Coolant pressure sensor

[Driver+Passengers]

I've been having a few discussions with some members on here... I have a suspected head/gasket failure, though it's not confirmed. Before I do anything else to the coolant system, I want to install a pressure gauge.

I've just ordered 3 of these:
http://uk.farnell.com/jsp/search/produc ... ku=2080494

I'll post the build process here, and hopefully some graphs of my datalogging efforts.

Basic idea is that I'm going to epoxy the sensor into a barb connector, possibly fill the void with a dod of heavy grease, (though the part I've gone for does have a media resistant gel miniscus already), and pop it into the bleed hose. Then hook it up to an Arduino to read the voltage.

[Rhinoman]

That type of sensor is not designed for use with fluids, I would try and find one that is although when I've used them in the past they have been quite expensive.

[Driver+Passengers]

That type of sensor is not designed for use with fluids, I would try and find one that is although when I've used them in the past they have been quite expensive.

Cheers for raising that. True, but I have done my research and hopefully I'm still on the right track with this. I'd still be keen to hear what you think after reading this.

The media resistant gel (Sifel) used in this product variant is a start. The manufacturers have additionally recommended a heavy molecular weight silicone grease barrier. I have yet to select the grease that I will use but they recommend Parker O-lube, DMS-T46 or T51. In terms of contaminants, the grease must be free of halogenures (Cl content < 50 ppm). I don't know what that means yet.

They have also referred me to an application note http://www.freescale.com/files/sensors/ ... AN3728.pdf and the "Quality and Reliability" and "Sensor Media Compatibility" sections of their Device Data Handbook http://cache.freescale.com/files/sensor ... /DL200.pdf (25MB).

I am aware that this sensor measures pressure relative to a sealed vacuum, whereas I really want a differential pressure sensor with one port open to atmosphere. I could always use two and compensate in software.

I'm initially just wanting to log the pressure profile during operation as the system is now and to use that data as a basis for comparison with the behaviour observed after I have carried out repairs. That said, I probably will end up leaving it in. If it corrodes and fails, I'm ok with that. If it fails to such an extent that I drop coolant, I'd be less happy, but that should trigger my alarm anyway.

[Northern Bongolow]

the edge of the envelope is the best place to be . what out for the flat spin though top gun

[Driver+Passengers]

the edge of the envelope is the best place to be . what out for the flat spin though top gun

I don't know what you mean...!

Sensors arrived today. I'm currently hunting grease and a hypodermic needle...

[Northern Bongolow]

chemist sells needles, go in with your sleeves rolled up though. .
if your struggling i have some that i use for ink cartridge re filling, they have a wide hollow needle.think asda sell them.

[Driver+Passengers]

if your struggling ...

Found a needle - works with Nerita HV, but I'm still to source the right grease.

I've clipped off the N/C pins from the chip, shaved off the pimples on the bottom of the package and epoxied onto it a 0.1" pitch, three pin connector. No locking tab, so I'll use a zip-tie on the final assembly as strain relief. When it's dry, I'll solder on short link wires, test it and then encase the bottom in hot glue.

[Northern Bongolow]

yes thats what i would have done.









if i could have seen it.

[Driver+Passengers]

First bench test: 5V supply to pin 2, ground pin 3. Open to atmosphere, I get a reading of 1.17V from pin 4.

The sensor responds by 12.1mV/kPa. With a bendy straw placed (leakily) over the dry port (no grease)...

Sucking: 1.06V, -9kPa or -1.3psi
Blowing: 1.30V, +11kPa or +1.6psi



Header tank pressure cap should vent at +1.1bar, or +16psi and suck in at -1psi. Ady reckons on a typical running pressure for his vehicle of 10psi. So I'm looking at a range from -6.9kPa to +110kPa, or offsets from -0.08V to +1.33V. Depending on atmospheric pressure then, I'm looking at reading the sensor output voltage in the range roughly 1.1V to 2.5V, with a steady running pressure of 10psi giving a reading of somewhere in the region of 2.0V.

Scientific stuff!

Edit: this is all based on the assumption that the pressure observed at the end of the bleed tube is going to be the same as at header tank cap. This assumption is probably wildly incorrect. TBD

[Driver+Passengers]

Blowing: 1.30V, +11kPa or +1.6psi

http://answers.yahoo.com/question/index ... 317AALDybN

[Northern Bongolow]

Edit: this is all based on the assumption that the pressure observed at the end of the bleed tube is going to be the same as at header tank cap. This assumption is probably wildly incorrect. TBD

its going to be very similar matt. give or take the pump pressure, if the motor is running/revving.

[Driver+Passengers]

Edit: this is all based on the assumption that the pressure observed at the end of the bleed tube is going to be the same as at header tank cap. This assumption is probably wildly incorrect. TBD

its going to be very similar matt. give or take the pump pressure, if the motor is running/revving.

Even taking into account the small bore of the bleed hose? I have to admit, I haven't quite got my head around fluid dynamics, yet.

[g8dhe]

Size of tube has no impact on the pressure if there is no flow in the tube.

[Driver+Passengers]

Quick notes on grease selection.

From the little I've read, lithium-based greases have a relatively low dropping point and are relatively poor at resisting water. Silicon grease has much better resistance to water and will generally stay viscous to higher temperatures.

Therefore, despite the local factors, Halfrauds and a couple of DIY stores being unable to supply me with a silicone grease, I am not going to make do with what's in the garage just yet. Apparently, silicone grease can be sourced from plumbing supply stores, though whether of suitable weight and temperature range, I don't know. I want to get this right...


Also, notes on epoxy.

I hadn't realised that epoxy does not do well with heat. The cheap stuff from the pound shop practically melted when I was soldering the wires onto the connector - granted it wasn't fully hardened. Looking at the branded packets in the shop earlier suggested a 70-odd degC upper limit. So I went for some Evo-stik Super Fix putty to seal the sensor into it's 'housing' - good to 120 degC, waterproof, resistant to vibration, etc.

[Driver+Passengers]

Size of tube has no impact on the pressure if there is no flow in the tube.