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Water pressure switch

rb92673

rb92673

racecar
Joined
Jan 17, 2017
Location
San Clemente
I want to install a pressure switch, like the oil pressure switch for the dash idiot gauge, into my cooling system. That way if I have a coolant leak during a race and idiot light will light up on the dash and potentially save me an engine.

Any suggestions on where to plumb one in? Are there extra ports on the head or block?

B230FT, '85ish 745
 
Why not consider something like the 960 coolant reservoir? Those cars have a low coolant warning light in the later model cars. From what I understand the sensor is in the coolant tank and you can adapt that reservoir to an older model.
 
dl242gt said:
Why not consider something like the 960 coolant reservoir? Those cars have a low coolant warning light in the later model cars. From what I understand the sensor is in the coolant tank and you can adapt that reservoir to an older model.
Click to expand...

Thanks. I like that idea.
 
The pressure switch is a nice idea, though. It will give you the fastest indication of trouble, especially if it springs a pinhole leak. On the other hand, if it's a pinhole, you don't necessarily want to cancel a race because of it.

Obvious solution: use both! Then you'll know pretty darn quick if there's a leak and the magnitude of it.

Situational Awareness. :nod:
 
I have a switch like this on my lemons car. Works great. We lost an engine previously when we had a hose blow. By the time the temp gauge showed hot it was too late and we lost the engine. I think the coolant reservoir level switch would work as well though. That car doesn't have a coolant res. Wish it did!
 
Toybox said:
The pressure switch is a nice idea, though. It will give you the fastest indication of trouble, especially if it springs a pinhole leak. On the other hand, if it's a pinhole, you don't necessarily want to cancel a race because of it.

Obvious solution: use both! Then you'll know pretty darn quick if there's a leak and the magnitude of it.

Situational Awareness. :nod:
Click to expand...

I like the idea of idiot light overkill. I'd probably wire both to the same light.

arsenix said:
I have a switch like this on my lemons car. Works great. We lost an engine previously when we had a hose blow. By the time the temp gauge showed hot it was too late and we lost the engine. I think the coolant reservoir level switch would work as well though. That car doesn't have a coolant res. Wish it did!
Click to expand...

I have heard this same scenario so many times. Nobody ever looks at the temp gauge.

Any obvious places on the block I can add a pressure switch? Maybe the drain?
 
You could use a fuel pressure gauge [0-15lbs] tied into any where in the system.
 
rb92673 said:
I like the idea of idiot light overkill. I'd probably wire both to the same light.


I have heard this same scenario so many times. Nobody ever looks at the temp gauge.

Any obvious places on the block I can add a pressure switch? Maybe the drain?
Click to expand...


I don't know what the thread is and it lives under the turbo but there is that block drain on the right hand side. That's where my water cooled oil cooler from a 940 is plumbed in.
 
My 745 has long since departed from my ownership; but, I thought the block drain was an NPT thread (1/8??) which should accommodate a large number of senders or switches. You could direct mount or mount remotely.

Stewart Warner makes a 5000 series of switches which are available in a large range of settings (both NO and NC).

https://www.stewartwarner.com/produ...itches/?fwp_type_2_checkboxes=pressure-switch

They also make senders. There are lots of other vendors of switches and senders if you go to a place like DigiKey or Mouser.

The biggest problem with a switch that goes closed when the pressure drops is that the cooling system is at atmospheric pressure when you do a cold start. As soon as you start the car you are going to get an alarm which stays on until it heats up and builds pressure. That is probably OK for a race car; but, perhaps an annoyance for a daily driver. The fluid level monitor in the tank eliminates that problem; but, with an aluminum head by the time the tank level drops to the alarm level it might be too late. You can make the pressure switch work if you condition the alarm with a temperature switch or sensor. The simplest arrangement would be to put a coolant temperature switch in series with the pressure switch. The coolant temperature switch would not close (enable) until the coolant temperature exceeded some temperature (90 C ?) which would prevent the alarm from occurring unless the engine was hot. You could do this with a fixed temperature switch. However, the smarter way to do this would be to use a coolant temperature sensor and coolant pressure sensor and connect them to a Trinket / Teensy / Arduino-like controller. This would allow you to custom tune the temperature and pressure settings to whatever you want. You could monitor actual operating pressure to determine what is 'normal' and pick a setting below that to give you an alarm. The Trinket / Teensy / Arduino is cheap, probably less than $10. Unfortunately the pressure sensor is not so cheap; but, high quality pressure switches are also not cheap.
 
Thanks for the suggestions everyone.

Once the car is warm it should stay warm all day. Senders are nice for logging, but I know my idiot drivers don't look at gauges on the track. Idiot lights I can train the drivers to react to.

I finally got them trained to stop racing and come in when the oil pressure light blinks. I don't think they even know there is a gauge for that on the dash.
 
Coolant level sensor in the overflow tank is the industry standard to monitor for coolant system issues.

If that reservoir gets empty that gives you a good amount of warning unless the car is dumping all its coolant then at least you still know that you don't have any.

I would definitely go with the 960 reservoir. Should be an easy swap
 
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