Mercruiser 3.0 spitting water!

Joined
Jul 6, 2019
Messages
6
So I just got this 86 searay Seville with a mercruiser 140/3.0, guy said it ran last fall but during seasonal maintenance the mechanic found a blown head gasket. He didnt want to touch it anymore so sold it cheap. After inspecting block, head, and cylinder walls it didnt appear to have any damage or warping, got it all back together and it ran fine... UNTIL.. the thermostat opens, then it shoots water out of the valve cover hose, at like gallons per minute rate. My question is, do I have a warped/cracked head, bad gasket. Or cracked block? Still has good oil pressure, temp, and runs fine even when water comes, although I stop it immediately of coarse. New ignition system, gaskets, and oil/filter. Are cracked heads common or warped more likely? How about block? Any other possibilities? Thanks in advance.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Hi
you mean water comes out the breather going from rocker cover to air cleaner ??
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,092
Your description makes no sense, thermostat has no bearing on flow into the valve cover area. Water can only exit there when the crankcase i filled with water to the top of the head. Would not even be oil ,more like a vanilla shake
 
Joined
Jul 6, 2019
Messages
6
Yes, the first time it happened out on the water it looked like vanilla shake. I suppose your right about the thermostat, I just assumed once it hit running temp and the thermostat opened it is circulating more water through the block/head and that's when it becomes noticable? Not sure but the second time while running on muffs after another oil change it was clear as day. Water without oil mixed in it yet so it seems pretty sudden. It sat for a while but a clog seems highly unlikely hence my original guesses.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
pressure test the cooling water jacket

most likely there is a crack in the block on the inside just above the pan rail on the port side.
 
Joined
Jul 6, 2019
Messages
6
So after disassembly we found it literally broke a rocket arm off... like sheared the iron.. that'll do it huh!? Lol I suppose we should inspect crankshaft and block very closely to make sure theres no other issues. It was a sticky valve but had started moving back and forth fine. I thought it had just sat too long guess I should have brought it in for a valve job...
 
Joined
Jul 6, 2019
Messages
6
Also how do you go about pressure testing the water jacket? I've never done anything like that before. I'm pretty mechanically inclined but it's my first boat.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
with the block drained
take the line from the thermostat housing to the exhaust manifold and block off
take the line from the transom shield to the thermostat housing and install pressure gauge and a means to pressureize.
pump to 15psi
it should hold 15 psi for hours

if its not holding pressure, listen for the hiss

if its coming from the valve cover, you have a cracked block
 
Joined
Jul 6, 2019
Messages
6
Ok thank you! I'll have to check it and get back to you guys. I gotta get a new head first. I got a good lead on a motor.
 
Top