At 08:08 PM 4/25/2010, Jake de Villiers wrote:
>Under load the engine's making a lot more heat than that - the oil
>gets up towards 235 degrees too...

Incidentally, if I'm reading the temp gauge nomenclature correctly,
the needle begins to enter the overheat zone and the blinking light
comes on at 115C/240F.  That's about 20F below the coolant boiling
point at 12 psi system pressure.  I'd expect the oil temp to be
greater than the coolant temp under most operating conditions.

The actual operating temperature doesn't have a huge amount to do
with this stuff -- the issue is whether the cooling system can carry
away more heat than the engine is putting into its internal
coolant.  If not, the thermostat (of whatever temperature, even say
100F) will be fully open and the system temp will begin to rise,
triggering the fan.

However in our vans (2.1l, numbers slightly different for 1.9l) in
order of rising temperature:
81C/178F (at radiator) slow speed fan shuts off.
~85C/185F (at engine) thermostat begins to open.
87C/189F fast fan shuts off.
89-94C/192-201F slow fan starts.
95-100C/202-212F fast fan starts.
~105C/221F thermostat is fully open.

The radiator switch *appears* to be one or two tubing passes after
the input.  For what it's worth, here are the numbers I've just
gotten, idling in still-ish air at about 55F.

Facing the vehicle:  Fins near bottom left run about 93-94C until the
fan comes on.  Fins near bottom right climb to 89+C and the fan comes
on.  It goes out somewhere around 78C.  Fins near top left rise to
close to what the bottom-right is until the fan comes on, then are at
about 55C when the fan goes off.  All fin temps of course drop
somewhat instantly when the fan starts.

Yours,
David