XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

Facelift AJ16 Reporting Low Fuel Economy

 
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Old 03-15-2019, 06:54 AM
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Default Facelift AJ16 Reporting Low Fuel Economy

I have a 1996 Jaguar XJS, AJ16 engine. About 113k mikes.

I do a mix of city and highway driving. I seem to be averaging 15mpg. While I donít drive conservatively, Iím also not hammering down the gas pedal at each green light either.

My LTFT is zero. Both banks.

The only unusual reading Iíve picked up is that my coolant never goes about 180. With the heat on its at 176F and without heat, itís at 179.6F.

Would a stuck open thermostat cause that kind of fuel economy?
 
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Old 03-15-2019, 07:20 AM
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An open thermostat will definitely increase fuel consumption. I'd replace it and see what the outcome is, rather than worry about looking for any other problems at this stage.
 
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Old 03-15-2019, 02:42 PM
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Excellent. I have a thermostat set at 88C on it’s way! That’s going to be about a 10 degree difference, and more importantly warm up the engine faster I imagine.
 
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Old 03-24-2019, 02:21 PM
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Replaced the thermostat with the OEM Waxstat thermostat. The sender is now pointing the needle dead center of the N, but the OBD2 reader is still showing 176-179F.

I wonder if the them temp sensor is bad.
 
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Old 03-30-2019, 03:09 PM
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It was the temp sensor. The car is now showing 192F when driving...I may have replaced a perfectly good thermostat!

I will come back and share mileage after about a week.
 
 
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