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Premium Member
2004 FXT 5MT
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48 Posts
Discussion Starter · #1 ·
I got my Fozzy in September '17 and starting having this bizarre issue where the engine heat sensor goes from normal temps, to almost in the red, and then sometimes the needle is all the way as far as it can go. And then a moment later it's back to the mid-line. I talked to a Subaru specialist shop and he said it could be an air bubble in the coolant or the head gasket, although if it was the head gasket it should be overheating all the time. What else could it be?
 

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I think its pretty difficult to be this confident about a diagnosis with as little information as is offered here. I have experienced these exact symptoms and the thermostat was not to blame. Tracking down overheat issues can be tricky, and in my experience: people seem to go to the thermostat first but that isn’t necessarily the issue. It is definitely a possibility but it is one among many.
 

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2008 forester XT 4EAT
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184 Posts
if it isn't happning all the time ,if he is not lossing coolant,if it get's hot than suddenly cool down so i think thermostat is the place to start and i believe it will solve it.
bubble it can be if you replace rad or flashed coolant ect... and didn't burped it.

Sent from my SM-G610F using Tapatalk
 

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2004 FXT 5MT
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48 Posts
Discussion Starter · #5 ·
Ok, an update.

I drove from Nashville to Houston yesterday and it was running warm to hot the entire time. Not ideal but didn't have a choice. Anyway, checked the coolant tank and it looks pretty bad, like black sludge. It was also bubbling the first time I checked it so there was/ is probably air in there.

Recently I had done a lot of work to it, and the mechanic filled the overflow reservoir with orange type coolant. It didn't need to be filled cuz now the coolant is way above the fill line and looks nasty. But so now I'm also not sure if it was this which caused it, or if it's my HG...

What do I do from here?? Thanks Moshe for the suggestions
 

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Premium Member
2004 2.5 XT Premium 4EAT
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1,376 Posts
Yay go team. Mine is apparently having a head gasket issue with similar symptoms. Mechanic didn't want to go straight to head gasket. We did thermostat and pressure caps but no success. Coolant will boil in the plastic reservoir to the right of the radiator. Over heat on a two hour drive, but two days later no temperature change on a three hour drive. Hydrocarbons not present in the coolant during tests. It's been a blast trying to diagnose.

In any case, hopefully your result is better than mine. Rootin for you.
 

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Premium Member
2004 FXT 5MT
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48 Posts
Oil seems fine color wise but was low, which is weird because I had it replaced only 1,000 mi ago. About a month. Put in the the remainder of my T6 I have laying around.

Edit: nvm dipstick was just being retarded, so now I'm a half a quart overfull lol
 

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2004 FXT 5MT
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48 Posts
Discussion Starter · #9 ·
So is the thermometer/radiator tied to the AC compressor at all?? I had been without AC for most of May until I found my compressor wasn't fully plugged in. Then, just now, I noticed a sequence of events:

1. AC stopped working / was pumping room temp hot air
2. Engine thermo measuring very high, simultaneously
3. Battery measured at 12.00 volts on my turbo timer during this
4. In neutral, I revved the engine for about 20 seconds, boosting the voltage up to 12.9 from the alternator
5. I heard / felt the compressor kick on and right away the cold air started pumping and the temp went to normal again

Is it possible that this has all been related to my battery not supplying enough juice to the compressor? Way back when, I noticed that the higher my RPMs, the more likely the temperature was to go back to normal. So for example I'd notice the temps up, then switch to a lower gear and suddenly it'd drop.
 

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2004 FXT 5MT
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48 Posts
Discussion Starter · #10 ·
Bump. This problem is driving me nuts because I'm not sure if I should worry about it being something serious like HG or radiator problem.

For a long time the symptoms turned into this: my car would start, the compressor would do a long squeal, and the AC would blow cold. About 5-10 mins into driving the AC would cut and the temp would go all the way up. If I stayed at 5K+ RPMs for a little while, the compressor would do a short squeal, kick on, and everything back to normal. When it was cold outside the compressor wouldn't kick on at all and the temp would be all the way up for the entirety of my drive.

A month ago I had the compressor replaced alongside my timing belt, and threw in a new thermostat and accessory belt while doing that. For about 1K miles I never saw any other random "overheating" till yesterday. I did notice my (new... chinese) compressor squealed again - once, and briefly - yesterday in 30F weather. Symptoms were different this time. Temps would jump to hot but not all the way and then back to normal.

Is there any way that faulty wiring could cause bad thermostat reads? Am I going crazy? Where did I go just now?
 

