I suspect with that set up you're going to see a significant amount of oil being pushed out of the drive into the resv anytime your running hard for any length of time. If you remove the rubber gasket inside of the merc resv cap and then run it hard the bottle will slowly fill up and overflow. I found this out the fun way.

Do you think I should run a bigger bottle still with a vented cap or put a check valve in to essentially make it a bigger metal version of a merc bottle??

Thanks

How full were you running the reservoir when they blew out?
Your fabbed reservoir appears large.
Maybe just play with various levels and see where the lube jumps around.
Seems given enough "expansion volume" even with a vented cap you'd be alright.

Filling the drive from the bottom until the lube just reaches the reservoir as per Mercs procedure.
It's not like your drive is going to be low on lube with nary any in the bottle.
IMO Mercs in bilge drive reservoirs are pretty much just a failsafe to alert of an unnoticed leak or issue.
They aren't really an ease of maintenance ordeal where you can drain your drives and then just refill right in the bilge.

I mentioned earlier that I always kept it as low as possible once this started...just so it was visible in the sight glass so I knew something was in there...I would guess that it will puke 1/2 quart or a little more into the bottle when I'm running hard...it will suck it back down in a matter of minutes when I slow down but eventually it will spit it out of the cap enough that when it sucks it back down it's out of the sight glass and I have to add more and the cycle repeats.

I understand that this is basically a gauge in a way that it only shows that the drive has fluid in it but it is one of my "checks" when I'm going out or while I'm running every once in awhile and would like to be able to keep it in the sight glass if possible?

Nice reservoir. Very similar to Marine Machine hyd steering reservoir.
If the level is fluctuating that much, I would swap to a check valve cap.
Maybe try to find a male to male adapter you could screw in and run a Mercruiser cap??

I was thinking I could just drill the cap out and find a small check valve and weld it in flush...worst case I have to buy a new cap hahaha

After seeing Dan's setup he posted, I'm thinking maybe switch to an all clear reservoir that way I can run it lower too and still see that there is fluid in it? I know it's how merc designed their bottle but I'm a little worried about the pressure build up in the SCX. That thing was too damn expensive to chance blowing seals out lol. Maybe I should thread the cap and throw a gauge in it for a run just to see how much pressure it's actually building...if it's only a couple pounds I wouldn't think it would affect the seals?

Have you checked with IMCO on their thoughts?

Just out of curiosity, what drive oil are you running?

I have not checked with IMCO..in the past when I've called them all I've gotten was a sales pitch and no real help..could have just been the person I got at the time but since I don't have their bottle I figured all I would get was told to buy their bottle hahaha

I am running royal purple max 75-90 with a little bit of pro long engine treatment mixed in per Dick(mr gadgets) who built my lower. SCX upper with sportmaster -2 lower.

You did a nice job on your expansion bottle .

How much oil does a IMCO hold ?