Engine Coolant Temperature Gauge question
audi at humanspeakers.com
Mon Jan 21 14:17:07 PST 2008
> Patient is a 1990 100Q. The wife's car.
> The coolant gauge always seemed to be reading on the low side.
> I drove the car today with the outdoor temperature hovering around
> 15F. Seemed to take a long time for the gauge to start registering.
> I'm wondering if the thermostat is stuck in the open position.
> For the purpose of discussion, I'll provide a textual reference for
> the coolant gauge markings.
> [ ] | [ ] | | [ ] |
> . . . .
> C H
> 1 2 3 4 5 6 7 8 9
> Marking sizes are:
> single wide marker = 4, 6, 7, 9
> double wide marker = 2, 3
> Triple wide marker = 1, 5, 8
> The heater came on after the usual delay . .which takes about a mile
> of travel.
Heat after a mile at 15 dF ain't bad.
> While driving down the highway at 65, the gauge stayed barely above
> the "3" indicator mark.
> When I arrived at my destination, I left the engine running and
> watched the temp gauge. After a few minutes, the gauge crept up to the
> "5" indicator marker, and the radiator cooling fan kicked in.
> Back on the highway, the gauge stayed barely above the "3" marker.
Sounds sort of right - my 89 90Q has two "operating" temps - 1/3 up is
"normal" when it's friggin' cold (t stat open a bit, no need for rad
fan), and 2/3 up is "normal" when it's warm out - that's where the rad
fan stops it from going higher.
> Question 1:
> Should the thermostat keep the coolant temperature relatively
> constant? Even at low temps and highway driving?
It should stop it from dropping below its setting (82 or 87 C, IIRC)
> Question 2:
> What is the usual position of the needle when driving? And what is the
> position of the gauge when the radiator fan kicks in?
Don't know your car, see mine above.
> Question 3:
> I think the dots for positions 1 and 7 are calibration test marks. If
> I remember correctly, the Bentley shows usage of a "Special Tool" to
> test the gauge. More than likely the tool is just a rheostat. Does
> anyone know the resistance values at the two test positions?
> Question 4:
> Does anyone have a simple method of measuring the coolant temperature
> with an external thermometer?
Infrared temp "gun" - any decent shop will have one.
> I was thinking of taping and then insulating my electronic cooking
> temp gauge probe to the Upper radiator hose. With enough insulation
> the outside of the hose should be at the same temperature as the
> coolant inside.
That sounds like fun, at the very least.
> Shhhhhhh . .don't tell the wife!!
Does she, um, have access to teh innertubes?
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