Discussion Forum - Northstar Chevelle Club

Bowtieman427 · Active Member

What ATF do you run ?

Chris R · 2K+ Club

Dexron III.

Lost in the 60s · President

Not sure that a trans/hydraulic oil would be good for an automatic only. That oil is specifically formulated to run the hydraulics too and may be too heavy for a car trans. Looks to be REALLY expensive also...

Since heat is what kills an automatic, the BEST protection for a high performance auto trans is to get the oil out of the radiator and thru a large, external, cooler mounted in a high air flow area. The small coolers in the radiators are insufficient to cool the fluid and the oil won't ever get any cooler than the coolant temp, which runs very high itself.

67ss · 1K+ Club

I have heard of people running hy gaurd in race cars only that are just run on the track. But I don't think that would be good for a car driven on the street. As Mitch said a good tranny cooler and synthetic fluid would probably be the best bet.

SShink · 3K+ Club

Lost in the 60s wrote:

Since heat is what kills an automatic, the BEST protection for a high performance auto trans is to get the oil out of the radiator and thru a large, external, cooler mounted in a high air flow area. The small coolers in the radiators are insufficient to cool the fluid and the oil won't ever get any cooler than the coolant temp, which runs very high itself.

Just saying what John at Master Trans told me when I asked these questions for a 'mild' street car:

-No external trans cooler required with a 3 or 4 core radiator, it's enough cooling through the rad

-Use Dexron III fluid for the GM trans, it's fine to run on the street

That's about it, so that's what I'm going with. If I have heat related problems, he'll be the one fixing them...

Bungy L-76 · Active Member

Dextron III for autos and Redline MT-90 for manuals. I always run a trans temp guage and an aftermarket cooler on autos. Definetly run an additional cooler (besides radiator) if you have a high stall converter. My 2 cents.

Tony Hoffer · Moderator

Mobil One synthetic ATF..

John D · 2K+ Club

About trans cooling:

Can't remember where I read it, but it makes a TON of sense...(summary)

- We know that hyd/trans fluid will break down at temps exceeding 250+ degrees...
- We also know that transmissions don't like to work properly, or things break when "stuff" isn't warmed up...

Properties of heat transfer 101.
When you're grinding/heating/welding/whatever on something, and you're done with what you're doing to it... what do you do?

1) dunk it or wipe it with a water/wet towel
2) let it sit and air-cool

Be honest... you dunk/wipe it. Why? Because it cools down FASTER!
Water is a much better conductor of heat than air.

Same thing with transmission fluid.
Running the trans cooler lines into the radiator cooler achieves 2 things:
1 - will bring cold fluid up to operational temp faster
2 - will bring hot fluid down to into acceptable ranges

Most reputable trans builders will recommend running the cooler lines into the radiator cooler 1st, then to an auxiliary cooler, then back to the pan. Why?
- The 1st "fluid to fluid" step will either rapidly transfer the fluid temps up or down into the optimum range.
- The aux cooler will further stabilize/lower the fluid temp, and then when this fluid is mixed back into the pan fluid, it will then lower the sump (freshly worked) fluids temp.
- This process as a "system" will lower the workload of both the radiator cooler and the aux cooler and produce a more stable fluid temperature.

(Most of the newer cars even have a temp sensor on the trans cooler lines. The CPU won't allow OD or convertor lockup to happen unless the fluid temp is in the operable range.)

Our cars are usually used in a manner exceeding the design parameters of the original (fluid to fluid) cooling provisions - hence the need for an auxiliary "fluid to air" cooler (read that heavy-duty or RV).

I'll tend to go with the engineers on this one...

seagrams72 · Active Member

Type F, it is bascially the same thing as B&M trick shift or whatever their aftermarket fluid is.

Pushrod · Active Member

I had a 200-4r "extreme duty" trans built by Bowtie Overdrives they have done extensive research on trans oil and their position is....Dexron III, buy it on sale at napa or where ever. when you change oil in the engine pull the trans pan, whatever drains, refill with that amount after 3 or 4 oil changes change filter in trans, cheap and easy. Trans fluid temp, if cooled properly, assuming trans is set up properly should never get hot enough for for any length of time to damage anything.

Clutch · Member

Tony Hoffer wrote:

Mobil One synthetic ATF..

I'm a big beliver in synthetic for trannys that get street miles with big converters.

4-door Chevelle · Super Poster

What John D says is what I do. I added the external cooler when I put the higher stall convertor in, it was strongly suggest by Midwest Convertor who built it for me. I also added a temp gauge and monitor it in the line prior to entering the radiator. I will hit 230 occasionally when pulling away from the light ... pullng the pop-up camper of course but it colls down good once we are up to speed.