No and Low Water Pressure on 1998 Merc. 150 O.B.

[Jim Covington]

I have a 1998 Merc.150 carb.outboard that has not put up but 1.5/2.0 lbs of water press. when idling, and only 18 lbs at full throttle when it was brand new. I checked with the boat dealer about the low idling pressure, and was told that was normal. The pee hole water is so hot that I can't touch it but for a few seconds, and it has steam coming off of it. I have read the other comments about this on your page and see that this seems to be normal, but no one mentions how much water pressure they have. After two years I changed the water pump due to the pressure dropping down to 15 lbs at full throttle and the pressure came up to 22/23 lbs. Now it is four years old, pressure was down to 15 psig again, and I just changed the water pump again after I had the lower unit totally rebuilt after I hit a under water pipe. The water pressure has dropped from it's normal 1.5/2.0 to 0 psig at idle after 10 hrs. of use. I changed the poppet valve and spring, changed the thermostats, blew out all the hoses, flushed through the heads without the thermostats, washed through the block with the poppet valve out, and changed the water pump again. I haven't found a smoking gun to blame for still no pressure at idling. I also clamped off the hose coming from the top of the block down to the poppet valve, and the pressure came up to 12 psig. So does this mean that I'm loosing my pressure through the poppet valve, if so why? How much pressure/temp does it take to open this valve? Yes, I also checked my gauge against a new guage, blew out the pressure gauge hose, and checked for kinks in the hose...same results.<br /><br />Thanks for any and all help,<br />Jim Covington

 

[ODDD1]

Re: No and Low Water Pressure on 1998 Merc. 150 O.B.

Jim, what you are seeing may be normal, depends where you are measuring the pressure...the rubber hose that comes from the top of the block to the poppet cover is a water dump for cooling exhaust under the powerhead.....because the poppet end of it is pretty much an open dump, you wont build alot of pressure in this line. unfortunately, this is the line usually tapped into for a pressure guage. that being said, you do have a rather low pressure, maybe another leak inthe cooling system? a base gasket on the powerhead,water tube seals,poppet valve seat in block tight? rubber seal still in it? the output fiiting that your poppet valve hose hooks to, had it out of the block? debris it the fitting would show up like your symtoms....water pump service, have you changed base and upper housing too?

 

[sho305]

Re: No and Low Water Pressure on 1998 Merc. 150 O.B.

Better than my old '73 Merc at 5psi@2000rpm. And that is spec. Who needs no stinking thermostat?<br /><br />I can run it WOT for a while and when I stop the pee will be kinda hot, like hot shower warm is all. I like to check the exhaust water jacket for temps too; to show a problem. Not like I got a buzzer or anything. Water is barely warm when putting around.