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300Tdi Overheated - but what is this sensor


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1995 300Tdi Mk1 Disco

Just got back from Kamdiffs with my Defender doors. I managed to get from Godalming to Jn 7 on the M3 by myself, but then needed a lift back on the back of a recovery lorry to Trowbridge!

Whilst the temperature gauge was reading normal, the engine lost power, then smoked like an autumn bonfire! Quickly pulled over and opened the bonnet (after releasing the strap that was holding it down - another saga!) The assumption is that it has overheated - why the gauge didn't move, I don't know - a new one will be on order!

What I have noticed is that a sensor on the top middle of the engine over an exhaust manifold is well melted, including the wiring. Looks like a brown/black and a green or blue.

The question is - what is this sensor and is it preventing my engine from starting? (The engine turns over, tries to start but won't run).



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Hi Peter, sorry to hear about your misfortune. There is a saying doing the rounds that Land Rover temperature gauges tend to lie............It is common practive to replace the temerature gauge and sending unit on the Defenders with a VDO gauge, it fits in the same opening the standard gauge fits.

The Tdi's with factory fitted aircons has three sending units around the thermostat housing: One for the temperature gauge, one will bring in the electric condenser fans, irrespective if the aircon is on or not, and the third one I am not shure about.

Here in South Africa we fit one of two aftermarket engine monitoring systems, the Little Black Box or the Madman Engine Monitering System. They work much bettewr than the std LR temperature gauge, and includes a coolant level monitoring/warning system

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The sensor was melted on mine as well. Turned out the head was warped beyond recovery and was cracked as well. Bought a nice new shiny one from Turners in the end.

RRB is correct in that if the sensor tip is out of the water it won't register a heat increase - hot air doesn't make it work.


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