re: Oil Pressure Going Lower

[Godfrey DiGiorgi <ramarren@domain.elided>]

>Following up on Graham's and Eric's recent posts on this subject,
>I to recently had the oil pressure sending unit on my '91 Spider
>go kaput. Ordered the replacement unit from IAP and installed
>same but guage only reads to about 10 psi at speed and 0 at idle.
>Cleaned the connection and coated with battery grease but still
>no change. I'm not terribly concerned but likewise curious as to
>what gives with these things.

Gauge sending units and readout heads often seem a bit twitchy,
particularly used ones. The one in FrankenSpider was reading just about 0
at idle and only up to around 50 at speed, so I had the shop check the
pressure with a mechanical gauge and swap in the sending unit from the '78
hulk. Now it reads over 60 psi at speed and never drops below 30 or so. 

Having once worked at an instrument rebuilder, the right thing to do is to
have both the sending unit and the gauge calibrated together on the bench
for accurate readings. It doesn't seem to matter whose gauges they are,
they are all like this far as my experience shows. 

(I have it on good authority that this problem, coupled with the lack of
knowledge of most of their customers, has pushed Jaguar to a really
extreme solution: they use the same pressure sensor on the low pressure
warning light as they do on the gauge in late model sedans, and fit a
resistor in the circuit so the gauge will ALWAYS read the correct
pressure. That raised the customer satisfaction index: the gauge is now
exactly as useful as an idiot light but the customers don't complain when
it drops to 6psi at idle when hot...Sure looks nice to have an oil
pressure gauge on the dash, though. !)

Godfrey

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