legacycentral bbs

Scott brought up an interesting though a while back. Externally cooling the manual transmission fluid. I think it's a great idea. There's nothing that cools the manual tranny fluid except the case being exposed to the outside air. I don't see this as being too efficient. His idea was to have a fitting on the drain plug that goes to the cooler, then have it return to the dipstick. I think there was a pump in there somewhere. That sounds like an easy enough idea, but to me sounds kinda messy, and you'd need a fairly strong pump to do that. I was thinking more along the lines of opening two of the plugs/bolts/whatever on the side of the case, and using those. Does anyone think this is a do-able thing? What kind of pump would be recommended for GL5? I'd assume if ou could find an external engine oil pump it should suffice right? Any thoughts?

sounds like a good idea to me. but then again i dont know the specifics of any of that. heheh

Personally, I don't think it's necessary. diff fluid is a completly different animal then ATF fluid, and is used in different manners.

In MT's, the fluid is used as lubrication, it's not the "working" fluid to transfer the engine's power like in AT's.

Yeah... before you go to the trouble, first measure your gear oil temperatures and see whether there's any need. I suspect you may find there isn't.

Whatever pump you use, make really sure you don't end up frothing the oil up or anything. That'd suck.

Yeah, it's totally different from ATF. It's used for cooling and lubricating though just like engine oil right? I know the GL5 doesn't get as heated as engine oil since it's not right by huge explosions . Wouldn't a cooler fluid help no matter what? I mean not like 50 degrees cool. 6mt's have an external cooler though right? Supposedly some markets with the 5mt get a cooler aswell, but no confirmation on that yet. I suppose it would be best to find out the temp first though.

Well, the fluid has an optimum operating temperature. Having it too cold could accelerate wear and affect shifting smoothness and stuff.

I wouldn't really say gear oil is used for cooling... I mean, it's true that without the oil the friction would cause excessive heat in the gears, but it's not like the oil is really being used to carry away heat that's being generated in the transmission.

Maybe the 6MT uses the fluid for some hydraulic stuff with the DCCD?

It would be easy enough to drill an 11/32" hole in the drain plug and tap it to 1/8" NPT and thread in the probe for a $10 oil temperature gauge.

Hmm, I dunno, if the 6mt used the fluid for the DCCD, wouldn't the 5mt's with DCCD need to have a cooler aswell?

I agree with Vikash. The only way this may be beneficial is for a high powered car that's being abused for an extended period of time. Volvo outdrives use GL5 also and they don't use a cooler. Granted, the case is surrounded by water, but a lot of them are attached to big big blocks also, and they can put some stress on things. Maybe it's a bad comparison since they only have one gear ratio, too, but I'll throw it out there anyway.

Steve

I'd be interested to see the 6 speed cooler setup, if there is one.

The gear oil does cool the gears, but how much extra cooling is necessary? On most cars, probably none. I agree that a cooler will only really make a difference if you drive your car very hard for long periods of time. If you are overloading the transaxle in short bursts, an oil cooler will make no difference.

The Porsche 944 Turbo (951) 5 speed manual transaxle (uncannily similar to a 2WD Subaru trans) had an external cooler loop with a gear pump driven off of one side of the differential. I looked for one to retrofit to my 944 but they're hard to find. I don't have the 951 service manual here but I'm pretty sure the pump is just a couple of plastic gears. I have also seen racing transaxles set up with an external oil pump belt driven off of a pulley attached to one of the inner CV joints. I would not worry about frothing the gear oil - it would be difficult to fit a pump capable of doing that under the car. You only need a small pump if any, because you're not trying to create pressure, just circulating the fluid.

If you know how the oil normally flows inside the trans case, you could just drill and tap holes in the right spots and hook up a cooler loop without a pump. Once it gets hot, the oil in a manual transmission really moves when you're driving, so there's plenty of existing flow to take advantage of.

Seems like a lot of work though. You could just change the gear oil more frequently to avoid the problems of oil breakdown, or switch to a synthetic oil if there is one that will work well with the synchros, as synthetics can handle much more heat than mineral oil.

I agree that if you're really curious you should buy a spare drain plug, drill and tap it and put in a cheap temp gauge. Although if it were my car, I'd just drain a small sample of the gear oil and look at it to see if it looks or smells horribly burned. btw - many gear oils smell much worse than engine oil, even when fresh. I've got some expensive GM synthetic ($18 a quart) for a 1 ton (and up) truck transmission that stinks like you wouldn't believe.

You could also set up some sheet metal ducting to direct more cool air towards the trans case (as that is what cools the trans anyway), although, again, I don't think it's necessary unless you're past the 300HP mark.

Sorry about the long post. I tend to write too much and badly at the end of the day.

