Engine Protection • Sensor Switching • Retrofit
Flexible Sensor Switching with Bolec BEM502IRN + EA101 + FL301
Build a modular engine monitoring system that lets you set precise switching points (e.g. coolant temp 96 °C),
add extra sensor inputs, and reduce long-term maintenance risk—without being locked into hard-to-source legacy sensors.
Quick takeaway
With a BEM502IRN as the core shutdown monitor, plus FL301 for precision setpoints and
EA101 for added inputs, you can build custom switching logic that many fixed-function watchdog systems can’t match.
Why modular switching matters
Many engine protection units are “fixed function”: you get a limited number of inputs and you’re often forced to use specific
switch-type sensors. That’s fine until you need a custom setpoint, a non-standard alarm action, or you discover the original sender
is becoming expensive or hard to source.
A modular approach lets you keep the core shutdown protection robust, while adding adjustable and expandable switching
on top—so the system adapts to your engine, not the other way around.
The core monitor: BEM502IRN
The BEM502IRN is a compact electronic monitoring system with multiple dedicated fault inputs and a shutdown output relay,
typically used to control a fuel solenoid or engine run circuit. It also includes start-up bypass timing and fault memory/recall,
making it well-suited to irrigation, industrial, marine, and stationary engine applications.
Precision switching example: coolant temp OFF at 96 °C (FL301)
Suppose you have a water-cooled engine and you want the system to switch OFF at exactly
96 °C—not at an arbitrary fixed switch temperature, and not by hunting for a rare, legacy temperature switch.
The FL301 is designed to trigger an alarm output when a gauge reading passes a predetermined level.
Because it works with variable resistance senders (via the gauge signal), you can set a precise threshold using the built-in
adjustment pot, then use the relay output to feed a shutdown input on the BEM502IRN.
How it’s typically wired (concept)
- Temperature sender → existing gauge (no change to the gauge wiring)
- FL301 “piggybacks” the gauge sender terminal
- FL301 relay output → BEM502IRN input (configured as a temperature/high-temp shutdown path)
- When gauge reaches 96 °C equivalent point → FL301 switches → BEM502IRN shuts engine down
Add three extra inputs (EA101)
Need more than the standard set of protection points? The EA101 provides
three adjustable alarm channels for standard resistance gauges (e.g., VDO-type systems),
switching to ground on fault. This is ideal for adding extra protections like:
- Low gearbox oil pressure
- Auxiliary oil pressure / hydraulic pressure
- Additional temperature points (aftercooler, gearbox temp, etc.)
You can route each EA101 alarm output into available shutdown/alarm inputs on the BEM502IRN or into external alarm logic,
depending on how you want the system to behave.
Cost & long-term value
A typical retrofit / modification using these modules is often around
AUD $250–$300 in parts and setup (application dependent).
The bigger win is long-term: by switching based on common gauge/sender signals and adjustable thresholds,
you reduce dependence on obscure, engine-specific switch sensors that may become difficult to source in the future.
That means fewer urgent breakdown purchases, less downtime, and lower total cost of ownership over the life of the engine.
Want help planning your retrofit?
Tell us your engine type (water-cooled/air-cooled), existing gauges/senders, and the setpoints you want.
We can recommend a clean, serviceable wiring approach.