Oil temp gauge misbehaving

[remdiw]

I have 3 VDO gauges in my 67 Dormobile, oil temp, oil pressure and cylinder head temp. The oil pressure and cylinder head temp gauges work great. The oil temp gauge - not so much. As the engine warms up the oil temp gauge works fine until it hits about 200 degrees. Then the needle jerks and quivers and ultimately pegs. I had the gauge bench tested - it was fine. Then I replaced the sending unit (oil relief plug location). All the sending units are VDO to match the gauges. I’ve checked connections including ground. Is it possible that at 200 degrees something happens in the oil relief gallery that could explain the erratic temp gauge? Any other thoughts? I’m stumped!

[flemcadiddlehopper]

I would see what the sender is doing by attaching a ohm-meter to the sender wire and ground when it is at the temp that the problem occurs. A analog ohm-meter would work best for this as you'll be able to watch the needle bounce. The sender is just a variable resistance to ground for the gauge.
My thoughts would be that the problem is in the gauge, not the sender. Although you should verify you have steady power to the gauge and double check that there is no ac power (alt) in the system. Also check the integrity of the sender wire with an ohm-meter to the wire and ground, with the wire disconnected from the gauge and the sender.

Gordo.
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