Ok, before you all say that I need a new thermostat, I've been there.
The engine temperature guage seems to regulate to the first, thin white
line at about 1/4 on the guage. There is a thick white line
just below half way up the guage where I would expect the needle to settle.
The needle only gets there on warm days in the summer
or if I let the car idle stopped for some long period of time. Somewhat
farther up the guage(just above half guage) the fans turn on,
as I would expect also. The heater blows very slightly warm air if the
outside temp is below, say, 45 degrees.... unless I let the car
sit idling long enough to get the gauge up to or past the thick white line I
mentioned before. Then the heat seems to work fine. If the outside
temp is below 40 or so, the "Heat" makes my feed cold!
If I'm moving, even at slow speeds, the gauge settles back the the thin
white line at about 1/4 again.
Also, the oil temp only just comes off the cold mark (60degrees C) to
the first white mark at about 1/6 the guage. The engine has
an oil cooler so I wouldn't expect the oil to get much above the coolant
All indications are that the engine is not getting to full operating
temperature. I've replaced the thermostat twice, once because it really
failed. I've installed the 97 degree C thermostat, not the 87. And still,
very low heater output, and the needle stays at about 1/4 on the gauge.
There is no indication on the gauge as to what the temperature value is.