Lower Unit Leak Test

**Glastron1987** · 01-25-2020, 01:32 PM

What is a good spec to go by for leak testing a Mercury V6 LU. I have a gauge and bicycle pump setup ready to go. I'm thinking something like 5lbs for 10 seconds, but not sure.

Also, which seal is most likely to leak? I'm thinking the one on the prop shaft.

**Euroski** · 01-25-2020, 02:09 PM

I'm going to say PSI shouldn't drop at all over time?

**Davidlake** · 01-25-2020, 03:42 PM

It should hold 10 to 15 PSI for 15 seconds while moving the shift shaft front to back according to the Merc. manual.

**Beak Boater** · 01-25-2020, 04:12 PM

Its good to also test the gearcase under a vacuum as well. Gear case gets hot from running especially if your surfacing, then when you stop it cools down due to water temperature. That's when you can get some water incursion into the case as the cooling pulls the water into the case past any weak seals you may have.

**Glastron1987** · 01-25-2020, 07:52 PM

Originally Posted by Beak Boater

Its good to also test the gearcase under a vacuum as well. Gear case gets hot from running especially if your surfacing, then when you stop it cools down due to water temperature. That's when you can get some water incursion into the case as the cooling pulls the water into the case past any weak seals you may have.

What kind of tool is used for that?

**eli** · 01-25-2020, 09:18 PM

Pump it to 15 lbs turn prop shaft any change time for seals

**flabum1017** · 01-26-2020, 08:53 AM

https://www.amazon.com/Stevens-Instr.../dp/B005GY9X7Q

https://www.amazon.com/Stevens-Instr...omotive&sr=1-2

**InjectorService** · 01-26-2020, 09:41 AM

I've always done them at 15psi, turned all of the shafts, then left it for 5-10 minutes. If no drop, good to go.

**Dave Strong** · 01-26-2020, 02:28 PM

15psi if we can let them sit for at least an hour, also should hold 15" of vac.

Dave

**Glastron1987** · 01-27-2020, 09:57 PM

Well to start my rear one leaks. Doesn't hold anywhere near 15psi.

**Glastron1987** · 04-05-2020, 08:49 PM

Finally got this lower unit back together with new seals. The rear seams fine now, and the shift seals seem fine too, but the one under the pump seems to be leaking. I hear air escaping from that area when I pump it up and pressure doesn't hold. Is this normal at all. If not, what would be a fix? I cleaned the surface where the new oring seats as good as I could.