About to install a fully built 4l80 what are the recommendation for a good quality dex3 fluid.

 

Cat tdto.

 

How thick is that, and how long will the transmission last with that in it.

 

Using something that is full synthetic....your tranny will thank you. It's not unusual to see temps drop 20 degrees going from regular Dexron to a full synthetic oil. Don't get crazy worrying about viscosity, there not much you can do about it like you can with engine oil. Just get a quality full synthetic that meets Dexron spec. Also, put an aux cooler on it.

Here's an interesting chart showing trans life v. temperature.

http://www.tciauto.com/tc/trans-life-expectancy/

 

I've read that in high performance trans a synthetic isn't good to run because it's to slick. And under extreme loads like boost it will burn the clutches quicker.

 

Bullshit

 

I talked to FLT about this... and Dexron III or VI is okay. I decided to run Valvoline VV370 Dexron-VI Full Synthetic in my FLT Level 6...

 

i run Dex6 because i can get it for $3.45 a quart and it's supposed to be good stuff. At that price i'll change it out every summer

 

you realize the best fluid is whatever someone is running, lol
I have used nothing but cheap (nor really) NAPA Dex 3 or whatever they are calling it, it works fine-I have had the pan off several for various reasons, changing things, fluid always looks fine
some diff brands/types may tolerate temps better, but who knows, lol

 

Hey just reporting what I've read on the interweby. I know it depends on what that person is running I just want to know what people are running and how it was holding up I was thinking just part store brand since I'm changing fluid often.

 

That's like saying that a Duntov 30/30 cam is ok. It was fair in its day, unfortunately its day was over 40 years ago, and there are far better choices available today. You made the right choice with Dex 6. Your tranny will run probably 10-20 degrees cooler just because of the synthetic oil. Yes, it makes that much of a difference.

 

I'm not doubting that this is what you've seen. I've seen it too. This is always what people will do when they have no idea what happened to their car. It's always the oil, be it engine, tranny or rear. Or the type of anti freeze, or..... If you put the critical analysis skills of every car forum all together, you'd probably be able to fill a coffee cup.

If you don't want to change fluid often, put synthetic in, and then start using science instead of hearsay. Get it analyzed by a lab. Cost you $20 or so for each sample, and the results are 100% definitive about the condition of your oil. You'll save both time and money.

 

Ok I'll give it a go.

 

I picked up the Valvoline Dex6 for $6 a quart from Amazon.

 

RPM told me to run cheap DEXIII...

 

I would use what your transmission builder recommends/requires (could prevent a warranty or lack of warranty situation).

In our transmissions, we use/recommend Dex-3.

Dex-6 was designed because of the modern applications that partially apply the torque converter clutch during cruising (mostly in the 6Lxx series of transmissions). This is recommended to be turned off for high performance converters, as it can burn up the friction material (that wasn't designed for it). Hence, Dex-6 is generally unnecessary, and just because something is advertised as "backwards compatible" doesn't necessarily mean it is the best for a particular situation.

 

Cheap brand (auto store brand, Wal-Mart, whatever) Dex III is good for most NA street/strip applications.

I would prefer to see more frequent fluid changes than an expensive fluid in a performance transmission.

My thoughts on synthetic fluid is that "generally" they are more resistant to heat. However even regular fluids have more heat capacity than the friction material used in auto transmissions. If you get the pan fluid temp to 300+*, the trans will need a rebuild anyway.

The exception to this is when you are heating the fluid in the converter due to a transbraked application, especially boosted where you may be sitting on the converter for extended time (5-7) seconds.
In the bigger HP applications, this can build a HUGE amount of heat and the fluid needs to be able to handle that as best as possible.
We've seen the John Deere Hygard and equivalents hold up well in these applications as well as some others that beat the fluid up.

One customer is making around 2000 HP in a turbo'd truck and may sit on the transbrake for 6-8 seconds to build boost. It has seen 700-800 degree fluid temps coming out of the converter.

 

What should a built 4L80 with a 3400 stall see for temps in 80-90° outside temps with normal driving around town?

 

It's mostly dependent on how effective the cooler is. 180 would be normal.

 

FLT told me the same thing. Change it every season.
As stated above I would do what the individual builder recommends.
I'm in Florida an mine runs 175-180.