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Old 11-06-2021, 12:32 PM   #1
rb92673
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Default Water pressure switch

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?

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Old 11-06-2021, 12:52 PM   #2
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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.
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Old 11-06-2021, 01:26 PM   #3
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Originally Posted by dl242gt View Post
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.
Thanks. I like that idea.
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Old 11-07-2021, 02:02 AM   #4
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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.
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Old 11-07-2021, 11:43 PM   #5
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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!
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Old 11-08-2021, 11:09 AM   #6
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Originally Posted by Toybox View Post
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.
I like the idea of idiot light overkill. I'd probably wire both to the same light.

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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!
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?
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Old 11-08-2021, 09:05 PM   #7
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You could use a fuel pressure gauge [0-15lbs] tied into any where in the system.
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Old 11-09-2021, 03:02 AM   #8
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Quote:
Originally Posted by rb92673 View Post
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?

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.
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Old 11-09-2021, 10:05 AM   #9
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Quote:
Originally Posted by 283SD View Post
You could use a fuel pressure gauge [0-15lbs] tied into any where in the system.
Auto meter makes a coolant pressure gauge.
https://www.summitracing.com/parts/atm-4307

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Originally Posted by rb92673 View Post
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.
Drew's lemons car has big idiot lights and an idiot buzzer. No oil pressure? it screams at you..
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Old 11-09-2021, 10:08 AM   #10
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I knew a guy who mounted a brake light on the dash for a low oil pressure light after his daughter locked up a motor with no oil in it.
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Old 11-09-2021, 11:58 AM   #11
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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/produc...ressure-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.
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Old 11-09-2021, 12:48 PM   #12
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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.
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Old 11-09-2021, 02:53 PM   #13
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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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