In a previous post, I mentioned that my transmission "burped" after towing in high temperatures and up a steep hill. I bought the larger Dorman 6.0 cooler that I'll be installing soon. I was going to switch to full synthetic fluid, but after reading a lot of transmission threads, I'm starting to doubt that it's really necessary. So, that leads me to two questions (hopefully Mark K. will chime in here). Is the full synthetic worth the extra cost or will taking it to the dealer and having them flush the system work just as well with the new, larger cooler? The second question involves the filter. If I do decide to go full synthetic, is it necessary to drop the pan and change the filter? The truck has 65,000 miles on it and I don't know when or if it was changed in the past.

 

I believe the only real advantage to synthetic is it has a higher thermal degradation point than conventional. I beat mine hard and it gets warm often, so I went synthetic. I bought it in batches as part houses had sales on it to keep the cost down. Granted I had to buy enough to fill a dry converter as well. Anything below 220* for TFT is fine and dandy, don't exceed it for very long if you do creep above (20-30 minutes).

Wouldn't hurt to change the filter for peace of mind, keep in mind the pan gasket is reusable and most aftermarket ones suck at sealing properly.

While you're at it, why not add in an external spin-off ATF filter? Easier to maintain and you'll never really have to worry about the in-pan filter again.

I'll tag Mark and see if he has stuff to add... @Mark Kovalsky

 

Full synthetic has better thermal resistance, i.e., it won't degrade at high temps as easily as conventional. But conventional fluid is good for over 250°F, so how hot are you planning to get it?

The only time you need to change the filter is when rebuilding the transmission. Anything short of that, including changing to synthetic, does not require a filter change.

 

I just did mine last night with Mobil 1. It shifts a lot smoother. If you do it yourself make sure you have the right size hose hooked to the rear cooling line. Mine was little big and clamping it was tough and had some leaking and made a mess. I figured with as much as it would have cost to have it done at a shop with conventional fluid, I decided that I could do it for about the same cost using synthetic

 

how much is the dorman cooler supposed to help temp wise over the stock 6.0l transmission cooler? I go over a couple passes often and hit 210-220 and it would be nice to be able to drop it and increase the lifespan of the transmission.

 

Well Dorman is off-brand stock replacement parts, so I'd imagine it's about the same effectiveness...

I have been running a Hayden Class A motor home trans cooler from O'Reilly's in the Chevelle as well as my X with good success. The car has a 3000 stall so it makes a LOT of heat driving around town. The X got it when my in radiator cooler line sheared the fitting and I needed an alternative. Running the Hayden in line with the crap stock 7-row has been good, averaged 160-175° on the stock transmission. With my built trans I'm seeing 170-180°, creeps to 200° when I flog the absolute hell out of it (full throttle sprints over 110mph, etc). Built trans averages about 5-10° warmer than stock, which I was expecting since the tolerances were closed up a bit and extra frictions and steels added.

Having said all that, I have a big 6.0 cooler that's going in soon as I have time and replacing both the current coolers.

 

Exactly zero. It was not designed as an improved cooler, it is a direct replacement for the 6.0L cooler.

Your temperatures are in the normal range. Lowering them won't help the lifespan of the transmission.

 

Are there any real advantages to doing it yourself, vice taking it somewhere that uses a machine to do the job? I mean other than the satisfaction of the DIY experience and the cost? I don't currently have anything that will hold 5 gallons of fluid, so I'd have to purchase a bucket/container and then I'd have to dispose of the old fluid. I do a lot of work on my cars myself, but I'm wondering if this isn't something that would be easier to have someone else do. Unfortunately, I don't have anyone around here that does transmission flushes with Mobil 1, which I'd prefer. My choices are Valvoline Maxlife, Castrol Transmax Synthetic or taking it to the dealer for Motorcraft.

 

There are three advantages to doing it yourself in my eyes.
1. The satisfaction of doing it yourself.
2. Less cost.
3. You can use whatever fluid you want, not what the shop uses.

Many places will take used oil. Walmart does, Auto Zone, etc.

 

4. You know it actually had a full flush vs just a pan drop and refill.

 

Are you guys flushing your transmission or just draining and refilling them?

 

I flush mine. That changes about 95% of the fluid, which is a lot more than you can do any other way except taking the trans out and tearing it down.

 

I've been convinced to do it myself. It really doesn't look that hard and I can always use a spare bucket, especially one marked in quarts and gallons.

I've been doing some reading here and on other forums and there seems to be a lot of people who really like the Valvoline Maxlife Dex/Merc Full Synthetic and are running it in their 4R100. Their product sheet lists it as being suitable for use in Mercon applications and I can get 5 gallons of it at WallyWorld for around $90. The best price I've found for Mobil 1 is around $9 a quart which would double the cost. So, I think I'll give the Maxlife a shot. Thanks for all of the input.

 

I'm hoping that within the next couple of days the rest of what I need to install the 6.0 trans cooler will be here. I'm thinking that the best sequence would be to install the new cooler and run the Ex for a while to make sure the cooler gets filled with fluid and it gets rid of any trapped air in the system, then do the flush?

 

Hey Mark,

How necessary is it to flush the transmission after a rebuild? I just bought $250 worth of Royal Purple ATF and don't want to waste that if I need to flush the transmission after a couple thousand of miles.