Runaway overheat is triggered by the film strength and additives not being able to prevent metal-to-metal contact. Higher viscosity oils should help with this, I have no idea whether a change from 85 wt to 90wt matters.

 

if it's close to stock (up high) you should be fine.

Got it, good point. in THEORY, a lighter oil that can provide the film strength and additives to ensure contact should be able to protect the trans from overheating more so than a thicker oil though? Though maybe the thicker film from a thicker oil would outweigh that? IDK. probably no difference for me, but interested in trying Motul.

Does Motul MT90 shift smoother than Redline MT85 or MT90?

 

i personally like the 6sp .. bump

 

It's been awhile since I've posted anything on my post I started. I like to thank everyone that loves the 6 speed, and giving advice on what they have done to keep their 6 speed going. I have always used amsoil, but thinking of trying the motul once I get my Evo back up, and going from my build.
MIKE

 

Do not use any 90wt lubricants in your 6 speed. The 6 speeds are designed to work with 75w85 GL-4 lubricant or direct equivalent. The 75w90 stuff is for the 5 speed, and has been known to tear up many 6 speeds that thought they could use the same.

I've always run OEM Diaqueen, or Castrol Syntorq in my 6 speeds. The Syntorq is identical 75w85 GL-4, but it is a full synthetic. It's the OEM fluid for the Neon SRT-4 as well as some other MOPAR vehicles. On my first IX MR I had 360whp, and 182,000 miles on my 6 speed with zero issues. I launched it, autocrossed it, and beat on it. The second owner upped the power to near 500whp and was still on the original stock 6 speed with over 200,000 miles.

I'm currently on my second EVO IX MR with 143,000 miles, but I had the transmission replaced with a TRE 6speed at around 100,000 miles. I have used Syntorq and Daqueen only in this one as well. Zero issues so far.

1st through 3rd gear in the 6 speed are every bit as strong as in the 5 speed. The issue is heat, and 4th gear. There are 6 gears in the same 5 speed housing, so it can't hold as much fluid, and has issues dissipating the heat. This usually happens during road course racing, and 4th is usually the gear to go. If you want to protect your transmission, get a transmission cooler installed. This will allow for more fluid, and more cooling, and should just about fix the reliability issues of the 6 speed. For daily driving, and autocrossing though, you should be fine.

 

I believe that razorlab proved that more than cooling is needed. After he broke his original six speed, he rebuilt it with a transmission cooler and pump, and he still killed it on the track.

 

Besides the OEM and Pennzoil Syncromesh, all I've ever ran was 75w90 stuff. Either Amsoil or Motul. That's good to see other stuff working. But Ill stick with the Motul and see what it can handle

 

You're wasting your time telling people to use OEM trans fluid. Every builder I've emailed recommends OEM yet people insist on using other fluids.
I'm good at 127k miles on nothing but OEM.
I haven't looked into the SRT stuff, though I have heard of it. Probably cheaper too.

 

The SRT fluid is identical, but fully synthetic. The price is close to the same, but it's much much easier to get a hold of because every Dodge dealership keeps the stuff on hand. Chevrolet also has the same fluid sold under a different name. No one ever has Diaqueen on hand, and it's always a pain to order, so I've always just gone with the Mopar fluid.

 

Yup. Castrol Syntorq LT. It's also the OEM Viper fill. It solved my 2nd gear notch/grind when I switched over from the DiaQueen. I'll be putting it in my Shep 6 speed. Shep recommends the RedLine lightweight shockproff, but someone on here said it clogged up his 6 speed and the trans went kaput.

I will say the Castrol/Dodge fluid losses it's "touch" or slickness about twice as fast as recommended refills. So I change out ~7500 miles instead of 15,000 miles.

The SynTorq LT is an interesting fluid. LT stands for low temperature, which is what it's designed to do...keep temps low

 

Very interesting you guys wait that long to change your fluid. The most I've gone is 5-6k miles in Amsoil. So I guess as far as longevity, I don't have much insight for the fluids I use. I like changing mine at 4500-5000 miles. Just piece of mind for me. Plus my Trans is still in one piece, so I guess it's working in my favor

 

Theoretically, if they are okay swapping at 7500k+ then you are okay at 4500. The fluid could only be in better shape.
Worst case scenario, you're wasting money, But really, what is peace of mind worth? Lots of people spend far more money on their cars for "just in case" reasons. I wouldn't worry about excessive fluid swaps.

 

I think the Mitsu OEM recommended interval is 15,000, but I haven't checked in awhile since I do it when I feel a change in how the transmission shifts...usually around 7,500 or so.

 

So I just came across Brad Penn 80w90 GL-4 trans fluid. Has anyone ever looked into it? I Really like Brad Penn oil. I may try this fluid for my next trans fluid change. If you buy it by the case of 12. It's under $10 a quart.

 

I prefer only putting full synthetics in the 6 speed. But be a guinea pig if you choose