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Reduced mileage caused by coolant temp sensor?; Can a bad sending unit cause reduced mileage?
Topic Started: Feb 1 2010, 11:08 PM (3,426 Views)
dimetrodon


Since last fall, the needle on my temp gauge only goes about half way to the vertical position, and since then my mileage has been lower than normal. I checked the thermostat and it opens and closes just like a brand new 170 degree unit. So I left the original one in. My question is: does the coolant temp sensor influence the engine idle setting and the fuel injection such that an erroneous, low indicated temperature would cause the gas mileage to drop? Or, is my 1990 so technically primitive that there is no connection between the temp sending unit and anything else besides the temp gauge?

Yea, yea, I know: I should buy a factory service manual. You are probably right, and if anyone has one they want to sell, I would be interested.

By the way, does anyone have an engine stand that works nice with the tiny Metro 3 cyl engines? If so, where did you get it and how much did it cost?

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chads4dr


the one in the throttle body is the ECU coolant temp sensor, if its bad then yes mileage will go down, and the car may "act funny" and the car may not enter closed loop. the temp gauge has its own ECT which is located next to the fan switch near the thermostat.
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Bad Bent
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Facetious Educated Donkey

Check: ebay.com/1990+geo+metro+manual for $7 manuals on CD and as low as $11 for a book.

Harbor Freight has a stand for $50 and there's a HF in Loves Park, Illinois (if that's close to you). harborfreight.com/engine+stand
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mwebb
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FOG

probably a thermostat

when at operating temperature , such as it is -
you need to measure the actual temperature of the coolant
an infrared temp probe works well for this but
an accurate
is in accurate
meat thermometer can do in a pinch

if the ground is bad to the coolant temp sensor the value will be elevated and MR ECM will make the mixture richer ....

but
you have 1 known low temp value and
based on symptoms ,
1 suspected low temp value from 2 different coolant temp sensors

that have different grounds

logic says
thermostat is partially open

use only OEM GM OR Suzuki thermostat
why ?
so you do not repeat what you are doing now
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dimetrodon


Bad Bent
Feb 2 2010, 12:26 AM
Check: ebay.com/1990+geo+metro+manual for $7 manuals on CD and as low as $11 for a book.

Harbor Freight has a stand for $50 and there's a HF in Loves Park, Illinois (if that's close to you). harborfreight.com/engine+stand
Jerome,

Thanks for the direction to those eBay manuals. Just bought the paper copies of the FSM and the electrical supplement.
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rmcelwee
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If you pull the thermostat just go ahead and replace it with a new one. No reason to try to save the $5. My guess is that it is the cause of your poor MPGs.
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jellybean


a way to store or do top end work is a plastic milk box(square ones, used to be wood) its a perfect size the flywheel and crank gear are outside the box edges stabilizing the motor
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mwebb
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FOG

red graph ed line is known good coolant temp value
driving the car on local stop and go traffic , about 24f ambient
with grill block .

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