DIY Multi-Point Engine Temperature Monitoring

[Robfz]

For the past few years I’ve been running a simple DIY system to keep a closer eye on my engine temperatures. It’s been solid and I know other boaters using it as well. The main idea is early warning — loud alarms or flashing lights when something goes wrong, instead of waiting for the dash gauge to react.

What it does:

• Siren or flashing light when temps exceed safe limits
• Multiple sensors at once (raw-water elbow, coolant, thermostat, alternator)
• Trend history to see what’s “normal” and spot changes early

How it’s set up:
I’m using an inexpensive ESP32 microcontroller with waterproof DS18B20 probes (a couple of dollars each). They strap onto engine parts and all share a single wire bus, so you can expand easily.

On my boat:

• Raw-water elbow: normally 38–40 °C, alert at 42 °C (impeller / intake issues)
• Alternator body: useful with lithium batteries that put heavy load on it
• Coolant area
• Near the thermostat

Alarms & display:
If the alternator climbs above 100 °C, a siren sounds immediately. I also get dashboard readouts so I can compare elbow, coolant, and alternator temps during normal operation.

This setup has already given me early warning of restricted raw-water flow before the stock gauge showed anything.
Has anyone else added extra engine temperature monitoring beyond the factory gauges?

 

[captmikem]

I find it handy to put a sensor on the shaft stuffing box as well.

 

[Waterant]

This is another option for simple monitoring of exhaust temperature, indicating a lack of raw cooling water: Products – Borel Manufacturing

We installed it on both engines. Installation is straightforward, requiring only a couple of wires.
It will alert to a problem well before the engine temperature rises to a dangerous level.

 

[Comodave]

This is another option for simple monitoring of exhaust temperature, indicating a lack of raw cooling water: Products – Borel Manufacturing

We installed it on both engines. Installation is straightforward, requiring only a couple of wires.
It will alert to a problem well before the engine temperature rises to a dangerous level.

I have put this on several boats, love it.

 

[lwarden]

I like this setup. Are you reading these back to a Raspberry Pi board? Can you give some detail on how many sensors you are able to add per ESP32 WiFi module?