Over the Winter, I fitted a 'Cockpit' oil temperature gauge.

You receive a replacement sump plug and the sender unit screws into the 
centre of the plug. The first plug/sender unit combination had to be 
returned because the hole in the plug was misaligned. The second unit, now 
fitted, is not much better and there's an oil leak from the threads.

The gauge, standard size, just fits (only just) in the metal between the 
ashtray and the radio/cassette.

Running temperatures, so far (May, UK) are typically 40 - 80 degrees 
centigrade.

David Tonks
1973 Westfalia (UK)