Rolls-Royce related technical info Supplied by Stephan Knappe

Engine overheat sensor

Rolls Royce Silver Shadow II        SRL40821    US spec

I had the problem that on engine warm-up a buzzer started to work,
but not with full volume. No warning panel lit up though.
Unplugging the engine overheat sensor switched off this buzzing sound.
The overheat sensor is located on the right hand side of the engine (seen
from drivers seat) near the second spark plug from the rear.
The electrical circuit can be checked by grounding the wire connected to the sensor,
if doing so the buzzer should sound loud and the warning light 'ENGINE
OVERHEAT' should illuminate.
This was the case in my car. So I suspected the sensor being faulty.
I bought a new one and installed it. This is very straightforward as the sensor
is screwed just into the cylinder head, no water/oil passages are disturbed.

Being curious, I took the old sensor apart to find out why it was defective.
I found it impossible to open it without destroying.
After opening, it was obvoius why it had failed: It was internally contaminated
with engine oil, presumably caused by a leaking rocker cover gasket.

There's a bi-metal plate in the sensor which 'clicks' up at the pre-set temperature.

I wanted to know at which temperature the switch engages, and found out:
switching on  :  150° C ( 302° F)
switching off  :  140° C ( 284° F)

I measured the temperature of the cylinder head at the sender under normal
operating conditions, it is about 115° C ( 239° F)

I used an handheld electronic temp gauge with surface sensor to check the temperatures.

General note:
The procedures written above are from my personal experience repairing / maintaining my own cars.
I cannot guarantee that these procedures are correct for every car of the Silver Shadow model range,
which have been modified during the production years and for various worldwide markets.