Hi all,
Im getting to the end on my project and i'm getting together the dash.
I have older Gaffrig gauges, and i try to plumb the water pressure gauge to my 502 Mag mpi Gen6. It is a mechanical gauge, so no sender, just hose directly to it.
Whats a good port for testing water press? The Tstat housing? I think this thread is 3/8 NPT right? What kind of hose should i run? ID?


Thanks so much,
Philipp

ports on intake up by the thermostat and use 1/4" line,,less likely to clog

Mine are plumbed into the drain plugs on the stbd side of each engine.

I apologize for not answering your question but pressure means nothing, flow is more important for cooling. Temp is the bottom line. You can very high pressure and overheat all day if there is no flow. And no, pressure does not equal flow to all those thinking they are the same.

Many run water pressure gauge to assess the state of the pump or impeller. For those that get into areas where sand or mud could be problem a pressure gauge will tell you pretty quickly if you sucked something up and damaged the impeller. I can see my pressure drop after 20 to 30 hours on an impeller. If i were to see had dropped much from the norm I would have an early warning of a damaged impeller and replacement is due. Just another tool.
To your original Q, either the block drain plug or intake manifold port fitting is fine. You can get a brass fitting with a 1/4" nipple for the intake. We used this line on my Son's boat as the gauge was already 1/4 NPT fitting. I like the clear so you can see if it has debris in the line. 1/4" black or red pneumatic tubing is cheaper but less flexible.
and plug for intake if you have this size block off plug

I had them coming off of the thermostat housing on my 502 MPIs.

What happens when you get it to the back of the gauge and have to step down to the smaller size tubing though?

I dont know, i took out the block port yesterday, the obe at the thermostat housing is so tight, i cant get it out. Block port thread i think should be 3/8 but i check tomorrow. I try to get a fitting 3/8 npt to 1/4 hose and route it to the gauge.

it will still read correctly. The changing of the surface area applies when you're designing something like a hydraulic jack.

Okay so the block port is 1/4 NPT. Bought a adapter and routed the hose to my gauge.