Water Pressure vs Water Temp gauge

[muddywater]

While I am nursing an epoxy fume headache to go with my fiberglass itch, I switching back to working on my motor for a bit. My 72' SF with 1980 Merc has a water pressure gauge. I can't seem to find another one (the old one is badly corroded) except for a couple teleflex ones that don't match my new gauges (Teleflex Heavy Duty Series). Have any of you ever switched to a water temperature gauge instead (these seem to be much more common)?. Could I just get the right sized electric sender and screw it in where the tube for the old water pressure gauge connected to the engine? I could get the old gauge restored, but it would cost as much as all of my other new gauges combined to do so.

Thanks!!
-Muddy

[Bigshrimpin]

You should have both.

water Pressure is important to run on a merc. If you have some type of obstruction you be able to see a big change in water pressure. for example if you have a bad impeller, pickup a plastic bag while running, or a thermostat gets stuck, or the poppet valve gets stuck open, or your motor get a steam pocket in block. H20 pressure gauge will show a big change in pressure, so you can avoid burning up the motor.

On my motor the temp gauge sensor is only installed on one of the heads, so water temp is not always super accurate.

[Old'sCool]

I'll double check but I think I have a Yamaha water pressure gauge you can have.

[Blue197320]

u need to have a water pressure gauge on that merc. bigshrimpin was helping me with a problem that i had/still have with my '84 200. turns out i needed to change a few things that some one put on the motor when they built it for me. without the water pressure gauge i never would have known that my poppet valve was stuck and i would have overheated that motor in no time. ive also got a temp gauge. dont know exactly how accurate it is but its there. i replaced the teleflex gauge with a quicksilver gauge because the guy at the boat store told me tha the merc sender and the teleflex gauge are not compatible. its funny cuz the new merc gauge looks just like the teleflex gauge....

[askipper3]

If you are running in the saltwater make sure to run freshwater through the engine.....it will travel up the gauge line and clean it out too. I had to use a air gun and blow mine out after a few months. It will read alot better.

[muddywater]

*grumble* *grumble* That is not what I wanted to hear. Oh well. I appreciate the advice anyway If I have to use one, I guess I will use the original 1970's gauge since that is the only one that comes close to matching my new gauges.

I had a thread over on THT about this motor. It supposedly has 20 hours and hadn't been run in 17 years. I had slapped in some new plugs, soaked in Marvel Mystery Oil, took it to the ramp and it fired up. The (possibly original) impeller disintegrated and melted part of the pump housing, all of which I replaced. It was running, albeit with gas shooting out of multiple orifices, so all the dry rotted gas lines have been replaced. I also replaced the stator since the wiring was gone. Do you guys think I will need to do anything to the poppet? I am just about set to take it back to the ramp if I can just figure out how to put the 70's throttle binnacle back together. I have already spent a couple days trying. I am close but haven't quite managed to sync the throttle and shift. Will said he had a newer Merc throttle I could have, but I don't think the newer ones use the same kind of cables???

[Blue197320]

i would change the poppet if i was u. mine was original from 1984 and i changed it simply because its pretty cheap insurance as it only cost like 20 dollars for EVERYTHING. maybe u should put new t-stats in as well. that throttle u are thinking about getting from Will might work. u will need to ask around a little more.

[Fr. Frank]

ABSOLUTELY change the poppet and thermostats!!!!
You need to change out ALL water lines/hoses as well, including the telltale hose (pisser)

If you're serious, temp gauges should be on each cylinder bank, with the sending units at the top. Keep the pressure gauge. Older pre-99 Merc V6's require 8 lbs of pressure at idle to prevent overheating and steamlock, and 18-40 lbs at WOT.

Muddy, any Mercury control box from from 1968 through 2002 will work. The Mercury cable system was unchanged throughout those years. FYI, All analog control boxes from 2003-2008 will work as well. You just can't use the digital SmartCraft controls.

[muddywater]

Please forgive my stupidity, but there is no thermostat or poppet in the Parts listings/diagrams. Would I be correct to assume that the "Check valve, bleed hose -upper", "hose, bleed", and "valve-check" correspond to a poppet and a "temperature switch assembly" is the aforementioned thermostat? Btw, it is an inline-6 not V-6.

Thanks much for the info on the cables and throttle.

-Muddy

[Blue197320]

fr.frank, if u do not mind i have to go against something u mentioned about the mercury water pressure. u said at WOT it should be at 18-40 psi. all the info i have heard that after the poppet opens (about 3k rpm) the pressure should drop to about 8-12 psi and stay there all the way thru WOT. maybe im wrong but that is what ive read on s&f and the local mechanic said the same thing. no disrespect at all.

ABSOLUTELY change the poppet and thermostats!!!!
You need to change out ALL water lines/hoses as well, including the telltale hose (pisser)

If you're serious, temp gauges should be on each cylinder bank, with the sending units at the top. Keep the pressure gauge. Older pre-99 Merc V6's require 8 lbs of pressure at idle to prevent overheating and steamlock, and 18-40 lbs at WOT.

Muddy, any Mercury control box from from 1968 through 2002 will work. The Mercury cable system was unchanged throughout those years. FYI, All analog control boxes from 2003-2008 will work as well. You just can't use the digital SmartCraft controls.