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Author Topic:   Proper Water Pressure Guage Readings
Perry posted 01-10-2004 10:42 PM ET (US)   Profile for Perry   Send Email to Perry  
I plan on installing a water pressure guage on my 2002 Honda 90. It has less than 100 hours on a new impeller. [What is the proper pressure indication] at idle and WOT?
jimh posted 01-10-2004 11:44 PM ET (US)     Profile for jimh  Send Email to jimh     
I would consult your owner's manual for advice, or contact a Honda authorized mechanic. Pressure indications tend to vary with different engines and manufacturers depending on where the gauge is tapped into the cooling system.
Perry posted 01-11-2004 12:40 PM ET (US)     Profile for Perry  Send Email to Perry     
My owner's manual has no information regarding water pressure readings. I guess I'll call the local Honda dealer and speak to a mechanic there.
simonmeridew posted 01-12-2004 07:31 PM ET (US)     Profile for simonmeridew  Send Email to simonmeridew     
The problem with giving you a hard and fast answer is that the pressure reading at the guage will vary depending on the type, brand, and size of motor. It will also vary with the type of installation you have done, i.e.: where on the motor you are measuring the pressure.

With some brands of motors you would tee into the [confidence stream outlet] hose, in other brands the [confidence stream outlet hose] is under very little pressure and would not make for a meaningful pressure reading.
My Johnson 70 2-cycle had a plug in the water chamber casting. My owner's manual directed me to take out the plug and connect the water pressure fitting to this threaded hole; my pressure guage shows about 12 PSI at idle and 28 PSI or so at WOT. The guage maxes out at 30-PSI. There's no way there's 28 PSI at the [confidence stream outlet hose] even though it's a good strong stream: 28 PSI will squirt across the yard and then some. If I had connected to this [confidence stream] hose I would have gotten a very low reading. So you need to consult your dealer to get the right guage (0-30, or 0-60 PSI) and the right mounting point for the sender system on the motor.

jimh posted 01-12-2004 11:44 PM ET (US)     Profile for jimh  Send Email to jimh     
I think also the point at which the confidence stream is taken off of the water jacket also varies among brands of engines. Some engines, like Mercury for example, provide the confidence stream outlet at the end of the cooling system, so that water coming out the confidence stream outlet has passed through the engine water jacket. This is usually easy to see because it will be warm water and the pressure is not too high. The stream will also not appear immediately on start up of the engine.

Other brands take the confidence stream connection right off the water pump, before the water goes through the cooling jacket of the engine. This is usually a higher pressure point, and the stream appears as soon as the engine starts. The water coming out is not warmed by the engine.

As Simon explained, where the gauge tap is installed will affect the pressure it sees.

By the way, many OMC engines seems to produce a huge volume of water from the confidence stream, particularly on the big V-6 engines.

Perry posted 01-13-2004 02:14 AM ET (US)     Profile for Perry  Send Email to Perry     
Lots of good info guys. My boat goes to the dealer next week for some warranty repair (small cracks in gellcoat near transom). When it is there I'll ask a mechanic where to put the water pressure fitting and the proper readings at idle, cruise and wot.

Jim, as for where the confidence stream is connected, my stream appears right when the motor is started, has plenty of pressure and does get warm after a few minutes. This makes me wonder weather it passes through the engine water jacket or right off the water pump. I will ask the tech when I'm at the dealership next week.

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