mercury inline water pressure guage

[fishdog4449]

Hey there guys,
Fired up the engine to burn off fogging oil before i head to the lake on sunday. It ran great but my new water guage read ZIP, even at 1500rpm. I installed it per instructions (routed air line over powerhead) with a T from the block to the telltale and the guage, but do i have to block off the telltale completely for it to register the right pressure? The impeller is only a year old and it pumps ALOT of water, so I'm betting i did something wrong installing this thing. It was running on the muffs, but still should show pressure...Any ideas?
thanks!

 

[Chris1956]

Re: mercury inline water pressure guage

The inlines do not have much pressure. Maybe they get 15 PSI at WOT. Your motor is clearly pumping well. I would take it out and try it. See what the gauge shows.

 

[daveswaves]

Re: mercury inline water pressure guage

Does your block have the feed for the tell tale coming from the top of the block or mid ways by no 3.? Clearly you have lots of water, merc used a high volume water pump on the mid 70's in lines as opposed to high pressure in their newer engines. If your line feeds from the top and you tee in the gauge there you will not get a decent pressure reading at low RPM. I run the same engine and abandoned the idea of a pressure gauge for the same reason.

 

[fishdog4449]

Re: mercury inline water pressure guage

The telltale comes from the middle. I'm gonna take it out tomorrow so we'll see what happens.
thanks guys!

 

[Moody Blue]

Re: mercury inline water pressure guage

What pressure range gauge do you have, 0-15 or 0-30?

I just installed a 0-15 and will be trying it out for the first time tomorrow on a 71 Merc 800.

 

[76canaventure]

Re: mercury inline water pressure guage

Good Morning!
Idling on the muffs will barely lift the needle off the stop. I have a 0-15 on my '76 850, on the muffs it will read maybe 2 psi @ 2000 rpm with the hose wide open, in the water it shows that at idle. It's tapped in to the telltale mid block as well. At WOT (on a new impeller) on the lake I am getting 8. This style of WP seems to be able to pump huge volumes of water, just not big on pressure as others have stated.) Also speaks volumes about the limitations of muffs, that hose just can't get enough water in there at all. You probably have it installed right. Have fun on the water!

 

[fishdog4449]

Re: mercury inline water pressure guage

Thanks for all the responses guys!
Took it out on the lake yesterday, even at 5400 rpm the darned guage still read zero. I'm going to check the tube for blockage and try blocking off the telltale and see if that affects it. I'm not expecting 25psi, but SOME reading would be nice.

 

[HONKER1]

Re: mercury inline water pressure guage

Just curious. What would happen if you plugged off the tell tail tube. At 5 lbs you should be able to put your finger over the tube to see if the gauge will move. Maybe be you don't need both, gauge and a pee tube?

 

[AMD Rules]

Re: mercury inline water pressure guage

I suspect you'll find very little difference (if any) plugging off the telltale. End of the day, the inline water cavities are simply a free-flowing design and the small amount of water exiting the telltale is marginal in comparison to the flow through the motor itself. Hopefully you'll prove my hypothesis wrong. Please post your results.