Decreased fuel economy after installing transmission cooler

[hillbillyhans]

He must have taken his e-brake off!

[DM6156]

sorry for the delay, was doing a lot more driving mixed city/highway and strickly in town (under 45 mpg).

 

Problem has been "resolved" for about 9 tanks.

 

I found the sound damper (plastic) under the hood was just laying on the engine, not installed correctly. I actually fixed this prior to the trip from ga to nc.

 

This is why i said it was a silly "fix". Didn't make any other changes to vehicle (same oil since shop changed it, same tire pressure, same air filter, etc). Filled up prior to leaving on the ga to nc road trip at same gas station usually fill up at. Previous tank to this fill up from same station was in 15 mpg range. On the first leg of trip, saw over 23 mpg. Constantly saw over 22 on mostly highway driving (4 tanks). Saw over 19 on mixed (45% highway - 55% city). Mixed with < 25% highway in 17 mpg range.

 

Unless someone has a better explanation, I'm assuming it was a heat issue as the damper has room for air flow between it and engine when installed correctly. However, this was not the case with it laying right on top of engine.

 

I'm sure there are some that will blame gas, I'm not seeing that. It would have taken 5 tanks to get rid of the "bad" gas and just happened to get better when i fixed the damper and on the first tank of the road trip.

Edited May 3, 2012 by DM6156

[SchwarzeEwigkt]

It sounds like the battery was unplugged for a bit. I saw the radio presets and everything were still there, but maybe they unplugged it just long enough to reset the computer but not long enough to reset the radio? I did it by accident on my Legacy when I was installing the harness for my float charger. It was enough to blow away all the ODB monitors but the radio presets stuck. I only found out when I took it to get inspected.

 

5 tanks does seem like a awfully long time for the ECU to relearn, though. Perhaps a chunk of carbon got jammed in an O2 sensor and make lazy and thus richer than normal, then cleared out?

[Subaru_dude]

sorry for the delay, was doing a lot more driving mixed city/highway and strickly in town (under 45 mpg).

 

Problem has been "resolved" for about 9 tanks.

 

I found the sound damper (plastic) under the hood was just laying on the hood, not installed correctly. I actually fixed this prior to the trip from ga to nc.

 

This is why i said it was a silly "fix". Didn't make any other changes to vehicle (same oil since shop changed it, same tire pressure, same air filter, etc). Filled up prior to leaving on the ga to nc road trip at same gas station usually fill up at. Previous tank to this fill up from same station was in 15 mpg range. On the first leg of trip, saw over 23 mpg. Constantly saw over 22 on mostly highway driving (4 tanks). Saw over 19 on mixed (45% highway - 55% city). Mixed with < 25% highway in 17 mpg range.

 

Unless someone has a better explanation, I'm assuming it was a heat issue as the damper has room for air flow between it and engine when installed correctly. However, this was not the case with it laying right on top of engine.

 

I'm sure there are some that will blame gas, I'm not seeing that. It would have taken 5 tanks to get rid of the "bad" gas and just happened to get better when i fixed the damper and on the first tank of the road trip.

 

if even something this small and seemingly insignificant could make such a noticeable difference in fuel mileage, I wonder what could be done to the older, smaller subarus to increase mileage?? Looking at the kinds of computers used and tests performed to build a more modern vehicle like a Tribeca... I could see something like that making a difference.

[DM6156]

It sounds like the battery was unplugged for a bit. I saw the radio presets and everything were still there, but maybe they unplugged it just long enough to reset the computer but not long enough to reset the radio? I did it by accident on my Legacy when I was installing the harness for my float charger. It was enough to blow away all the ODB monitors but the radio presets stuck. I only found out when I took it to get inspected.

 

5 tanks does seem like a awfully long time for the ECU to relearn, though. Perhaps a chunk of carbon got jammed in an O2 sensor and make lazy and thus richer than normal, then cleared out?

 

I checked it out with my auto xray 6000 scanner. no lazy oxygen sensor. nothing seemed out of the ordinary, no pending codes either. Also, computer hadn't been reset in over 8,000 miles when i looked prior to making the "fix". based on milage, it would have been reset prior to me purchasing it.

 

I'm assuming resetting computer by unplugging battery would cause computer to log being reset, but maybe not.

 

I wish i would have saved the data or made notes, i'm curious about some of sensor data like air intake temp and coolant temp.

 

The tech that did the work at the local shop told me the subaru tech he spoke to doesn't even open the hood to install the transmission cooler, all the work is done from under the car. I can call shop tomorrow and see if they unplugged battery for any reason. I've been using this shop for several years exclusively. I recommend everyone i know to take their vehicles there.

 

The shop manager's dad used to run parts department for the subaru side of the dealership, he used to work as tech for the chrysler side.

Edited May 3, 2012 by DM6156

[SchwarzeEwigkt]

I checked it out with my auto xray 6000 scanner. no lazy oxygen sensor. nothing seemed out of the ordinary, no pending codes either. Also, computer hadn't been reset in over 8,000 miles when i looked prior to making the "fix". based on milage, it would have been reset prior to me purchasing it.

 

I'm assuming resetting computer by unplugging battery would cause computer to log being reset, but maybe not.

 

I wish i would have saved the data or made notes, i'm curious about some of sensor data like air intake temp and coolant temp.

 

The tech that did the work at the local shop told me the subaru tech he spoke to doesn't even open the hood to install the transmission cooler, all the work is done from under the car. I can call shop tomorrow and see if they unplugged battery for any reason. I've been using this shop for several years exclusively. I recommend everyone i know to take their vehicles there.

 

The shop manager's dad used to run parts department for the subaru side of the dealership, he used to work as tech for the chrysler side.

I don't know that there is any easy way to tell if the computer was reset once all the monitors go ready again.

 

I'm interested to find out what you learn there. I find it really hard to believe that a plastic damper really would cause that problem, but it that was it, that was it. I'm curious as to what the heck the thing was doing under there to make such a big difference.

 

The battery reset seems more plausible but really is just a theory.

[Subaru_dude]

just put that piece of plastic the way it was when you were getting worse mileage and see if it hurts your mileage again. Then put it back the way it's supposed to be, and see if it's back to normal!