I'm thinking about adding a "Low Water Pressure" warning light.

What would be the best location to mount the pressure sender? The body has a 1/8 NPT thread.

The easiest place is the top of the aluminum water neck at the front of the engine. It currently has metric threads, just drill out the German helicoil and tap to 1/8npt. ( be sure to check hood clearance if the sensor body is long... Greg F

Are you referring to the bleed screw? I wouldn't "screw" with that.

Karl

I was thinking that I did not want to be at a high point the system just in case an air bubble formed around the sensor and provided a FALSE reading.

There should be zero air at that point in the system when the car is running. The other way I have done it is to cut the lower radiator hose in half and fabricate an aluminum 1.5" tube with a sensor boss welded onto it. This is more work but will give you the most accurate water pressure reading. Greg

What diagnostic value/information do you gain from a water pressure gauge? Shouldn't it get to the psi relief value of the cap and then bleed off thru the overflow?

When the system loses (a lot of) coolant the pressure drops instantly. So it's a 'SHUT IT DOWN NOW FOOL' warning. If you pay attention and do (shut it down) it may just not get so hot as to destroy large expensive pieces. Or not.

That's right John B.

Low water pressure would indicate a problem with the cooling system faster than the water temp or oil temp gauge.

If the coolant problem is really catastrophic you MAY see the tremendous steam plume from underneath the hood. However, not ALL coolant issues are that catastrophic.

For less than $100 I am willing to try it a see what happens.

A new head gasket or new motor rebuild is a lot more than $100.

Hanging out in the air will fool a temp sensor but not a pressure sensor. While air is compressible and coolant is not; still the air (or steam) is at the same pressure as the liquid since they are both enclosed by the same container.

Also. There is a small block drain on the underside beneath the exhaust towards the rear. Don't know if it's enough clear to use for anything.

I like Greg's thing with the tube inserted into the hose.

No reason to mess up a perfectly good metric thread just to blow it up with a NPT. I hate NPT on a precision piece of machinery. An abomination against nature.

Thanks John. I never thought of it that way. I try to look at gauges every time I cross start finish but I see your point. I routed my overflow from the reservoir to blow on the windshield to let me know when the system is over pressurized if Mr. Headgasket decides to go south. I may try to hook up a warning light.