orca4wd Posted March 4, 2010 Share Posted March 4, 2010 (edited) Recently my 1995 3.0L A/T Pathfinder with only 85K miles temperature gauge reads low (approx 1/8 above "C" mark). Heater is blowing warm/hot air while travel within 5 mins of driving. Gas mileage seem to went down to 14-15 MPG instead of 17-18. Idle seem to be high (1500 RPM) while cold then drop to the normal 800 RPM when settled within 5-10 mins. I tried to search for this issue and came to several conclusions: 1) Thermostat may be stuck open 2) Bad ECU temperatre sensor 3) Bad thermal transmitter (a.k.a engine coolant temperature sensor). My understanding this sensor goes to the temp gauge. With the above symptoms..can someone please chime in with their expert advises? Appreciate your help and look forward to your reply. Richard. Edited March 4, 2010 by orca4wd Link to comment Share on other sites More sharing options...
ac92pathfinder Posted March 4, 2010 Share Posted March 4, 2010 Recently my 1995 3.0L A/T Pathfinder with only 85K miles temperature gauge reads low (approx 1/8 above "C" mark). Heater is blowing warm/hot air while travel within 5 mins of driving. Gas mileage seem to went down to 14-15 MPG instead of 17-18. Idle seem to be high (1500 RPM) while cold then drop to the normal 800 RPM when settled within 5-10 mins. I tried to search for this issue and came to several conclusions: 1) Thermostat may be stuck open 2) Bad ECU temperatre sensor 3) Bad thermal transmitter (a.k.a engine coolant temperature sensor). My understanding this sensor goes to the temp gauge. With the above symptoms..can someone please chime in with their expert advises? Appreciate your help and look forward to your reply. Richard. i would replace both of those. Link to comment Share on other sites More sharing options...
silverton Posted March 4, 2010 Share Posted March 4, 2010 I have noticed my truck does the same thing. the fuel gauge still works fine though. there is some sort of resistor pack on the backside of the cluster from what I've read, but since the fuel gauge still works fine I don't think it would be that. The needle climbs a little higher than usual, MAYBE 1/4 of the way up when I'm pulling hard up a hill, but usually just hangs out just above the beginning of the "normal" mark. Also, the air coming through the vents isn't exactly HOT, but it's not really cold either. It's almost like it's just lacking a thermostat. Which could be the case really, most newer thermostats have a "failsafe" where they will freeze open, instead of closed like back in the day. One of the things I'll change out on my upcoming timing belt change. Link to comment Share on other sites More sharing options...
94pathfinder Posted March 4, 2010 Share Posted March 4, 2010 Recently my 1995 3.0L A/T Pathfinder with only 85K miles temperature gauge reads low (approx 1/8 above "C" mark). Heater is blowing warm/hot air while travel within 5 mins of driving. Gas mileage seem to went down to 14-15 MPG instead of 17-18. Idle seem to be high (1500 RPM) while cold then drop to the normal 800 RPM when settled within 5-10 mins. I tried to search for this issue and came to several conclusions: 1) Thermostat may be stuck open 2) Bad ECU temperatre sensor 3) Bad thermal transmitter (a.k.a engine coolant temperature sensor). My understanding this sensor goes to the temp gauge. With the above symptoms..can someone please chime in with their expert advises? Appreciate your help and look forward to your reply. Richard. i'd be more than happy with 14 mpg Link to comment Share on other sites More sharing options...
adamzan Posted March 4, 2010 Share Posted March 4, 2010 Thermostat. Mine did the same thing. Couldn't hurt to change it anyways. You are getting close the timing belt/waterpump time as well. Link to comment Share on other sites More sharing options...
Kingman Posted March 4, 2010 Share Posted March 4, 2010 If your thermostat is sticking open and causing the engine to run cold, you mileage will likely drop a little. The hotter the engine runs the more efficient it is. I'm having the same problem, gauge reading a little low and mileage is in the pits. Link to comment Share on other sites More sharing options...
darkestskydiver Posted March 4, 2010 Share Posted March 4, 2010 glad i saw this thread, i have a similar issue as well alltho my guage never moves off of cold. unless it's summer time and i idle alot. Link to comment Share on other sites More sharing options...
silverton Posted March 4, 2010 Share Posted March 4, 2010 If your thermostat is sticking open and causing the engine to run cold, you mileage will likely drop a little. The hotter the engine runs the more efficient it is. I'm having the same problem, gauge reading a little low and mileage is in the pits. I wouldn't say it runs more efficient, but when it never hits "operating" temp, the engine stays in closed loop and always thinks it's cold so dumps in extra fuel to compensate. Link to comment Share on other sites More sharing options...
orca4wd Posted March 5, 2010 Author Share Posted March 5, 2010 i would replace both of those. I do not mind the gauge reads low given engine is performing at normal status. Hope the cold engine won't harm engine durability. My guess is the thermostat is probably stucked open because of the lower gas mileage and low reading on gauge. If is the gauge temperature sensor is bad then it should not affect the MPG...Right? If the ECU temperatre sensor is bad then it should not affect temp gauge..Right? I am trying to reason this out so that I don't have to spend un-necessary expenses. BTW - Anyone know the approx price for these parts and where is the best place to purchase them. Thanks to all who reply! Cheer... Richard. Link to comment Share on other sites More sharing options...
Chriskaw440 Posted March 6, 2010 Share Posted March 6, 2010 I do not mind the gauge reads low given engine is performing at normal status. Hope the cold engine won't harm engine durability. My guess is the thermostat is probably stucked open because of the lower gas mileage and low reading on gauge. If is the gauge temperature sensor is bad then it should not affect the MPG...Right? If the ECU temperatre sensor is bad then it should not affect temp gauge..Right? I am trying to reason this out so that I don't have to spend un-necessary expenses. BTW - Anyone know the approx price for these parts and where is the best place to purchase them. Thanks to all who reply! Cheer... Richard. My 1990 SE has the same issue...sometimes its normal temp reading, sometimes way low...and it seems like my mileage is worse when the temp gauge is reading low. Mechanic friend that worked on my vehicle a while back says my temp sensor connector/wiring is the culprit (the sensor that is on the coolant neck above the fan area) and sometimes I wiggle it around, make sure its firmly connected and the temp does read more normal for a while. The connector is so oil and dry rotted (plastic) that it just doesnt seem to want to stay tightly in contact. I ordered a new sensor and will probably just hardwire it direct since I doubt I can find a new connector anywhere. Link to comment Share on other sites More sharing options...
orca4wd Posted March 6, 2010 Author Share Posted March 6, 2010 My 1990 SE has the same issue...sometimes its normal temp reading, sometimes way low...and it seems like my mileage is worse when the temp gauge is reading low. Mechanic friend that worked on my vehicle a while back says my temp sensor connector/wiring is the culprit (the sensor that is on the coolant neck above the fan area) and sometimes I wiggle it around, make sure its firmly connected and the temp does read more normal for a while. The connector is so oil and dry rotted (plastic) that it just doesnt seem to want to stay tightly in contact. I ordered a new sensor and will probably just hardwire it direct since I doubt I can find a new connector anywhere. Huh, I am confused how the gauge temp sensor/connection can cause drop in gas mileage. It only tells the gauge what the temp of the engine and does not impact the ECU so it does not dump additional fuel into engine? In anther words, why this sensor/connection has to do with gas mileage? Am I confusing the matter? Link to comment Share on other sites More sharing options...
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