Redline MTL vs. MT-90

[AUSMHLY]

I've read about some of us using Redline instead of straight weight 30 non detergent oil in our transmission. I'll assume most of the transmissions have the overdrive.

My question: which Redline is the favorite here?
MTL or MT-90?



This is from Redlines website:

Synthetic Manual Transmission Lubricants

Red Line Oil's MTL and MT-90 are designed to provide excellent protection and improved shiftability for manual transmissions and transaxles, having cured the problem of hard shifting in thousands of transmissions with shifting troubles. How? They have the appropriate coefficient of friction for most manual transmission synchronizers (many gear oils, engine oils, and ATFs are too slippery for proper synchro engagement). And, the wide viscosity of MTL and MT-90 allow proper shifting over the entire temperature range which the transmission will experience. The synthetic base oils used have a very high viscosity index which provides relatively constant viscosity as temperature changes. MTL is a low 70W at very low temperatures and a high 80W, nearly an 85W, at elevated temperatures, providing adequate viscosity to prevent wear and deaden gear noise. MT-90 is a thicker 75W90 version of MTL. The shear stability and oxidation stability of these products are excellent, thus the physical characteristics of Red Line MTL and MT-90 will change little with use.

MTL
This 70W80 GL-4 Gear Oil (SAE 5W30/10W30 engine oil viscosity) is designed for use in manual transmissions and transaxles. Provides excellent protection of gears and synchronizers and its balanced slipperiness provides a perfect coefficient of friction, allowing easier shifting. Popular in many BMW transmissions and in most Honda and Acura transaxle applications.

MT-90
Popular in Nissan, Toyota and Mazda manual transmissions and transaxles as well as other selected applications, this is a 75W90 GL-4 Gear Oil that’s slightly heavier than MTL. Provides excellent protection of gears and synchronizers and its balanced slipperiness provides a perfect coefficient of friction, allowing easier shifting.

 

[Ed_K]

Hi Roger,

I tried MT90 for a while. It seemed to find it's way out of the seams of the transmission a lot easier than regular motor oil. It is highly recommended by Dave R. My transmission shifted smoothly with MT90.
Because of marginal operation of my over drive ,( nothing to do with MT90), I switched over to 60w Valvoline VR1. My over drive works perfectly now. I think the 60W VR1 is making up for a worn seal in my o/drive accumulator. If you read old posts by Keoke, you will see that he has run 60w VR1 in the summer and 50W VR1 in the winter time for the last 20 years with no transmission or o/drive problems.
Unless you are having some problems with your transmission or o/drive, I would stay with a regular motor oil. Others opinions will vary.

Ed

 

[tahoe healey]

I use MT-90 and like it. But it does leak a lot. A pain with having to remove the radio to check the level. Ed, do you find substantial improvement in the leaking?
Roger, what are you running with now? Are you having problems that make you want to change?

 

[healeynut]

Weird - I have MT90 in my BJ8 and I get less leakage with that than I did with Non Detergent 30 wt. I haven't had to add any in like about 6 years.

MT 90 is the way to go.

 

[RobertM]

The main difference between the two is the MT 90 is recommended in hotter climates. I us the MT 90 here in Atlanta and have had no problems. Bob

 

[AUSMHLY]

Hi guys,
I finally got my transmission repaired. (My mechanic and I took it out 5 times untill we found the right commbination of gears that worked with each other. Another story for another time).

I run 20-50 Castrol now. As per my mechanic. I've read some good things about Redline here. Do I leak, of course. A lot? Don't think so.

When cold, a little effort is needed to get into second gear. Once warmed up, goes into second a lot easyer. Is this how BJ8's normaly are?

Wondering if Redline would help with second gear. Or if the improvement overall with all gears is worth the bigger drip spot(s).

So, if switching to Redline, the question then would be, MTL or MT-90.

Looking forward to your replies.
Cheers, Roger

 

[Randy Harris]

Roger,
I switched to MT-90 in both cars a few months ago from (I think) Castrol 20/50. I've noticed significantly larger drips on the floor since the switchover. Haven't noticed any appreciable difference in shifting or tranny noise. Given the added cost of MT-90 I don't think I would do it again.
Randy

 

[tahoe healey]

But from where is the drip comming from? Can it be stopped with better sealants?
Roger, why did you have to change gears around? The BJ8 has a great system for the period. I had mine gone over by the best, Bill Boulton, and it is sweet and all original. The PO had left out the detent balls and springs which made the shifting sloppy and noisy as the main shaft slowly disintagrated. You should not have to mess with the gears and I hope you saved the originals cause they can be expensive to replace.(or sell them on Ebay)

 

[Michael Oritt]

I use MTL in the Toyota transmissions in both Healeys. No problems and no dripping. I change tranny oil annually on the Healeys regardless of mileage, probably just as an exercise.

I use MT-90 in the MGA close-ratio (synchro) box in the Elva race car. I have not had this transmission apart but it has some "issues": I can beat the synchros on fast upshifts though it just a slight crunch; the lever occasionally pops out of third on downshifts, the box leaks alot, etc. etc. But it definitely performs MUCH better on Redline than on Castrol and slightly better on MT-90 than MTL, I can only guess because of the higher viscosity. I change tranny oil on the Elva about every third race weekend.