I don't think oil normally "flows" inside the transmission at all. It just sits at the bottom and gears move through it.

vrg3 wrote:I don't think oil normally "flows" inside the transmission at all. It just sits at the bottom and gears move through it.

ditto

Also...you ever played with the gears at the auto parts store and watch the oil climb up the gears as you turn them? That's how the oil is being moved around.

vrg3 wrote:I don't think oil normally "flows" inside the transmission at all. It just sits at the bottom and gears move through it.

I've run a NP435 pickup truck transmission with the shift tower open, and I can tell you that even at idle in neutral, that oil is being thrown around by the gears. The gears act exactly like centrifugal pump impellers.

I was looking at the engine part manual the other day and saw that the 91 ss had an oil cooler...Does anyone know about these?

And then I saw this for sale on a certain JDM part site...

"JDM external Air-air oil cooler. fits all EJ motors (18/20/22/25) - all subarus have hte same oil filter. EARLS fittings, direct bolt on. You need to source a external oil filter setup (sandwich, lines, block for filter to spin on) - not that hard to come by. Add a greddy external filter adapter ($128) and you are set"

Would this be useful to pickup and would it help keep my tranny cool that likes to act up when it gets hot?

Thanks in advance for the info/insight.

Adam

On the 91 SS, the oil cooler circulates coolant from directly off the water pump through the sandwich adapter before the filter.

IronMonkeyL255 wrote:On the 91 SS, the oil cooler circulates coolant from directly off the water pump through the sandwich adapter before the filter.

That's engine oil. We're talking tranny oil

I don't think there's a need for a 5MT oil cooler either. If someone is abusing the thing enough to possibly break the tranny, I don't think cooling the oil will help much.

maybe for a road race car in some very long events a trans cooler would be good.
I can definitely notice a difference in how my car shifts once the trans gets hot.

Doh, thanks for clearing that up Subiluvr!

Ok, off topic then, any need for additional oil cooling with our cars? Should I pick up this part? PITA to install for the beni? What benis?

And on topic, yeah, don't want my tranny oil "cool" but when it gets hot it is noticably more touchy, grinding in second gear, the usual for these cars...Was thinking that along the lines of the smart guys above that it might be an easy work around. But obviously I'd need it spelled out for me since I don't seem to know where the heck my oils go, connect etc!

Cheers,

Try different fluid.

I had the 2nd gear crunch. I tried dino oil, two different types of sythetics, and then tried "Uncle Scotty's" cocktail.

It's one quart syncromesh, and I think something else, and the rest 75w90, or 80w90.

Check out nasioc for the exact details.

The cocktail was the only thing that has not ground, and I would definitely recommend it.

Good tip. I've tried a few things too but not that. I'll search it out. Thanks!

Anyone to chime in on the oil cooler? I'll let my fingers do the searching in general but if you have direct experience let me know.

S2000's have trans fluid pumps for circulation. It's gear driven off of the output shaft.

To keep from grinding, try 3 quarts of Redline Lightweight Shockproof, and 1 quart of Motul 75W90. Works really really well. If you still grind after using that stuff, you simply must have bad synchros.

With a PPG straight cut synchro gearset and 100% LWSP we were able to get the car into first gear from higher than 30mph. No revmatching or anything, just pushing into gear. Not a single grind. It performs about the same with the 3/1 mix.

I really doubt it would be worth it to have an external cooler for a manual trans.

The pump in the 6-speed is for circulation also, not necessarily cooling.

The oil pump is used to supply cooling, 6mt's in the US dont get the oil cooler though.

This thread is hella old too.

But what are you guys basing your lack of support for the 5mt cooler on?

Bac5.2...I was going to try this...Any opinion using this over your mix?

Uncle Scotty's Cocktail for Subi Tranis:

1qt Redline lightweight shockproof
1qt Pennzoil Synchromesh
2qt Castrol HypoyC 80w-90

Scotty's mix helps synchros because of the shockproof. The heavy weight oil keeps noise down, and the synchromesh is just a friction addative to help the shockproof.

I bet you'd have the exact same results using 2 quarts of shockproof and 2 quarts of 80w90. I bet you'd have synchros that work even better using 3 quarts of shockproof and one quart of Motul 75W90 to help keep things slinging around.

The US STi's oiling system is used for circulation. It may have a cooler overseas, but the US 6-speed has the pump and everything in the case, and it DOES pump when the trans is moving. A cooler could be plugged up to work, but I doubt you'd have significant gains.

We have a professional time-attack car that doesn't use a trans cooler, and it looks good. The ONLY oil temp problem that trans ever had, was using SHIT oil that sheared and blew the trans.

Sorry, there was supposed to be an "also" in that first sentance somewhere, it's used for circulation and cooling. US cars dont get a cooler they get a pipe that connects the feed to the return, but the circulation still cools the trans better than not having one at all.