid you have in there...so you might as well use the cheap **** and change it out after it gets cooked.

My vote is legit john deere hygaard low vis (if you can get it for cheap)
otherwise whatever sams club has on sale...usually always dex3 for undr $4 a qt.

 

I agree (with a few exceptions to transfer cases and AWD power take offs requiring specific fluids to work properly).

After building, racing, and rebuilding countless transmissions... I find this to be true.

 

I found that HPL oil.....competitively priced to the other fancy oils

 

I've seen guys spend $25 a qt on full synthetic high performance compressor oil.
It worked fine...but it didn't do anything special that sams club dex 3 couldn't do

 

What applications are we talking about here? A street car, I'll agree there's little to no benefit. A dedicated drag car will absolutely see the benefit, especially if you're a bracket racer and/or use a transbrake. Mike Murillo uses HPL Pro Racing ATF and stood on the transbrake for 9 seconds without it burning down and still ran the number and won the race. The fluid was still in grade and serviceable afterwards per the UOA. There's no chance an off the shelf Dex III could've done that.

That said... does MIke's situation relate to the majority of members on this board? No. Just giving an example of where it does shine. I use a similar fluid in my own car and the trans fluid temps are much more consistent compared to the Dex III I was running before. Shifts are also firmer and converter slips less on the top end as well.

 

I know you're considered the resident expert on anything fluid related on this page...hence your name
I build transbrake transmissions. 80e, 400, 350, glide, etc...and I've had customers stand on the brake for 7+ seconds with hygaard and not have issues.
I would venture that a dex6 fluid (less than $3/qt for full synthetic when I buy it in a barrell) would do the same.

If your converter sees more/less slip on the big end (assuming a non-lockup converter here) then that is almost certainly a factor of temperature and viscosity...not the fluid being higher quality itself.
The same way going from the "standard" hygaard to a "low vis" hygaard will see a stall change on the t brake
or how the switch from mercV to merc LV will see similar change
etc

The additive package and origin of the fluid is not going to make a difference to the fluid coupling properties of the converter as much as the viscosity will.
and yes...many of those guys like mike murillo are in a league far outside the norm compared to almost the entire racing community. But I don't think a single one of them would see a change in performance from switching from whoever their sponsor is (HPL in this case maybe?) to any of their competitors. HPL/Amsoil/redline/schaeffers/lucas/Mag1/etc etc etc etc there are 100 out there and I don't think changing companies would produce any consistently recordable difference in ET/MPH/service life

 

Fluids with a higher pressure-viscosity coefficient provide better coupling as they "thicken up" more under high pressure, giving the effect of a higher viscosity fluid without increasing the kinematic viscosity. I will bow out here though. For the OP's purpose and use, you are right.

 

Right...but most guys in that level of racing are (at least I hope) using a combination of converter dump circuitry, converter pressure regulation circuits, and some even are running converter lockup clutch technology in powerglide and th400 setups.

So...I agree that different fluids can act differently (let's be honest...all of those brands are going to have very minor differences in this regard) BUT...if they're already regulating the converter charge pressure (which really isn't terribly hard to to) then that relationship isn't super critical because they can fine-tune the charge pressure to get the converter to behave as desired.

 

Ding ding ding!

Winnah!

(At least in my experience)

 

This is mainly a bracket racing car. I don't have a trans brake.

 

then run the cheapest **** you can find.
Go to sams club/costco/walmart...buy the cheapest **** they sell...run it