How hot should the tranny get?

[justbinfishin]

I have an m50d-r1 tranny, and lost a bunch of fluid, started making noise the other day (A concern voiced in my previous thread from this morning). No noise since I topped it off. I topped it off every 50 miles till I made it to a friend's shop, and I noticed that the fluid was about 150 degrees. Not too hot to stand, but not comfortable. I've never touched the transmission before it cooled down for a fluid change, so I'm wondering if this is normal? When I get the new engine in I"m gonna put 300 miles on it with the trailer before I decide to continue up the ALCAN. I wonder if running it in 5th with a 900lb trailer and 400 in the bed is what made the fluid boil off in the first place.

 

[adsm08]

A higher gear should have little effect on trans temp. The trans does get pretty hot, but I don't know that there is a particular spec for trans temp. I know mine got pretty hot when I was still running with my floor open around the shifter. I could burn myself on the top of it.

5th gear is still excessive for that kind of load. I wouldn't go above 4th.

 

[shane96ranger]

I topped it off every 50 miles till I made it to a friend's shop.....

is what made the fluid boil off in the first place.

At your friend's shop, what did you do to fix it? By the second statement, are you under the assumption the fluid "evaporated" because it boiled? It's more likely you've got the 3 plugs cracked/missing up on the shifter housing. That's where damn near every M5OD loses it's fluid. Also, I don't think 150 degrees is abnormal. What motor and gears do you have?

The three plugs are the three black (albeit very dirty) circles under the shifter.

 

[justbinfishin]

I am aware of the plug issue, I checked and they'd already been pulled and RTV'd. I've always wondered though, since the tranny can still vent through the shifter, wouldn't the fluid boil off slowly regardless of whether you seal the plugs? I'm almost certain it's the rear output seal, I dropped the tranny/tcase and gonna split them tonight to validate that. It only lost fluid when I was pulling long hills, so I'm almost certain that's what's up. I should also have mentioned that the fluid was changed/topped off 1100 miles ago when I started my trip, so it lost a quart in that distance, which seems too rapid for the fluid to boil off unless the tranny was way overheated. I'll update when I know if the rear what's leaking.

 

[justbinfishin]

I know mine got pretty hot when I was still running with my floor open around the shifter. I could burn myself on the top of it.

5th gear is still excessive for that kind of load. I wouldn't go above 4th.

It pulled fine, but it was unnecessary strain I agree, so I'll stick with 4th, and also I pulled the cupholder so I can feel the top of the tranny, and I'm not even close to being able to burn myself on it at its hottest so I'm hopeful as to my tranny having life!

 

[mk42gunner]

The bad part about losing fluid when pulling up long hills is that the oil slinger, (which lubes the small set of needle bearings between the input shaft and the mainshaft) is fed by oil splash from the front of the gearcase. Low oil level, front of truck up, less oil going to the slinger = bad news for bearings.

2X4 or 4X4?

I would put a new output shaft seal in it and fill the transmission; then raise the front of the truck for a while to see where, or if, it is still leaking.

I don't know what temp a manual tranny typically runs at, the only time I ever felt one was when I was trying to diagnose a problem; but I don't think 150 degrees is out of line. I do sincerely doubt that ATF boils at 150 degrees though, oil in a deep fryer doesn't really start moving until about twice that temperture.

Can you tell where the fluid is leaking from? A quart in 1100 miles seems like it should be fairly obvious; but maybe not if there is no dirt to collect the oil.

Robert

 

[justbinfishin]

So I am at a loss about this one. Dropped the tranny, no leakage out of the plugs (didn't expect that, someone RTV'd them already), nothing out of the rear or front seals, and nothing out of the shifter. Had a tranny professional look at it (he's rebuild dozens of the M50D-R1's) and in his words "there is nothing wrong with this transmission, the bearings are tight and the gears look good. Also, where the heck did it lose fluid from?" Perhaps I filled it too fast when I chaged the fluid pre-trip, and it splashed back from a gear or something and I thought it was full? At any rate, I'm gonna forge ahead day after tomorrow (got the new engine in, gonna test run it tomorrow for 200mi). I am stumped by this one.

 

[AllanD]

150degrees F is on the low side of normal. for a Mazda transmission.

wanna really see one get hot? try a long steep uphill climb at 55-60mph in 3rd gear towing a 4000# trailer (or a minivan on a tow dolly).

Generally speaking the transmission will run coolest in 4th gear.

While everything inside the trans is spinning the gears are not involved (even slightly) in power transmission... because in 4th the trans is in "direct drive", the input shaft is quite simply locked to the output gear.