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Premium Member
2004 FXT 5MT
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48 Posts
Original problem: AC isn't working consistently (on for 5-10 minutes and then off). Sometimes the engine runs hot when AC is ON only.
Checklist:
  • AC charged correctly, 40 L 200 H
  • Compressor new from 2yrs ago (eBay aftermarket)
  • Thermostat new from 2yrs ago
  • Drier possibly bad
Yesterday's work:
  • Replaced condenser & drier
  • Replaced radiator with Mishimoto 3 row aluminum
  • Replaced high pressure and low pressure valves
  • Replaced compressor O-ring
  • Re-charged all freon back to 40 L 200 H
  • Swapped around AC and fan relays
  • Thought maybe fans weren't running high enough
New problem:
Now the AC blows cold pretty consistently, except now the engine thermostat reads to the redline after driving for a while, and then the AC goes warm. If engine is cool AC is cool. I drove it for 20 miles this morning and it the AC was OK and the engine stayed cool. I tested again at noon and I couldn't make it down the street without the engine running redline. RPMs seem to influence engine temp reading. Fans were running high. Radiator is full and not boiling over, although I did see it boil in the overflow tank and spew some out. (I think from overfilling the overflow yesterday doing the radiator)

Today's work:
  • Call Subaru. Tech said to check for head gasket.
  • Checked head gasket using combustion leak test kit / hydrocarbon test on radiator. Blue liquid, no leak, head gasket OK.
  • Drove it to the shop (local private garage). Mechanic that lives there and I'm friends with says he thinks the fans aren't kicking on high enough or they're not blowing at full speed, but they were when I drove up. I was redlining driving in and AC had gone warm. These two did not used to be connected, like in backstory, but now they seem to be.
  • Changed the oil. I was at two quarts from a slow bleed valve cover gasket leaking over several months. 4.8 qts in now.
  • Checked the main radiator hose, it was not bursting at the seams and was not too too hot to touch despite redline temp reading.
Main problems:
Am I really overheating?
Why is the AC going out when the temp goes up like you'd expect?
 

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18,175 Posts
So is the thermometer/radiator tied to the AC compressor at all??
Now the AC blows cold pretty consistently, except now the engine thermostat reads to the redline after driving for a while, and then the AC goes warm.
Why is the AC going out when the temp goes up like you'd expect?
When the engine temp goes high the AC will cut out; just as it does with WOT.

Could be the water pump? What thermostat was used for replacement OEM or after-market? Seems OEM is the recommended option.
 

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Premium Member
2004 FXT 5MT
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48 Posts
Discussion Starter · #13 ·
But did I bleed the coolant/ burp the radiator? NO

I just did a couple hours ago with a no spill funnel. And I just drove an hour to another town with NO overheating and AC that had me shivering cold.

If it runs hot tomorrow in the sun then I will be scratching my head.

@Kevin
We thought about the water pump not circulating well but it isn’t leaking. Thermo iirc was aftermarket.
 

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2004 FXT 5MT
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48 Posts
Discussion Starter · #15 · (Edited)
Scratching my head today. It’s overheating again. I conducted a check before driving to Starbucks a couple miles away.

  • No milky oil
  • Overflow reservoir seems to have bubbled up again and made a nice green surprise on the radiator. Does that mean head gasket for sure? Am I putting too much in the overflow and when it expands it’s just too much to hold? Could that introduce another bubble?
Seems like if the sun isn’t out it’s okay. I drove in the early morning yesterday and then last night with no issues.

I think it may actually be overheating because of the AC aligning with engine temp. So this is not the same issue from a couple years ago, the temp does not go back down unless I stop the car for a while.

It really doesn’t seem like head gasket because:

  • No milky oil
  • No white smoke out of exhaust
  • Hydrocarbon test negative
  • Engine performance is good
  • No coolant leaks besides overflow reservoir bubbling
Not ruling out the water pump circulation but if it were wouldn’t it run hot always?

Yesterday 2nd test after radiator
541186


Combustion test
541187


Burp!
541188


Green surprise
541189
 

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Administrator
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18,175 Posts
Another member's recent overheating issue was identified as the thermostat. This was achieved by removing the thermostat and running the car without it. If the temp is OK then the issue is the thermostat; if not OK then the issue is the water pump or something more serious.

Also, from cold, open the radiator and start the car. As it warms up do you observe bubbles; can you see fluid movement?
 

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Premium Member
2004 FXT 5MT
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48 Posts
Discussion Starter · #18 ·
@Kevin
Can’t get to that right now since I left all my tools behind but will check. It’s very cloudy here now with the tropical storm coming through, no overheating for a trip to the store.

Here’s the radiator on cold start:
 

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Premium Member
2004 FXT 5MT
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48 Posts
Discussion Starter · #20 ·
@Kevin
No bubbles that I could see. I watched it for 20 minutes yesterday when I burped it and the only bubbles where at the beginning before it filled. I do think it’s not running AS hot as the needle says, because the main hose isn’t bursting or burning hot. So really could be thermo. Just odd that the AC goes warm.

I ordered a new OEM thermo along with timing belt and water pump (if I’m going to change the water pump, might as well...). Thinking about redoing the heads, maybe head gasket, since I’m in there.

btw, I remembered something we did a couple years ago when replacing the clutch. We put a bunch of red type coolant with stop leak in the overflow reservoir. I was bad at cars back then so had no idea. The reservoir tank had unbelievable gunk in it when we replaced the radiator a couple days ago. Could have got in the block.
 
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