400 stringer leaking oil when tilted up

Hey Gang. I'm new here and also new to boating. Last fall I purchased a 78 Silverline with a 120/400 stringer. Is there any chance that it may be normal to leak oil when the drive is tilted up? I had it apart last fall to put in a new impeller and felt that I did a pretty good job of getting it sealed back up. I normally have the drive in the down position, but went away for the weekend and left it tilted up. When I got home there was oil leaking but it is hard to tell from where. On the under side where the lower bolts on there are 2 small holes. It almost looks like that is where the oil is coming from. I'm hoping that this is just because I left it tilted up, but do you think I need to take it apart again?

Re: 400 stringer leaking oil when tilted up

You should not have any leakage at all. Clean it up really well and see if you can see where the leak is coming from.

Re: 400 stringer leaking oil when tilted up

Did you spill a bunch of oil when you put it back together that could be stuck in nooks and crannies that is making it's way out now? The joint between the upper & lower comes to mind - overflowed oil could have pooled there & now it's dripping out while tilted up.

Another thought - it's not coming from the tilt clutch housing on the port side is it? Those are netorious for leaking when the clutch shaft bushings wear and there's directional force on the tilt gear.

Re: 400 stringer leaking oil when tilted up

Pressure/vacuume test the upper and lower. The shift cable can leak if there is a separation in the cable also.

Re: 400 stringer leaking oil when tilted up

I cleaned everything up real good and tilted it back up. It is definetly leaking between the lower and the exhaust housing. I've only had the drive apart once and don't recall where the oil should be sealed. What I mean is, would my problem be as simple as having a poor seal between the lower and the exhaust housing or is the oil coming from somewhere else and leaking through that spot? I think that right behind that spot would be the shift housing. Is the shift housing submerged in oil?

Re: 400 stringer leaking oil when tilted up

I'm wondering if you're not leaking from your upper gear housing. Is your oil level in the upper gear housing going down? If you're leaking up there, it could be coming out between the upper and lower units. I can't think of an easy place to leak from off the top of my head and my boat isn't here at the house right now.

'74 is still an electric shift, I'm pretty sure, and that means the shift "stuff" is all down in the lower unit and should be full of Type C marine oil. But if your leak is coming between the lower unit and the exhaust housing, I think my attention would be turned to the upper gear case. If you disassembled the stern drive, and now you're tilting the drive up maybe check and make sure all of your retaining screws on the cover are tight and also double check the fill and level ports on the upper gear case (make sure those screws are tightened down).

Re: 400 stringer leaking oil when tilted up

any leak from the upper collects in the "tray" there and leaks out those holes
pressure/vacuum test is required

Re: 400 stringer leaking oil when tilted up

Thanks for your help guys. I'm trying to get an idea of what might need to be done before I take it apart. Just for the record it is a '78. After cleaning it up, it is definetly leaking from in between the lower and the exhaust housing. I guess maybe I will press/vac test before I take it apart. Do you know how much pressure and how many hg of vac I should test at?

Re: 400 stringer leaking oil when tilted up

stole this from a Volvo SX manual... I wouldn't go to 18 psi...10 plenty imo:
Attach a pressure tester (such as a Stevens S-34) to oil level hole, and pressurize drive to 3-5 PSI (20,7-34,5 kPa). Rotate propeller shaft and universal joint shaft to check sealing. If pressure loss is indicated, use a soapy water solution or submerge drive in water to find source. Make necessary repairs then repeat test. If pressure loss is not indicated, increase pressure to 16-18 PSI (110-124 kPa). Again, use a soapy water solution or submerge in water to find source if drive looses pressure. Make repairs as necessary and repeat test. Drive must hold pressure before making vacuum test, and must not loose more than 1 PSI (6,9 kPa) in 3 minutes. 2. 15 0 15 30 30 47119 Vacuum Testing 1. Attach a vacuum tester (such as a Stevens V-34) to oil level hole, and pull vacuum to 3-5 inches of mercury (10-16,8 kPa). Rotate propeller and universal joint shaft to check sealing. If drive does not hold vacuum, apply a heavy oil to seal and gasket surfaces to find source. Make necessary repairs then repeat test. No loss of vacuum should occur on low test. If vacuum loss is not indicated, increase vacuum to 14-16 inches of mercury (47-54 kPa). Again, apply heavy oil to find source if drive will not hold vacuum.

Re: 400 stringer leaking oil when tilted up

Thanks for the specs Howard. I'm hoping to take it apart and put back together tomorrow. Do you think I should be getting a seal kit or should I be ok with just silicone? What are good replacements for some of the items in the manual like:

OMC gasket sealing compound = ?
Permatex #2 = ? I looked at the store and did not see a #2
OMC high vis lube = 80/90 gear oil?

I did pick up some permatex ultra black gasket maker. All the packages seemed to say the same thing, but this one was the most expensive.

Re: 400 stringer leaking oil when tilted up

don't take it apart- you have to pressure test it before you disassemble anything. Once apart, there's no way to find the leak.

your upper might not need resealing - could be leaking at the $3 o-ring on the exhaust housing cover.
You won't know until you do the pressure test

the seals are pretty much all steel backed lip type seals- you replace them
a bit of sealant goes around the outer edge of the steel ring. so yes, seal kit - use all seals in the kit including the trucourse steering shaft seal.

Re: 400 stringer leaking oil when tilted up

I have not done the pressure test on the upper yet. I did do the lower. It did not hold and I could hear leakage from the hole in the front of the exhaust housing. I don't see that I can narrow it down any more untill I take it apart? I was thinking that I should be able to pressure test the lower again when it is removed. Do you think that it is possible to loosen the shift cable and just remove the lower gear case?

Re: 400 stringer leaking oil when tilted up

you need a manual

you can't pressure test the lower without removing the shift cable from the converter housing. A length of heater hose needs to be installed over the shift cable end with a bolt or dowel in the end to seal the cable. The cable unit is a breather vent for the lower unit. You'll never build any pressure- it's vented to atmosphere.

I thought we were talking upper...now it's lower? need a manual for that. Take the battery out of the boat before removing shift cables from the converter housing.

Re: 400 stringer leaking oil when tilted up

Thats an interesting post. I had wondered about venting yesterday when I pulled the drain plug the oil pretty much shot out of the hole. I'm now thinking that maybe my cable is not venting. Even though I was not doing the pressure test properly, I could definetly hear the air leaking down by the exhuast housing. Maybe I blew this leak because it was not venting and the pressure built up just sitting in the sun?


I do have a manual. Not sure how good it is, it is one that I downloaded. Maybe I have not read into it enough, but I have not yet seen anything about pressure testing or venting.