So even saying "4th gear" is a misnomer.
Yep, one I often indulge in myself, but I actually understand the irony.

AD

 

[doorgunner]

I would think that the manual trans is going to stay near the same temp. as the engine because of heat transfer...except in heavy towing conditions

my A/T ran at 190-210*F until I put a oil cooler on it....now it runs at 150*F

fabbing a air scoop to direct air onto the 5-speed couldn't hurt....

and yes......150*F feels HOT........180*F will make you yank your hand off the case real fast!

 

[AllanD]

I actually took the time when mine was last apart to drill and tap a 1/8"NPT hole in mine for a 150C VDO oil temp sensor, I've never seen it get past 110C, but even that makes you want to move your Right foot away from the tranny tunnel.

The other thing other than thermal conduction is the fact that the
Catalytic converter is right alongside the trans, and a dirty grey
trans absorbs heat from the Cat.


On a long uphill climb while towing that cat is sometimes literally glowing
from the heat

That is why I took the time to acid etch my transmission case, use Zinc chromate
primer, then paint it a bright metallic silver to reflect away as much heat as possible.

I was planning on making a sheet metal heat shield, out of polished stainless steel of course,
but I just haven't gotten to it yet.

I also have a bare case on my workbench and I'm trying to figuire out how to do two things...
One use a small pump to take oil from the trans, pump it through a heat exchanger, then a
replaceable filter, and then return the oil to the critical parts of the trans via squirt jets to
deliver that clean cool oil to the most critical parts of the trans

 

[mk42gunner]

...I also have a bare case on my workbench and I'm trying to figuire out how to do two things...
One use a small pump to take oil from the trans, pump it through a heat exchanger, then a
replaceable filter, and then return the oil to the critical parts of the trans via squirt jets to
deliver that clean cool oil to the most critical parts of the trans

AllanD,

Please correct me if I'm wrong, it has been a few years since I had an M5OD apart.

What about replacing the sheetmetal trough that feeds the oil slinger with a tube from the pump, and removing the delicate oil slinger completely? This would hopefully feed a decent supply of oil to the needle bearings between the input and output shafts. That bearing has my vote as the most critical one in the transmission.

I know from painful experience that if you crack one of the oil slingers when putting the transmission together, that you will get 453.7 miles on an 88 F150 before the input and output shafts weld themselves together. Makes it very hard (impossible) to get apart afterwards too.

Robert

 

[AllanD]

AllanD,

Please correct me if I'm wrong, it has been a few years since I had an M5OD apart.

What about replacing the sheetmetal trough that feeds the oil slinger with a tube from the pump, and removing the delicate oil slinger completely? This would hopefully feed a decent supply of oil to the needle bearings between the input and output shafts. That bearing has my vote as the most critical one in the transmission.

I know from painful experience that if you crack one of the oil slingers when putting the transmission together, that you will get 453.7 miles on an 88 F150 before the input and output shafts weld themselves together. Makes it very hard (impossible) to get apart afterwards too.

Robert

That little "slinger" is actually a pump designed to draw oil
from the front retainer and drive it through the pocket bearing.

That little slinger is necissary, because otherwise oil would need to flow
against centrifugal force to get into the pocket bearing.

Depending on something unlikely for survival is engineering suicide,
so ford used that little plastic turbine, I used to try real hard to get them
off intact and if there was the least doubt to break it in half and drop it in
the trash before using a new one.

That little plastic slinger is argueably the most important part of the transmissions
lubrication system

I could do what you suggest but in the front even a low pressure
pump is likely to overpower the input shaft seal, I'm not wild about the idea of not
only blowing my oil supply out of the trans but blowing it all over the clutch disc.
the next issue is should the pump stop working, for whatever reason,
the life of the transmission would be short afterwards.... IF you completely defeat
the "splash oil" flow path.

at the back of the trans the little spouted cup that feeds oil
into the tailshaft for the 5th and Rev "float" bearings also
needs clean oil but that is easier to route an oil feed line to

What I'd think about using is a low pressure rotary vane pump,
like a Holley Fuel pump. the real point is tapping oil out, filtering it,
cooling and putting it where it needs to go. the rest of the transmission
can take care of itself.

So I have no intention of blocking off the splash oil,
just supplementing it

 

[PlumCrazy]

Have you considered using an oil pump from a BW RBV tcase?

-PlumCrazy

 

[PlumCrazy]

Nevermind, those pumps require machining a hole through the shaft. I could see that being a week point.lol

-PlumCrazy