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I have a 2000 Subaru Outback. I keep regular maintenance on it. I'm very picky about my car, so everything gets done at the exact mileage each part or fluid change needs replaced. I deliver mail for the USPS out of my sub and recently, I started having an issue with my temp gauge slowly climbing, but only while parked after running it for about an hour. It normally stays right at 9:00 and the fans kick on if it even starts to think about moving. But a few days ago, I happened to be stopped at a box and noticed my temp needle climbing to the next mark on the temp gauge. But while I'm driving at any speed, my car stays cool and the needle doesn't move. It's currently averaging about 20F where I live. I thought maybe it was dirty and due for a flush and a change; the car has about 300,000 on it.

So I flushed it, multiple times with water, replaced the thermostat, replaced the coolant with Peak 50/50. Made sure there was no air in the system, checked for HG issues and I still have the problem. I did notice if I run my heater on max fan and max heat, the gauge never moves no mater if I'm idle or driving. The heater is hot and I have no other issues. Could this be a faulty temp gauge sensor or engine sensor?

I have asked every mechanic I could find and no one could figure out what is wrong. One person did suggest that I buy an actual Subaru Thermostat and put in the Subaru conditioner. I currently have a Duralast oem170f Thermostat in it and it's the same one I used about 2 years ago when I replaced it. The radiator is in good condition and I have no leaks in the hoses.

Any input on this would be appreciated.
 

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thermostat in these has to be a OEM, or a Stant Exact Stat in a pinch.

subaru coolant conditioner is nice to keep minor leaks sealed and rubber supple. ( at only 4.4 oz vs. the 2 gallons of rad fluid, its not a heavy duty sealer like the miracle clogging junk though).

and only a OEM rad cap. (no subs on rad cap, as it vents at the right kpa pressure vs. too tight or too loose like aftermarkets that measure in psi).


(above are really cheap as they go on many subarus over many years, amazon has real subaru dealers and makes it cheap vs. going to a subaru dealer counter and getting ripped off for the connivence of walking in.).

_____

you might rinse off the radiator if you have not already done so. (old bugs, and road dust really do add up overtime).

however, from your description it seems like the rad fans are not spinning fast enough,...and maybe the stat you got is not doing exactly what a OEM would.

@plain OM might be able to quickly link something for a 2000 H4 and testing how the fans should function.
 

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Thinking cruddy exterior radiator limiting cooling effect causing warmer running temp.

Water pump OEM only was it replaced at the last TB job?
 

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I started having an issue with my temp gauge slowly climbing, but only while parked after running it for about an hour. It normally stays right at 9:00 and the fans kick on if it even starts to think about moving.
As it should be; I like this!

But a few days ago, I happened to be stopped at a box and noticed my temp needle climbing to the next mark on the temp gauge.
Were both radiator fans running at high speed at that point? Any possibility they weren't/aren't, or only one is running? There's some fuses and relays involved.

I thought maybe it was dirty and due for a flush and a change; the car has about 300,000 on it.

So I flushed it,
Was the coolant dirty? Did you find flushing it multiple times resulted in progressive improvement?

Overall, the symptoms, especially the effect of the heater fan, might suggest the possibility of a clogged radiator, as has been suggested, either externally, or internally.
 

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Discussion Starter #5
Thinking cruddy exterior radiator limiting cooling effect causing warmer running temp.

Water pump OEM only was it replaced at the last TB job?
The radiator externally is clean. There was nothing coming out out when I flushed it, other than green coolant. The water pump was replaced with the timing belt about 16k miles ago.
 

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No, it was clean. No dirt, no anything. However, I was just outside checking the car and I noticed that when I first started it and when the car starts to reach optimal temperature, I hear the the thermostat clicking, but multiple times like it keeps opening and closing over and over.
 

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Is your reservoir tank getting fuller and fuller while the level of your radiator getting lower and lower?

If so, maybe replace the radiator cap and check the fittings on your hoses.
 

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My res-tank is very slowly disappearing. Filled it right to the full line a week ago and about a half inch is missing. Also, I believe it may be an HG after all. I was talking with a local guy at Auto Zone earlier and he told me to check the the res tank while it was doing the over heating and I did. I can see what looks like ripples in the coolant. But it's not bubbles. It looks like it's pulling the coolant from the res tank when it's overheating.
Could this still be a HG issue, or something else?
 