 

[AUSMHLY]

Roger, why did you have to change gears around? The BJ8 has a great system for the period. You should not have to mess with the gears and I hope you saved the originals cause they can be expensive to replace.(or sell them on Ebay)

TH, I didn't change the Healey gear system, what I meant was nos gears are hard to find. The replacement gears/parts available from the usual suspects are not as good. The replacement ones look good to the eye, but tolerances are off. You find this out once installed in the transmission, under running load. So you re-open the tyranny, take that part out, send it back and try another source, till you find gears that work with each other. Hence the 5 times we R&R'd the tyranny. I did find a nos 1st gear assembly on Ebay. How lucky was I. If we could replace worn out parts with nos, fixes would be simple and done right the first time. Trying to find the parts, along with acceptable tolerances is part of the battle.

Now that I have a working rebuilt transmission, I'm just trying to get that last bit of improved performance out of it. Hence the question if Redline provides that. And if so, would it be MTL or MT-90.

Cheers, Roger

 

[healeynut]

Roger -

You are in San Leandro. I am originally from the Bay Area. It is a relatively warm climate, esp. if you go anywhere outside the bay area on a drive. Use MT-90. It is the way to go.

20W-50 is not the right stuff - the friction inhibitors in multiweights make the shifting more difficult.

 

[AUSMHLY]

I found this artical, titled, Oils aint Oils...

https://www.myaustinhealey.com/austin_healey_technical_articles.html

His advise, Redline MT-90.
Interesting read.

 

[Bob_Spidell]

I put MT-90 in my BJ8's gearbox hoping for a little quicker o/d action when hot. I wasn't expecting smoother shifting, but to my surprise it seemed to shift smoother (and the o/d did engage a little quicker when hot).

The MT-90 didn't leak any worse than 20W-50 at first, but I've since had some trouble getting the big brass cap on the o/d to seal.

 

[Bob_Spidell]

Oh, FWIW there seems to be less brass "shake" in the oil at change time than with mineral oil; either there's less wear or the larger particles are settling out.

 

[tahoe healey]

So, is there something we can do th prevent the leaking with sealing the big brass drain? I like the stuff but not on the floor.

 

[AUSMHLY]

TH,

My mechanic uses Teflon (plumbers tape) around both the small drain plug and the large brass overdrive cap. No leaks there! Now if I could just stop the leaks from the other areas.

A couple car show ago, the guy at the entrance said to me...An Austin Healey. That's gonna leave a spot. I replied, if it doesn't leave a spot, then I'll have concern.

Cheers, Roger

 

[healeynut]

Teflon tape will take care of this.

 

[Bob_Spidell]

I've never thought the hard fiber gaskets used on the brass cap were ideal. I've done two things (not at the same time):

1) teflon thread sealant on the cap's threads, and
2) Permatex aviation form-a-gasket on both sides of the hard fiber gasket

I'm currently using the latter and, I just checked, have no puddle on the floor. I've also thought of soaking the gaskets in oil to soften them up, but haven't tried it (might be recommended, but I've never heard so).

I like to put a thin coat of the form-a-gasket on on any fiber or paper gaskets(except on fuel system components). On the fiber gasket under the brass cap, the form-a-gasket will make it hard to remove; I use a propane torch to warm the brass and aluminum around the gasket (not so hot as to melt metal, obviously).

On another note, I've always wondered why they went from the brass cap with a six-sided nut--suitable for use with a wrench--to the one with the notches around the periphery that require a special too. Anybody know?

 

[Ed_K]

Bob... That problem that you describe, " when hot, o/drive doesn't engage " is exactly what I had experienced with regular 30w motor oil.
I switched to redline MT90. That didn't cure the o/drive problem but the transmission seemed to shift a little smoother...
But transmission shifting was NOT a problem with regular 30w and not the reason I tried MT90.
An old post by Keoke on this forum recommended Valvoline VR1 60W in the summer and 50w in the winter. I put in 60w and that fixed the o/drive problem that you described on my car. If MT90 fixed it on yours then your accumulator seals are not quite as worn as mine apparently are.
I think that Dave said MT90 is somewhat equivalent in viscosity to 40w motor oil. If your o/drive starts acting up again when it gets real hot, try switching to 60w valvoline VR1.

Tahoe... The transmission and o/d case were coated with a film of MT90 after only a few thousand miles. The level was not down by a significant amount. In retrospect, I think the film of MT90 was due to the fact that MT90 sticks on the metal longer than regular motor oil and was more noticeable. The regular motor oil also leaked out but was not as noticeable as the MT90. Sticking to metal is a good thing when it sticks to the gears in the transmission. The transmission shifts very well with the 60w and the o/drive has worked flawlessly ever since I put it in the transmission.

Roger... If you are going to use one of the redline oils, use the MT90 which is slightly thicker than the MTL and better for hotter climates.

 

[AUSMHLY]

Nice reply Ed. You touched on everyone's concerns. Right on! This is why I dig this forum. Not only do we get our questions answered, we get them the same day, or the next and with wonderful explanations why it is so.

Ed, I just notice you have inched me out by posting 2 more times than I. As my friends tell me....you have too much time on your hands. lol! My hats off to you.

Speaking of Keoke, I miss his presents here.
Cheers, Roger