How long can u run a sterndrive without water for cooling? I need to repair silent choice exhaust, but boat has not been in water yet this season, and is on trailer without access to a hose. All I need is to have it idle for a bout 15 seconds to test silent choice. Is that safe?

The engine will be fine for 15 seconds but it might smoke the sea pump impeller! Especially if there is no water in the pump at all!

fill a tupperware bin and drop the drive in it.

Why do you need to run it to repair? Make the repair and verify the flaps are closed by looking up the tail pipe with a light. But if you really feel the need to start, and your fuel pump IS NOT driven off the sea pump, just remove the belt to save your impeller and housing

+1 just did this last weekend when i found one my solenoids had come loose and was hanging.. bolted back down and after checked pipe with light.. had to adjust to fully close.

Simple system.. no need to fry your impellor..

I've read many times any run time on the impeller with no water equals busted impeller.

I can personally verify that is a true statement.

I used to run one of the blue Globe impellers, and those things were great. They used to claim that you could run those dry, and I believe them. That thing was run for years, frequently beached the boat in shallow water so I know I sucked up some sand and mud, and when I pulled it out, aside from taking a "set" on the blades, it looked perfect. I heard that they switched manufacturing plants at some point and were having problems with the hubs tearing out of them. I still have it, and if my stock Merc rubber one goes south, it might just go back in for more duty!

This.
Rebuilt a five horse for my dad.
Took a bucket full of water to the driveway and dropped the motor into it.
Test ran in it with water.

Doesn't take much. Sometimes just using what you have

Altermately, you can take the belt off the front of the motor if you're going to run it dry, then your impeller won't spin.. The serpentine belt is pretty easy to get on/off. just remember, you're running completely off the battery since your alternator will not be spinning either, so make sure you're charged up. Just did this yesterday on mine for diagnostics.