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Why I'm building an exhaust temperature monitor
I was crewing for a good friend of mine. We were sailing down to Penzance from Liverpool, somewhere just around Land's End it's called, I think. The wind was against us and we were in busy waters - fishermen and other boats were around us - and it was pitch dark.
We were doing 1 hour on, 1 hour rest rotation when it was possible. We were motoring for a good hour and a half when the captain came up and switched the engine off.
I didn't hear anything. The exhaust was spitting out as it was expected. From the helm, I could not see anything was wrong. But little we knew...
Luckily, the galley resting spot is right next to the engine compartment and the captain noticed that it was too hot. We pulled out the main and switched off the engine to let it cool down.
The raw water filter came loose in the engine compartment. It fell from its fixed place and bent the pipes, stopping the water circulation. We fixed it on the way - maintaining safe distance from everything - and it was all good after.
But still, this experience was an eye-opener. You have no idea what is going on in the engine compartment when you are up at the helm.
Technical Context:
Most small boat diesels don't have exhaust temperature monitoring. They typically have:
But exhaust temperature rises before coolant temperature, making it an early warning indicator for:
By the time the coolant gauge shows overheating, you may already have damage.
That night got me thinking: why don't we monitor this?
Cars have exhaust temperature sensors. Some motorcycles do. Even modern diesel cars have multiple temperature sensors. But for marine diesels under 100HP? Nothing that I could find.
So I decided to build one.
What I Needed:
From that experience, I knew the requirements:
I'd already built a battery monitoring system using Raspberry Pi Pico and MicroPython, so I knew the platform. For exhaust temperature, I chose:
Sensor: MAX31855 thermocouple amplifier with K-type probe
Processor: Raspberry Pi Pico
Display: Small OLED or LCD
This isn't about replacing proper engine maintenance. It's not about replacing gauges or alarms that came with the engine.
It's about having information.
When you're on watch at night, in the dark, in busy waters... you should know if your engine is starting to run hot. Not when it's too late. Not when there's smoke. Not when the coolant is boiling.
When you can still do something about it.
What's Next:
The code works on the bench. Now comes the real work:
Because the next time I'm on watch in the dark, I want to know.
Source Code: View on GitHub