doug928

I remember reading in an old post about problems with A/T's in which the fluid level changes when hot to cold due to movement of fluid between the tranny pan and the converter. Could anyone elaborate on this problem and does anyone have a fix? It seems to me that my tranny fluid level when the car is cold is near the MIN fill level. After initial startup it falls to the very bottom of the plastic fill tank. After some warm up the level is still below the MIN level in the tank. I did a fluid change in Feb and had the levels set properly and I've noticed a steady leak (as noted in a previous post) from the passanger sie of the pan. I believe that when I fill the level correctly and after the car sits for a few days, the fluid backs up and overfills the pan and leaks. Does this make sense to anyone? can this be fixed? I believe this might be part of my leaking tranny fluid problem.

BrianG

Doug, I think (hope) that you are experiencing the same issue that I am with my '86 car. Immediately following a "Porsche Specialist's" spring servicing of my car, including transmission fluid and filter, I noted an ATF leakage spot where I parked. I had never seen this problem before the service, but must aslo admit to never having checked the ATF level before, since I had owned it only a few months.


Investigation reveals that the leak is, in fact, coming from the right (pax) side of the transmission pan-gasket. If you look closely, with a bright light, after cleaning/drying the area with brake-cleaner, you can see the gasket start to ooze at the gasket-case (not gasket-pan) interface. When clean and dry and filled to the mid point on the reservior window, (engine running in neutral after cycling through the gears a time or two), there is NO leaking noted with the engine off. With the engine running in neutral oozing begins at the front right outside edge of the gasket. Oil level remains constant.

Since the reservoir is sealed to the oil pan, overflow into the pan SHOULD simultaneously back up into the reservoir and leak out the filler cap (if it's on). This is NOT the case on mine, even if I leave the filler cap off all together, running or not.

I have replaced that gasket 4 times, noting little difference in leakage. I have altered the torque of the 6 pan-bolts.... 5 in.lb in either direction makes no difference, while 10 in.lb in either direction increases the leakage rate substantially.

I have examined the oil pan closely and can see no evidence of damage or deformity.... and that thing is stamped from some PRETTY SUBSTANTIAL material.... so a trival force would NOT result in even a subtle deformity. The only "questionable" result of the examination is that the pan's gasket surface, at the inner-most portion of the "center bolt arc", shows slightly higher than level with the front/rear straight-edge check. This is a confounding finding since the case's mating face is pretty obviously machined FLAT. The thing is, there is NO way to deform the pan in that manner, the way it is made.

I'm about 6 seconds from using some sort of gasket sealer on the darned thing. I'd never use any "scilicone type" material because of the contamination issue, but I'm tempted to use a non-hardening product like Yama-bond. I hope you have a better solution, or can discover another possible reason for the leakage.

I know these things........
..the leak IS at the gasket/case interface....
..it's not a back-flow issue (on my car at least) because the reservoir never overflows
..it's not an "internal pressurization" issue because that would overflow the reservoir, also
..it's not a common issue becasue the "usual suspects" haven't piped up to address this issue on my previous posts.
..it's not the front seal..the TC is clean and dry and so is the case, up there
..it's not the vac-modulator or the TV cable or the shifter-shaft seals because you can see them not leak as the ooze begins to show on the pan gasket
..it's not the transmission cooler lines or joints becasue you can see them not leaking, too.

Are these findings consistent with yours??

mpesik

All in all ,take your car to a Doctor, I believe your car has a case of Gonneria! Perhaps the Voodo Spirits could help!........WIERD!

Erik - Denmark

Doug,
Look carefully at ATF reservoir, and you will find a rough temperature level indicator
When checkeing, the engine shall run and the gear handle placed in N
That's natural that the level is higher when the ATF oil is warm, therefore better to check the level when the oil is warm
Check the users manual, as I remember there is a good instruction and picture
Regards from Erik in Denmark

doug928

Brian,

I'm in agreement with you this seems to be some mysterious gremlin. Let me know if you use a sealer on the gasket and if it helps. Erik - I have checked the fluid levels properly - and when the engine is hot and in neutral the level should be at the Max line and it is not ( It was when I first did my tranny fluid change but over time as I lose fluid it is falling). I do remember an old post which someone referenced something about fluid transfer between the pan and the converter that shouldn't occur but can in some instances and I thought that this might be happening in my case causing the fluid level to rise in the pan because when the car is shut off the fluid in the converter (which should remain there) flows back into the pan. Brian have you noticed this with your transmision?

Erik - Denmark

Dough,
1. No you have not checked properly
That have to be done at idle, hot and in neutral, if not full here ad oil until the mark(s) - you have more than one marks to be used according to the actual temperature
2. When you then stop the engine the level will increase and cannot be used for anything
That is due the converter, and is normal for all automatic gearboxes
Check, fill - up at idle until until the level is between the max. and min min. depending of the oil temperature
See your Users Manual

Regards from Erik in Denmark

doug928

Eric,

Yes I am aware of this procedure and this is how I measured the fluid level - and due to my leak is too low! I'm more concerned with the cause of the drip and trying to find a cure.

