Coolant pressure sensor

[Driver+Passengers]

For what it's worth, today's readings...


The rise to 9psi at around 680 was nailbiting. Temp gauge started creeping towards what I know to be 90ish, but creeping rather fast. I said to the boy "I think we have a problem, oh no!" to which the 4yo replied "have you got all the tools, daddy?". (I'm not sure, is it even legal to get him to step on the accelerator until the needle's pointing at the 3 and hold it there for a minute or so??? We didn't have to find out.) Anyway, it dropped again of its own accord. I'd been parked at Tesco for about 20 minutes and I think something worked its way out in the first mile or two after that.

[The Great Pretender]

Well, I made it. 270 miles and no major dramas. I'm making a right pigs ear of this, though... overpressuring every time I put the foot down, leaking out of the header tank, one near overheat this afternoon which seemed to sort itself and otherwise a light foot and a keen eye - all in all a tense drive.

Almost certain it's the head.

You could fit an auxiliary expansion tank and extend the blow off pipe to the base of it, then any coolant passed will not be lost just sucked back in.
Most peoples problems are in their heads.

[Driver+Passengers]

I've isolated a point in time on during the first of the two long runs where I was up to 60, slowing to 45/50 odd and pushing back up to 60 again.



The total time for this trace is 2m15s with a sample interval of 5 seconds. You can clearly see the three occasions on which I put my foot down (staying in 4th with lockup), @7, 12 and 16. Then @20, I stopped at a roundabout then pulled away relatively gently.

Two problems with this: I wasn't logging TPS and there was a air/pressure leak from the header tank. The first is covered my the description of what I was doing at the time and it looks like it can be directly inferred from the pressure chart. The second suggests that this trace should probably look worse if I hadn't a leak.

The reason I'm replacing my head gasket right now is more or less as a direct result of this (apparent) behaviour.

[The Great Pretender]

I look forward to seeing the results, hope it solves your problem.

[Driver+Passengers]

Fitting the sensor to the header tank has resulted in a pressure leak (or perhaps more than one). Combination of epoxy putty and 2-part epoxy still hasn't cured it, so I'm going to refit a sensor to the bleed hose, compare values with the one in my header tank and then replace the header tank with one that hasn't been tampered with.

For the time being, I'm sticking with the MPXHZ6400AC6T1 - just ordered 5 units from Farnell for £27.00 inc VAT. They're -1 bar to 3 bar, which is more than I need but they're cheaper than the lower range options.

After replacing the head gasket (see viewtopic.php?f=3&t=58441) there are no signs of coolant pressure rising under load, so I think I've "fixed" it. However, I need a few more traces to be sure.

Here are two traces since the gasket was replaced that show the pressure leak(s)... cold, static pressure tests on the left, road tests on the right. I've smoothed the second trace using 15 second moving averages (sample period 5s).

[Driver+Passengers]

Still leaking, but still driving. Peaked higher this time. Sharp drop at 200-odd represents about 45 minutes stopped.



More sensors should arrive tomorrow, so I can get the bleed tube monitored again and replace the header tank.

[Northern Bongolow]

your 10 pounds peak looks about right matt.

[The Great Pretender]

Glad it looks like it was the head gasket.
It will be interesting what you get with your tank sealed and reliable graph results.

[Driver+Passengers]

Cheers, Ady/Mel.

Time will tell...

[DILLIGAF]

Re silicone grease, www. beaversports.co.uk AQUAGEL silicone grease diving lube and protector.
Don't know if that is any help, if you know anyone who dives they might have some to save you buying a whole tub, but its not that expensive.

[Driver+Passengers]

Re silicone grease, www. beaversports.co.uk AQUAGEL silicone grease diving lube and protector.
Don't know if that is any help, if you know anyone who dives they might have some to save you buying a whole tub, but its not that expensive.

Thanks, I got a tube of Carlube silicon grease.

Disappointed that Farnell's next day delivery is not next day for <1kg items - I am at the mercy of Royal Mail.

[Driver+Passengers]

Sensors in today.

One problem with a sensor at the end of the bleed hose is that the position in which the bleed hose is secured will affect the reading it gives because in addition to the 1atm air pressure in an otherwise unpressurised system, the head of water above it will also register a positive pressure. This will vary depending on the incline of the vehicle and the water level to begin with.

With an accelerometer, three pressure sensors (header tank, bleed hose and atmosphere), a fixed, known mounting point for the end of the bleed tube and a bit of maths and some careful calibration, this could be made to work as a coolant level sensor. I will not be trying this any time soon, and I doubt it would give 1cm accuracy which is what I'd want.

[Driver+Passengers]

I have braved it and put a pressure sensor in Peter's header tank, drilled sanded and then carefully epoxied into the small blanked stub at the top left. Curing in the house just now. Bleed tube assembly done last night. If this header tank sensor causes a problem, it should be easy to remove and blank again - no harm done.

Will need to modify the Arduino to take two pressure sensors, swap tanks over later today for a cold pressure test, then if it looks like its holding pressure, bleed up, let it cool down somewhat and then take it for a test drive.

I hope to answer the question "does the coolant pressure apparent at the end of the bleed hose differ from the air pressure at the top of the header tank under driving conditions?". I don't have the protection circuitry in place yet to be able to sample the TPS, nor do I have any temperature readings being logged, but I really just want to see the traces next to each other to begin with.

[Driver+Passengers]

Peter's header tank installed with integrated pressure sensor. Cold bleed and cold pressure test ok. Using a small mirror and a work light, I tightened one hose clamp and re-seated a spring clamp to stop a couple of small drips and it's held well for 15 minutes. The average (red) line crosses from above to below the 12psi line at about 100, which corresponds with when I released and retightened the spring clamp - a few more drips came out there. A longer run should show up and further pressure leak over time.

Photos to follow.

[mikeonb4c]

Peter's header tank installed with integrated pressure sensor. Cold bleed and cold pressure test ok. Using a small mirror and a work light, I tightened one hose clamp and re-seated a spring clamp to stop a couple of small drips and it's held well for 15 minutes. The average (red) line crosses from above to below the 12psi line at about 100, which corresponds with when I released and retightened the spring clamp - a few more drips came out there. A longer run should show up and further pressure leak over time.

Photos to follow.

Just remind me quickly what all this is about Matt. Without trawling back through the pages of posts, what is causing the interest in measuring pressure in the system (I dimly recall that once it might have been to do with leaking head gasket, so are we now trying to see if a changed set of results suggests the problem has been cured?).