Sorry if I never actually posted the reason
I thought I'd written it, but I often end up deleting what I wrote and start over trying to sort of "edit things down" because I'm usually so bad at writing TOO much info.
Anyway, the reason I originally was going to use "Castrol 20w50" specifically, was that it had specifically been named on a page I found here at xweb.
Originally I simply did not understand enough about the "why" involved to make my own choice, so I had to look for something specific.
here is the page that I saw the castrol 20w50 mentioned:
http://xwebforums.com/wiki/index.php?title=Transmission#Gearbox_Oil
And here was the particular section (from that page) I got the info from:
"
Gearbox Oil
There are a number of recommended choices for gearbox lubrication:
- GL1 was the FIAT factory specification. It is still available, and if you just want to stick with the original recommendation, you can. However, lubricant technology has improved a fair amount in the intervening years, and many people are reporting better results with newer synthetics.
- RedLine MTL or MT90 is a well-regarded modern synthetic. Last I heard, Steve Hoelscher's warranty on rebuilt transmissions required that you use RedLine.
- Castrol 20w50 motor oil. This sounds wrong because the viscosity is all wrong, but motor oils use a different viscosity scale than gearbox oils, and in fact a 20w50 motor oil is about right."
As I said, I didn't know anything at the time about the "why" that was involved, so I didn't even know if another brand of 20w50 could be used or what.
So, it wasn't really that I was trying to "insist" on castrol specifically, rather, it was the only one I'd seen specifically mentioned at the time.
Plus I happened to have already bought one quart of it before I'd posted the original message.
The reason I posted wanting to know if the "regular motor oil" like the castrol could be added to the old style standard "stinky gear oil" was that I'd had the tranny start to drip while I was in the middle of something else.
Basically, I had my hands full at the time.
Literally.
As in, I was holding up the fuel tank trying to push it back up into the car when I suddenly felt something slippery on the far side of the tank (towards the center of the car).
When I smelled what had gotten on my fingers, it had *that smell* of old style gear oil. It's rather distinctive.
At that point I started looking all around for evidence of leakage, and saw that there were some drips coming off of a cable next to the tank (maybe the speedo cable?) and then when I looked above/behind me towards the back of the car (being on my back), I saw that the rail passing under the engine/trans looked wet with several dark drips hanging off of it.
Stuck my fingers up there, and it too smelled like old gear oil.
Lastly I noticed the shift linkage looked a little damp and/or shiney around the boot, but I'm not sure if it was actually wet or dripping, it just sort of stood out because very little is shiney under the car.
I was in the middle of a planned push to finish up several jobs that day. re-installing the fuel tank, reinstalling the fuel pump/filters, pulling the starter to clean/test/reinstall, and cleanup of the last of the electrical grounds and connections I'd seen that might be problematic, all in a big effort to reassemble enough to make another attempt at starting the car.
Since I already had so much on my plate I was loath to stop right in the middle of things unless it was absolutely necessary.
So, Since I already had one quart of 20w50, I thought maybe I could get by with that for the startup tests *if* it was compatible with what was already in the transaxle.
That was when I decided to run in and find out if it would cause a problem to add it in with the regular gear oil.
So I left the tank hanging halfway out of the car and ran in here.
spent a fair amount of time going in circles with my research and was getting nowhere, so I decided to just go ahead and make a quick post and ask if it would mix without a problem, figuring that if somebody happened to know, then maybe there would be an answer by the time I got the tank mounted, and if not, then I would either continue to reassemble the car or go back to looking up the answer myself.
I hadn't gotten to the point of looking up how to check the transmission oil level yet, because how much was still in there wouldn't really come into play until I'd gotten the car back together enough to attempt to start it.
I was projecting to be at that point some time in the evening, but the tank turned into such a pain I got way behind and didn't finish with the tank till after dark.
So I thought I needed the information in a bit of a hurry because I had such big plans for the day, but then it turned out that I didn't need the information so soon after all.
Also the wife's car started having a problem so I had to mess with it for a while, worked through the night on various things, but then my dad showed up the next morning and needed me to help do a marathon of yard work trailer loading for the dump etc which, combined with an accidental misjudgement with my blood sugar levels blew me out so bad within a couple of hours that I ended up pretty much useless for the next few days.
So the whole original need to *hurry* got completely blown out of the water fairly early on.
However, all of the additional information everyone sent ended up helping me to learn a lot of the "why" involved with the various oils being used in these boxes.
After all, when this started, I didn't even know what EP stood for, so I did not know how to avoid getting a fluid that contained it.
Anyway, I'm not sure if that directly answers your questions, but I thought maybe it'd be best just to go ahead and fill in more info about the whole situation that lead up to me asking if the fluid would mix in the first place.