Doug

Erik - Denmark

Dough,
Where do you have the drip?
You will typically get leak from the pan if the screws is tighten too hard - As I remember, they shall only be tighten to 8 Nm
Erik in Denmark

BrianG

Doug, the on other thing you want to check, if the leak isn't consistent with the amount of fluid loss, is the possibility of leakage in the cooling system. The cooler lines consist of 4 pieces, with a joint about mid-way, up in the torque-tube tunnel, along with the joints at the transmission and at the radiator. The trickiesst defect to detect is a heat-exchanger leak inside the radiator. Apparently it's not that uncommon.

I'd loosen the rad's drain plug and run the engine until warm, then drain a bunch of antifreze through a white towel of piece of sheet. The ATF's red color should be apparent if it's in there contaminating the coolant.

This isn't my problem because the driveway has the tell-tale stain of a cup of ATF per day!!!

doug928

Brian,

I don't think I have a leak in the cooler lines. I recently drained the radiator and flushed it out and there was no evidence of any problem or discoloration in the rad fluid. I may consider over the winter of dropping the transmission. I have to give this some thought though because I had other projects planned instead - i.e, new motor mounts and new interior carpet.

BrianG

Doug, I'd appreciate your thoughts, because this issue has ruined my 928 season this year, for fear of creating some transmission damage. I think I'll try the gasket sealant, because even Mark over at Devek suggested that this gasket leak can be a stinker to solve. I'm not willing to buy a $600.00 Can oil pan just to find out that the pan wasn't the issue!

doug928

Brian,

I understand you fustration. I am going to drop the exhaust and remove the heat shields and take a look at the transmission lines which run over the TT. I just noticed a little wetness as I was peaking around the underside looking for my tranny leak. When you did your other transmission fluid changes, did you ever notice the overflow tube coming off the plastic tank? I was wondering if some of the problem might be caused by a crack or improper seal between the tube and tank, and when the fluid gets hot and expands(?) , if the tube was incorrectly seated it would allow fluid to come out.
Another observation:
As I was reading the WSM's, it clearly states that when cold (temp between 20 - 30 deg C) the fluid level after the car has idled for a couple of minutes, run through each gear and set in N the level should be at the bottom mark on the tank - 20* (pg 38-2, 38-3) Part of my problem (may be yours also?) seems to be that when I achieve this reading, after the engine is shut off and sits idle the tank backs up to the top of the fill cap and since any fluid will always be level with itself, that means the level in the pan is also over the top of the gasket - thus exerting some (although minor) pressure on the gasket. If the gasket has even a slight unevenness in its surface the pressure of the fliud on the gasket might cause some fluid to escape at the weak point. I was wondering why my tank backs up with fluid this much? This doesn't seam right and I have been trying to figure out why. i thought if I could solve this problem I might be able to also solve the leaking fluid problem also.

Sorry for the rambling - I hope I made sense. Let me know what you do.

Doug

SharkSkin

I've seen this "overflows when sitting overnight" issue on other automatics. Usually what it amounts to is that due to this seal or that having a leak, usually internally, air gets into the system where if all was well it wouldn't, or a check valve designed to prevent this doesn't seat. For example, if air can get into the torque converter then the fluid will drain out into the body of the transmission. Auto trannies are designed to pump fluid into all of the internal spaces and keep it there. Did you ever find crud in the pan? It may be time to at least clean out the valve body.

BTW, I'm approaching this from an understanding of hydraulics, and a shaky grasp of how auto trannies work... but I have no expertise in this area other than pulling valve bodies on domestics to do "shift kit" mods. So I won't be able to give you specific help with identifying the exact cause, but I can tell you that this sort of thing is not unheard of in autoboxes with mileage in the triple digits.

HTH

BrianG

I have noted the over-fill situation when the engine stops, and I assumed that the top 1/2 of the T/C emptied back into the system. This is certainly a possibility in terms of an "over-night" puddle if the reservoir's vent line were not securely in place. BUT that's not my problem, since I can see the ooze from the gasket-case interface.

I too have been extra-ordinarily careful in the filling of the ATF and think that that is not the issue at hand, either, since I continue to get a puddle forming when the reservoir shows something in the way of only 1/2 full........ that's WAY below the cold-fill-line.

I've had it with this issue so, against most recommendations, I resorted to a gasket sealer. I used an old reliable product that has a broad following in the whole of the motorcycle realm. The stuff is called Yama-bond. Obviously it's a Yamaha stamped product of uncertain actual manufacture. It is particularly well respected for it's void-filling and it's longevity properties in very inhospitable environments, like aircooled high performance motorcycle engines. It is particularly relied upon in the situation where there is a persistent leak where there is a metal-to-metal interface with NO gasket called for. It's sticky and thick with no tendency to run. It skins over to become non-attracting to dirt. It doesn't solidify, so you don't get breakaway bits circulating in the lubricant. It disassembles with some slight adhesion of parts, but residue cleans up easaily with isopropyl alcohol. And that means it's impervious to mineral lubricants, so it'll stay in place.

I skinned the apex of the convex surface of the pan's gasket mating face, and skinned the ridged face of the gasket. I also thinly skinned the case face with just a finger-smear of the stuff to assure a good bond. I mounted the pan this evening, and will let it set to skin over, overnight, and then fill the thing with ATF in the morning.

WISH ME LUCK!!

SharkSkin

WTG Brian... if that doesn't do the trick, just weld the damn pan on.