Alwyn678

How often does transmission oil need to be changed? Any brand recommended?

garrettb

Most people say you can’t change it enough. I’m not sure what transmission you have, but I use the Pennzoil Dex/Merc stuff because it’s readily available locally.

TimAT

A lot depends on how you drive it. I run my pickup 50k miles. If I was working it hard I'd drop that to 25k. If it was a race application, every couple of weeks. IF it builds heat, the fluid oxidizes-

Use a good quality Dexron- Not sure what the latest revision of that is. Maybe 6 (VI)?

Peterbuilt

The service manual says every 24,000 miles, however, this link (if you scroll way down to the 'Maintenance Schedule) suggests every 30,000 miles.

https://www.corvsport.com/1974-c3-co...nd_Lubrication

drwet

March 2018 Car Craft has an excellent article on ATF. Should still be on the stands. When I was running an automatic I used to use Type F because my transmission shop told me it was better. If you are already running Dexron don't change it to Type F. I don't think they are compatible. On my daily drivers I change it at about 60K miles.

Big2Bird

REELAV8R

Dex/merc Valvoline Max life full synthetic for my TH350.

It's full synthetic and it relatively cheap in a 4 quart jug at walmart.

jb78L-82

When I had a turbo 350, as someone already mentioned Ford type f is the best. Sold the Nova SS with 170,000 miles on the tranny and the turbo 350 was still going after beating it to death for years.

Honestly, do NOT follow the manual on any car about tranny fluid intervals...at best take what they say and half the miles. I would NOT go more than 25-30,000 miles for Max tranny longevity and always with a filter change. I change my dd's at 20,000 mile intervals.

Always running an external additional trans cooler and changing the fluid often with a new filter are much more important than fluid brand. I currently have an 01 grand prize with 210,000 miles on the fwd 4T65E and Chrysler 300 at 160,000 miles... Walmart brand super tech tranny fluid....

gkull

Type F has more friction additives than dextron. So your clutches... grab better instead of warring out.

If anybody beat on a th350 for 170,000 miles they just didn't have enough power Mine never lasted even after being built up to take on big power

jb78L-82

Gkull,

That is funny..I was in High School and through college with a stock 73 Nova SS with LTH's.....not real power by any means but I used to do burnouts all the time...

TimAT

Type F fluid in a TH350 or 400, will work pretty well. Using it in a TH700-R4 or 200-4R, the trans will be unhappy. The bearings and planetary gears have tighter tolerances and the Type F won't lube them as well. At least that what the Transmission instructor guy at GM Training told us when we did the early 700-R4 class.

Big2Bird

And you think they would have said Ford at GM training class?(JKTim)

7T1vette

Any good quality full-synthetic trans oil would be better for the transmission....IF the clutches are compatible with that oil. Full synthetic oil is much more heat tolerant, so it won't be damaged by some extra heat when being worked hard.

Your GM instructor didn't understand the benefits of full synthetic oil for long-life of 'working' parts.

jb78L-82

Here is the thing about automatics..they do NOT like high temps and I don't mean really high temps where a synthetic would have better resistance to breaking down. Generally, "normal" temps that a tranny fluid runs is too high for max transmission longevity, regardless of the fluid type, semi synthetic or full synthetic. Running an external trans cooler is vital to max transmission life as well as changing the trans pan filter often....the filters in most transmissions are not extremely effective over a long period of time since they are too small, thus you need to change the filter much more often than 50-100,000 miles which is the typical manufacturer recommendation. Heat and dirt kill transmissions....

Since I change the fluid and filters on my 2 DD's automatics every 20K and both have 36,000 GVW and 28,000 GVW coolers outside of the radiator cooling, there is really no need to use a full synthetic. I use Walmart super tech in both since you need to drop the pan to get to the filter and I would rather use fresh fluid, then risk a longer mileage interval (and a dirtier filter) using a full synthetic. The 01 Grand Prix currently has 210,000 miles on it and going strong and the 08 Chrysler 300 has 150,000 miles on its transmission, both showing zero signs of any issues....BTW..neither of these transmissions are known to be super tough...that is being extremely kind.....

On the other hand, in my 1994 Mustng GT 5.0 with the AODE (transgo shift kit as well) with 42,000 GVW coolers outside of the radiator cooling only, I do use Mobil 1 synthetic (12 Qts) but I only change this fluid every 7-8 years since the car is driven less than 1,500 miles per year....

I have been doing the transmission maintenance now on many cars for many years and have NEVER had a tranny failure..ever:

Use a decent trans fluid
Changes the fluid often
Change the filter often
Always run at least an external cooler in conjunction with the radiator cooling or BETTER an external cooler that does all of the trans fluid cooling which is what all my cars are setup to do for the last 30 years and counting...

Big2Bird

I'm quite sure when Tim took the class in the 80's, there was no synthetic.

jb78L-82

This comment is 100% spot on....

7T1vette

The only items in an auto trans that really care about heat are the seals, clutch plates and THE OIL. The seals and clutch plates are good for well over 300*F; the oil is not.

Either cool the oil down with an external oil cooler ADDED into the system or install synthetic oil in your trans.

jb78L-82

Sorry..do not agree...synthetic oil is NOT a replacement for an external trans cooler....For maximum trans longevity you must have an external trans cooler...adding synthetic is additional insurance..not a replacement.
All severe duty and racing applications today even on modern cars ALL have external coolers, regardless of the transmission fluid type...

BTW-If your fluid temp spends any time over 240-250+ degrees, you can kiss the tranny goodbye.........Synthetic fluid will run about 10-20 degrees cooler than semi synthetic and will last longer BUT high trans fluid will kill the seals..they are not immune to high temps as stated earlier..not true!

Not sure where you are getting these figures and comments...??????

The ideal trans fluid temp for maximum tranny longevity is 140 degrees....OR LESS but very difficult to achieve even with BIG double stack coolers as stand alones and impossible if you run coolers in conjunction with the stock OEM radiator cooling....all year round cooling-summer and winter (obviously easier in frigid temps).

Big2Bird

Interesting point.
My 2017 Silverado with 6 speed auto has a thermostat in the tranny cooler set at 190*. I "assume" it's a millage deal, although I would think if it was a warranty issue they would adjust it lower.
The cluster does have a factory tranny temp display.

jb78L-82

Actually it is a mileage per gallon issue and drive ability challenge since very cold temps can effect a trans ability to shift correctly if the fluid is too cool. My 01 Grand Prix with 210,000 miles on it will not shift into OD until the trans fluid get over 88 degrees...it can be delayed for a few miles in artic temps like we are experiencing now. Most tranny's today will easily go 100,000 miles which easily exceeds the mileage warranty. Case in point is the foreign makes like BMW, Mercedes, Lexus/Toyota etc that use a "sealed for Life" synthetic fluid...THERE IS NO SUCH THING!

I know personally 2 folks who did not change their tranny fluid ever and one at 110,000 miles and the other at 125,000---trannys were toast. Lexus does not even cool their fluid with in radiator cooling system.Theey use a VERY small heat exchanger with coolant to "heat" the fluid faster for better mileage.......