• Swapped sender for ECU and gauge, after around 5 minutes the gauge goes above hot. Fan is not kicking in at this time, suggesting that the ECU doesn't believe the engine is overheating.

  • I'm still a bit confused about the setup so apologies if this doesn't make sense, but could you have accidentally changed the voltage ratio on the ECU (if it's aftermarket/standalone) so the gauge is reading the incoming voltage indirectly?

    Could be the fan is just on its way out so it seems like there's a wiring/gauge/sender issue but actually the fan is just semi borked?

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