Facelift, CF2 models: rocker switches in panel to one side of inset dash panel.
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Temperature sender

Post by gallaghermartinpaul » Wed Aug 05, 2015 5:48 pm
Hi all,
Does anyone know the values in ohms that an AC delco temp sender, small model screwed into threaded insert which itself screws into manifold, 1/2 AF, serial no: 7966*****? should give when hot & cold? On a 2000 setting it's giving c850-900 cold and c200 cold. Sound right? It gives no reading on the dial. Gauge goes off scale when earthed to outer sensor body. Sourced a very similar looking Vauxhall unit intended for a Chevette, this gives much lower readings: c150 cold, 100 hot but, somewhat counter intuitively, only gives minimal movement on gauge, not even out the blue. I'd assumed that lower ohms=less resistance=better earth & higher reading on the scale; clearly not the case. All advice gratefully received, we've got a trip from Oxford to Scotland looming and, with a one ton trailer permanently attached to the rear of the van, a functioning gauge would be reassuring.

Re: Temperature sender

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Post by Phil Bradshaw » Club admin » Wed Aug 05, 2015 9:38 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4755
Nominal resistance at 20C should be 0.5 MΩ or greater.

Resistance at 90C (approximate cut-in temperature of viscous coupling fan, gauge reading about 2/3 scale) will be around 100Ω, at 100C about 80Ω (gauge approaching or just going into red).

Sender unit is a 'negative temperature coefficient' semi-conductor device.

Gauge is a hot wire instrument and the sender wire ought not to be earthed because the heating wire may burn out.

Use a 40Ω 10W (wire-wound) resistor between the sender lead and a good earth, when gauge should read maximum when ignition switched on.

An alternative to a resistor is a 4W test lamp: lamp should glow dimly and gauge should read around maximum (actual pointer deflection depends on bulb resistance which can vary).
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

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