Outdrive bottle cap vent question
 

When I was building everything in my boat, I decided I wanted/needed a bigger drive oil reservoir and instead of buying a high dollar one I made one out of stainless pipe with the ends capped and welded in a bung/cap at the top. My question is...I went with a vented cap with no check valve in it and noticed that when running hard it would push oil out of the cap vent. Am I on the right track thinking that I need some kind of check valve in the cap so that it will build pressure in the drive and let air in when needed but not push oil/air out when running? Would like to figure it out before I get it back on the water to prevent a mess. Thanks!

YOu need a bigger expansion tank.
Check valve that isn`t going to allow any expansion? What`s the point in having an "expansion" tank then lol
If the pressure can`t expand it will make it`s way out alright , probably thru a seal somewhere .

Makes sense and that's how I always thought of it but then I remembered the regular bravo bottles had a rubber nipple deal in the cap that I think is supposed to act as a check valve to let air in and let the fluid go in the drive but not the other way....I modeled my tank after the one imco sells for my drive but apparently I didn't go big enough....great something else to redo hahahaha

Regular Bravo drive lube bottles use a cap just like you describe with a one way valve that allows air in, but stops air and gear lube from going out. Pressure does build a little in them, but that is why they only get filled about 2/3 full. The level in my gear lube moves up about 1/2" when the drives are warmed up.

That's about all mine would move when it was a bravo...now with the SCX upper it moves a lot...5" diameter reservoir and it will raise an honest 2-3" if I'm running hard and 1-2" just normal cruising around. If I keep the level barely visible in the sight glass I can usually get away without an over flow but anything higher and it spits fluid out when I'm gettin after it.

I did not know that about Bravos expansion tanks, the drives dont hold much fluid so maybe thats why they get away with it...
Wet 6s will fill up this entire thing after a hard run.. but drives also hold 5 gallons each.If I could check valve em that be fantastic but I`m afraid to .


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Us poor bravo guys can't afford all that damn fluid Dan! hahahaha

Like griff mentioned they are designed to build a little pressure which I think is designed to help keep water out if I'm not mistaken so brings me back to my original question if I should get rid of the vent and do a check valve? The way it is now the drive can't build any pressure because it's just vented off and I'm wondering if I'm setting myself up for failure not having it build pressure?

I don't think the not having pressure affects anything negatively. The check valve cap is mainly to keep the lube from escaping.

How do you know how full you reservoir is being that you said it was made from SS pipe??? Did you put an Merc alarm in it??

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I welded some stainless fittings in and put clear tuning in as a sight glass....I have to keep it barely in the sight glass so 1-2" of fluid in it or else it pushes it out of the cap which has a small vent hole in the cap. It has a strainer/filter on the underside of the cap that I think is to keep fluid in but it clearly doesn't work hahaha

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This is the cap kit I welded in

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 .:ernaehrung004:

How much oil does a IMCO hold ?

Thanks! If I remember right...the imco holds about 3/4-1 quart. I basically modeled mine off of theirs in a way so the capacities should be damn near the same....that's why I was confused when this started happening....I don't know if they have a check valve in the cap or if it is just vented. Suppose I could call and ask lol. I'm kinda leaning towards a clear one like yours...would let me see oil all the way to the bottle instead of having to have it almost 1/4 full before I can see oil. I have like 30-40 bucks in this one and a little time so not a huge deal If I have to change it. I'm thinking that on a stock bravo this would work great just maybe doesn't have enough room in it with having 1000 HP in front of a SCX hahahaha