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2005 Legacy 2.5i Wagon 4EAT; 2005 Forester XS 4EAT
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Discussion Starter #1
So, my aunt (68 years old) totaled her '01 Stratus coupe - minor accident.

After looking at many cars, we found an '02 Forester L 2.5 with 138k on it in extremely good condition. We're getting it from a friend of ours who owns a small car lot, and he's working with her on the pice (he might make $150 on it total). This little thing is amazingly peppy, solid and straight.

We're heading back out there today to do the paperwork, since the banks were closed yesterday. He put her on dealer tags in the meantime.

On her way home, the check engine light came on. The dreaded P0420...

I assured her it's most likely something minor, and I'll do the same things I did to my '01 VDC that seems to have solved the issue for me.

My question is, roughly where should the temp gauge be? Mine usually sits almost 1/2 way. This appears to be more on the cool side, closer to the 1/4 mark. Could this simply be a sticking or bad thermostat? If so, we'll look into getting one from the Subaru dealer, and make arrangements to have it installed.
 

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OBW H6 VDC, Tribeca, XT6
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most likely the 0420 code was there before and cleared before you bought it (or before your friend bought it at auction). it may even be one of the reasons it went to auction if the poor former owners got quoted a converter to fix it.

cardoc has an in depth thread about it. there's a litany of things that cause that code and they're engine performance related. best solution is to find the actual cause and address it. most mechanics won't do that though as it's a detailed process, they'll likely just throw a expen$ive catalytic converter at it...so you're at the whims of finding a good mechanic, which is rare for this issue, i actually don't know any mechanics that do what cardoc does. as i said cardoc has a detailed thread on how to properly find out what's going on if you can get a mechanic that will do it, that's the proper and best fix.

the cheap and improper fix is a $5 spacer in the O2 sensor. but why do that to such a new car?

Given the headgasket issues of that motor and the fact that it's from a used car lot - meaning they probably bought it at auction for cheap, and temp gauge questions....i'd be looking into headgaskets - have they been replaced or is there signs of external leaking underneath (that's the failure mode of the original OEM gaskets).
 

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2005 Legacy 2.5i Wagon 4EAT; 2005 Forester XS 4EAT
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672 Posts
Discussion Starter #3
Thanks. I'm well aware of cardoc's thread. I read it a couple of times to try getting to the route of mine.

The head gaskets are dry.

I'm going to start with what I've done to mine that seems to be working to keep my light out.
 

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06 OBW 2.5, 05 Forester, had 03 H6 OBW
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5,935 Posts
On my wife's '05 forester a tiny bit of crunge was under the radiator cap gasket, system was not building pressure.

Heat felt fine but the temp gauge was a little low, the mileage sucked, and the exhaust pipe was blacker than usual.

Did not seem to be pushing excessive coolant into the overflow tank.

New cap cleared it right up.
 

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'14 Subi OBW, '18 Subi Forester
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Dave, I read what you wrote, then spent the next last 20 minutes trying to get my head around it. From a cooling system engineering standpoint, it doesn't add up. But then I though about the oddball stuff they don't teach in school and maybe I figured it out.

Cooling systems are pressurized to 2 atm to raise the boiling point of the mix an extra 20' F or so above what the 50/50 mix alone would be (which is around 230' F unpressurized). Pressurization increases the density of the fluid slightly while suppressing vaporization, so probably changes the heat transfer capacity of the fluid slightly, but not significantly. So that's not it - that would be the opposite of what was happening.

With no pressure cap (remove the lower seal and keep the upper one so that it flows into the overflow tank), you can drive pretty much normally under 90% conditions, and as long as the radiator and thermostat are sound, stay below the boilover point with no ill effects. Monitor the digital temp sender output thru the OBD port, and all should look normal.

So what happened in your case? I'll bet that you had a thermostat partially stuck open. That little wax pellet in the base of the shaft below the spring was probably messing up. With the stat open, the car ran perpetually cold, and well below optimum. When you put on a new cap that sealed, you pressurized the system for the first time in quite a while. I'll bet the change in pressure squeezed and kicked that pellet back into working order, and for the first time in forever, you got back up to 200' F operation.

But getting back to the OP's issue - yes, if it is indeed running cold, you will have mixture issues and ultimate cat performance problems.
 

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06 OBW 2.5, 05 Forester, had 03 H6 OBW
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I dunno, fibber, this was in the middle of a road trip to poughkeepsie to see my wife's folks.

I just know all was not good, then all was good (including verifying the thermostat opened the next day starting from a cold start).

I don't think the thermostat was stuck open, the heat was fine and the temp gauge was only just perceptibly low, and the car seemed to warm up as quick as normal.
 

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2001 VDC/SC One of a Kind
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14,318 Posts
So, my aunt (68 years old) totaled her '01 Stratus coupe - minor accident.

After looking at many cars, we found an '02 Forester L 2.5 with 138k on it in extremely good condition. We're getting it from a friend of ours who owns a small car lot, and he's working with her on the pice (he might make $150 on it total). This little thing is amazingly peppy, solid and straight.

We're heading back out there today to do the paperwork, since the banks were closed yesterday. He put her on dealer tags in the meantime.

On her way home, the check engine light came on. The dreaded P0420...

I assured her it's most likely something minor, and I'll do the same things I did to my '01 VDC that seems to have solved the issue for me.

My question is, roughly where should the temp gauge be? Mine usually sits almost 1/2 way. This appears to be more on the cool side, closer to the 1/4 mark. Could this simply be a sticking or bad thermostat? If so, we'll look into getting one from the Subaru dealer, and make arrangements to have it installed.
All Subaru thermostats operate in the same manner. Midway is operating temperature.

Yes, it would seem to be a thermostat issue which would cause a rich condition and abnormally high rear O2 readings which the ECM determines as poor catalyst efficiency.


Good synopsis Fibber2. :29:

GG, I see your starting to catch on. :gasp: :)
 

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2005 Legacy 2.5i Wagon 4EAT; 2005 Forester XS 4EAT
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672 Posts
Discussion Starter #9
Thanks! I'll start looking for an OEM thermostat and arrange to have it put in.

I'll make sure all the other stuff is done that I did to mine as well (fuel & air filters, clean PCV valve and Seafoam Spray for the throttle body).
 
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