Silly question? Water pressure help needed.

[ufm82]

My old girl is getting a new water pressure gauge this weekend for several reasons. I'm having overheat issues and the boat has never had one. I will be checking pressure once the gauge is in. My question is: When running an engine on a hose with muffs, does that impact the water pressure reading? Or will it give me a higher than normal pressure. My tap runs at 45psi. It seems I should know the answer but I can't get my brain to work.

 

[dlplost]

Re: Silly question? Water pressure help needed.

Yes a garden hose/muff can effect both the pressure and volume of water going thru the motor. It all depends on the waterpressure, fit of the muff and how far you open the valve on the hose.

I use a 55gal drum cut down instead of the muff. Pump in the motor provides all the press/volume so you know exactly what you've got.

 

[Mi duckdown]

Re: Silly question? Water pressure help needed.

When was the last time you changed the impellar?

 

[79Merc80]

Re: Silly question? Water pressure help needed.

What engine is this??

 

[ufm82]

Re: Silly question? Water pressure help needed.

1993 Merc 150 XRi. Impellor was changed 2 years ago and inspected last year. I'm of the impression that I have a blockage somewhere. I have an intermittant but persistent overheat issue that I am trying to fix. T-stats and poppet are new, water pump is good, blah, blah, blah. It doesn't do it all the time. Just when I don't want it to. LOL I have no gauge on mu boat so having one now will help pinpoint the issue. I have not gone the route yet of getting the infrared thermometer yet to check head temps, true water temp etc. My digital meat thermometer shows 145 when it's idling in my driveway on muffs. The gauge shows that as well. However when on the water it routinely runs at 175 and will sky the gauge if rpms are between 2,000 to 4,000. But not always...

I don't know if muffs will recreate the problem or not. Running in a barrel of water does not create the water pressure on the L/U. I have boatable water within 20 minutes of me but it would be much easier if I could do it in the driveway.

 

[j_martin]

Re: Silly question? Water pressure help needed.

My old girl is getting a new water pressure gauge this weekend for several reasons. I'm having overheat issues and the boat has never had one. I will be checking pressure once the gauge is in. My question is: When running an engine on a hose with muffs, does that impact the water pressure reading? Or will it give me a higher than normal pressure. My tap runs at 45psi. It seems I should know the answer but I can't get my brain to work.

The muffs spring away from the LU at about 2 psi, so they won't overpressure anything. They probably will not supply all the water the engine would want at high rpm's, so the pressure would be low. You're risking catastrophic runaway to rev it up high with no load anyway, so don't try it.

Should be able to see if pressure is normal at idle and off idle. You won't gain anything by setting up a drum. If you had a real test tank and test wheel (loads the motor) then you'd have something worthwhile.

See if it's normal at idle, then take it to a lake.

BTW, the impeller will take a set and lose efficiency over the winter. That's your problem. Check the water pump and change the impeller and any other parts that need changing. Look especially at the base plate and the inside top of the housing. Grooves are bad.

As a routine, check and/or change the LU lube each fall before storage, drop the LU and change the impeller in the spring.

hope it helps
John

 

[Mi duckdown]

Re: Silly question? Water pressure help needed.

Running in barrel is the worst, that water is to aerated.
muffs first than lake.

 

[CharlieB]

Re: Silly question? Water pressure help needed.

Double check timing and that the timing lever is moving well, not sticking or binding anywhere.