Re: How long does it take for Merc 150 HP outboard to pee after starting?
j_martin, I've been doing some searching (internet wide) for the last few hours and have found some folks who swear that slow pee is the norm for Mercs. Can't find anything that tells me why this should be so other than the "downstream of the thermostat" theory. You say 10 - 30 seconds but I've found several who think 4 or 5 minutes is reasonable. Guarantee if your impellers are not working for 4 or 5 minutes you will fry that motor. IMO, the pee stream exists to tell you your impellers are functioning, NOT to tell you your motor is up to temp.
I currently have 2 Mercury outboards - a 2001 60 hp 4 stroke and a 2003 9.9 4 stroke. If either of them took as long as 10 seconds to start peeing I wouldn't know because I would have already shut them down long before that and pulled them out for a tear down. I truly cannot imagine waiting 30 seconds for a pee stream. Don't have that kind of nerves. Apparently it takes a very brave man to own a 80's or 90's Merc.
To the OP:
1st) What year is your Merc?
2nd) If it's an 80's or 90's motor (which according to popular opinion can take minutes or days to start peeing), try REMOVING the thermostat and then run it. Following the popular theory, it should start peeing imediately. If not, I would say you have a problem.
Anyway, just my opinion, I could be wrong. /rant