coolant pressure switch

[guymandude]

Is anyone using a coolant pressure switch in place of bi-metal temperature switch on an E36 or maybe E46? My car is an E36 euro M3. I switch the fan manually and I would like to add an early warning coolant loss light, something that will come on before the coolant level switch and a brighter light I can mount in my field of vision. I was able to find some posts about using a pressure switch on E30's but it seems that their radiator sees a low/no operating pressure or static pressure at the inlet side so radiator mounted pressure switches might not work for E30. Is E36 different? does anyone know the operating/static pressure on the inlet side of the radiator for E36 or where I would look for this information. I could set up a Test port and verify however the car is in pieces and I would like to finalize this job before pulling the car out for next season.

what kind of switch are you using and how are you grounding it?

I feel like the simplest, least evasive, solution for me would be to tap a brass radiator plug for the 1/8 NPTF 3psi switch and use a second ground wire to chassis from the body of the switch since the radiator is isolated with rubber mounts.

[aeronaut]

Does low coolant pressure, by itself, provide useful information about the health of the system?

[guymandude]

I'm trying to add an early warning for any leak. Hose blowing off, end tank crank, rock in radiator should all drop the static pressure to 0 almost immediately and I would get a warning light which would be placed in line of sight. That way I know to shut it down and save the engine.

[gdavid]

I have thought of installing a cooling system pressure gauge, a spike in pressure would warn you that you are about to blow a hose or expansion tank apart and no pressure would let you know it has already happened prior to overheating. I don't know about the euro S50, but on the US version, the early cylinder heads had three threaded holes (the later castings only had 2) into the water jacket, OBDI cars used 2 temp sensors and the third is connected to a preheat circuit to the throttle body (the OBDII cars use only 1 temp sensor and either cap or don't have a third hole). This is a pretty useless feature in all but the coldest environments and a no-brainer to cap it off on the other end of the circuit and install a sending unit for pressure.

[Franky goes]

If you install a pressure gauge on the head itself it will not survive the vibration.
I installed mine on the small line feeding the throttle body.
Can report on it as it stopped working a couple of days after install and have been busy getting the engine to run so I have not taken the time to trouble shoot yet.
I'm using a setup from Longacre.

[gdavid]

Then how does an oil pressure sending unit survive?

[NeilM]

Then how does an oil pressure sending unit survive?

Well, it is generally recommended to remote mount them. That said, for several years I ran my VDO oil pressure sender direct mounted, with no problem at all, until getting around to doing a remote mount.

Neil

[olemiss540]

My 73 vw has a pressure switch on the master that activates the brake lights when pressure is detected. I am sure you could rig up something with some OTS pressure switch to do the opposite?

[ScotcH]

We had one mounted in our system, at the tank return line. It was used when we were chasing water pressure issues (ie, headgasket pressurizing the system). Worked well, and when logged we could see exactly what was going on. I guess going the other way (low pressure) could also trigger an alarm.