Water Pressure Readings?

[kyudizky]

I tried to utilize the search function but came up with nothing

can anyone tell me what water pressure should be reading when at idle and WOT for a '84 90HP Johnson (pushing a 17.5' stratos f/s bass boat). It runs right at 5000 rpm at WOT.

I watch the gauge often, but don't know what proper pressure should be to know if theres a problem.

Thanks

 

[Texasmark]

Re: Water Pressure Readings?

My Merc manual for semi-current engines in the 90 to 125 hp class specifies 10-15 psig @ 5250 rpm. I think I read somewhere that idle presssure was around 6 psig. Surely OMC is somewhere around there beins they are similar setups and cooling requirements are similar. Someone will jump in here and nail this for you.

Mark

 

[kyudizky]

Re: Water Pressure Readings?

Thats what I'm hoping, thanks Mark.

I looked in my seloc manual and couldn't this info in it, I'm sure its in the OEM manual.

 

[Fl_Richard]

Re: Water Pressure Readings?

Im not sure that the pressure number is the important part. I think the lack of pressure is what your looking for.

My 150 runs for 5-25 psi depending on speed. I suspect at those low pressures the guage is not very accurate. Use what you have and look for a drop from normal to clue you in to a potential problem.

 

[Vic.S]

Re: Water Pressure Readings?

Any change in reading could be significant. If it increases then it could indicate a restriction to the water flow somewhere after the point at which the gauge is connected. A fall in reading could indicate a restriction somewhere before the connection or a failing water pump.

 

[ezeke]

Re: Water Pressure Readings?

The water pressure on the V4 crossflow, if measured from the 1/8 id line leading to the overboard indicator, will usually run low at idle and in the range shown in the attached chart as the engine RPM approaches 5000.

The chart was published in 1997, so does not apply to more recent engines.

The important thing is that the operator can monitor the relative pressure from the helm, rather than having to watch the tell-tale.

 

[kyudizky]

Re: Water Pressure Readings?

Thanks, just what I was looking for.

I have the factory OMC 0-60 pressure guage. At idle, the needle barely moves, if any, and at WOT it is just a hair over 10. This concerned me, however, my tale-tell stream is solid throughout the rpm range, top to bottom. As suggested, i frequently eye the guage (all of them) basically looking for variation, since i wasn't sure what it was supposed to be around. I just wanted to make sure I wasn't starting out with to low of pressure to begin with. (First outboard, so learning daily)

So I seam to be a little on the low side, but since i've got a good pee stream and not overheating, i'll just keep watching for drops in pressure.

thanks for the help!

 

[R.Johnson]

Re: Water Pressure Readings?

It depend's on how the guage is mounted. If the guage is hooked into the tell-tale with a tee it will effect the quage reading as the tell-tale is bleeding off pressure. I used a 0-30# guage on my set-up as guages are more accurate at the high end of the scale. I hooked the guage hose directly into the block on top of the cylinder. It is a lot easier to keep an eye on the guage than the tell-tale. On many boat's you can't see the tell-tale from the driver's seat anyway.