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Coolant pressure warnings and setup

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I have the following sensor fitted to the hot side of the cooling system (after the pump), just before the radiator.

The sensor being used is a 100psi absolute sensor – link below:


The dash’s coolant pressure warning set up is

Less than 100kPa/14.5psi for 1s,

which should be 1 atmosphere. So, if I pull the cap off or more importantly blow a hose or get a leak, the alarm should come on.

I’ve noticed that I’ll get a warning when I’ve just headed out on to the track, maybe lap or so out lap. I wasn’t too concerned until it happens in the first lap of the race and whilst trying not be overtaken and overtaking, I freak out when I see the alarm.

An alarm that you constantly ignore/dismiss is not a very useful alarm.

So the first question is – Have I set the correct warning? How would you set up the warning?

My understanding is I have a sensor that will read zero under vacuum, and anything under 100kPa is a pressure drop from atmosphere and I shouldn’t be seeing this warning when I do.

From looking at the data, it looks like the pressure will get 100kPa or below when the change in temperature across the radiator is over 5*C. In the image below (Sunday’s first session), the differential temp is on the cold side of the radiator, and Coolant temp is taken from the back of the head near the radiator. DeltaT = Cool temp – Diff Temp.

Coolant pressure is shown in the top group and I have added a channel to show the cap release pressure (22 psi). You can see the pressure trending down to ~100kPa [point 1] showing roughly where the alarm went off.

The second image shows pretty much the same thing [point 4]. These both happened on the first flying lap. I have had it the warning 2 or 3 laps into a race as well.

[Points 2] and [point 3] in the first image are shown in more detail below. Not sure what’s happening here, but it appear to be rev related – once the revs go past about 7k, the pressure fluctuates rapidly.

Question 2 – Is something wrong? The sensor seems to work as expected.

Any thoughts/help would be greatly apricated!

I think the problem is the coolant temps are just too low to cause a pressure change. Your alarm probably needs to include a check for temperature (say 85degC and above when you had pressure) -- it will mean you can't detect a coolant leak at low temps -- because you can't detect a coolant leak at cold temps. the pressure is too close to ambient.

One solution -- high-end motorsports engines pre-pressurize their coolant systems to avoid cavitation (probably those pulses you see at 7000 RPM). If you added a schrader valve to your header tank, and use a bicycle pump to add about 3 PSI (so take your sensor to about 120 kpA when cold). Then your test would probably work as is.

Excellent suggestion!

Thanks David!

I suspected that too, and did have a temperature consideration in the warning, but only if above >60*C. I'll try increasing it at the next test day, and also suss out a way to add pressure to the system - that's a pretty neat idea.


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