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I started having an issue with my temp gauge slowly climbing, but only while parked after running it for about an hour. It normally stays right at 9:00 and the fans kick on if it even starts to think about moving.
As it should be; I like this!

But a few days ago, I happened to be stopped at a box and noticed my temp needle climbing to the next mark on the temp gauge.
Were both radiator fans running at high speed at that point? Any possibility they weren't/aren't, or only one is running? There's some fuses and relays involved.

I thought maybe it was dirty and due for a flush and a change; the car has about 300,000 on it.

So I flushed it,
Was the coolant dirty? Did you find flushing it multiple times resulted in progressive improvement?

Overall, the symptoms, especially the effect of the heater fan, might suggest the possibility of a clogged radiator, as has been suggested, either externally, or internally.
While in my garage cleaning up, I started my car to check out the transmission fluid, my car started to overheat after about 20mins. But this time it got really hot and my fans were not coming on. So I immediately shut off my car and checked the fan fuses. Both of them were blown. Now I'm thinking it has something to do with the engine temp sensor and fans.
 

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. . .when the car starts to reach optimal temperature, I hear the the thermostat clicking, but multiple times like it keeps opening and closing over and over.
The thermostat wouldn't (normally) click, and with the engine running I tend to doubt it could be heard (especially in the cabin) even if it did for some odd reason. (The movement of the thermostat valve is controlled by a wax pellet that expands and contracts relatively slowly. The valve does not snap open and closed.)

Perhaps what was being heard is a relay, but we would need more detail as to where the sound was coming from to try to narrow it down. (If the HVAC was set to a defrost position, and the heater fan was not at Off, the AC compressor might have been cycling -- that would be a distinct click/clunk from the same general area on the front left side of the engine compartment.)

While in my garage cleaning up, I started my car to check out the transmission fluid, my car started to overheat after about 20mins. But this time it got really hot and my fans were not coming on. So I immediately shut off my car and checked the fan fuses. Both of them were blown. Now I'm thinking it has something to do with the engine temp sensor and fans.
So, can we go on the basis that since the overheating first appeared, it's possible that either one or both of the fans were not working?

The temp sensor is not likely a cause of the fuses blowing. The sensor itself doesn't control the fans; it only sends coolant temperature data to the ECU; the ECU in turn determines whether or not the fans are needed to maintain proper engine temperature and, if they are, it's the ECU that turns on the fans.

Fuses blow because of an overload in the circuit that the fuses are meant to protect, i.e., the circuit downstream of the fuse. In the case of the radiator fan fuses, that's the wiring to the fan motor relays and the motors themselves. The relays are controlled by the ECU, and would not themselves cause shorts. Also, there's two fans, two relays and two fuses. It's not likely that both relays would fail in the same way to cause the fuses to blow.

Perhaps the fan motors are failing. With DC motors, if the motor bearing is seizing, or for some other reason the motor might not start to turn rapidly (as it should) as soon as power is applied. As a result, the current through the motor can be excessively high, and that could blow the fuse.

With the ignition Off, the fan blades should spin freely when pushed by hand. Do they? With the 20 Amp radiator fan fuses replaced, engine warmed up and running (but not overheating), if the AC is turned on, do the fans run? (The fans should run when the AC is working and the ambient temperature is above freezing.)
 

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Have you used an infrared temperature gun to rule out an issue with the gauge or sensor?
 

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Discussion Starter #13
. . .when the car starts to reach optimal temperature, I hear the the thermostat clicking, but multiple times like it keeps opening and closing over and over.
The thermostat wouldn't (normally) click, and with the engine running I tend to doubt it could be heard (especially in the cabin) even if it did for some odd reason. (The movement of the thermostat valve is controlled by a wax pellet that expands and contracts relatively slowly. The valve does not snap open and closed.)

Perhaps what was being heard is a relay, but we would need more detail as to where the sound was coming from to try to narrow it down. (If the HVAC was set to a defrost position, and the heater fan was not at Off, the AC compressor might have been cycling -- that would be a distinct click/clunk from the same general area on the front left side of the engine compartment.)

While in my garage cleaning up, I started my car to check out the transmission fluid, my car started to overheat after about 20mins. But this time it got really hot and my fans were not coming on. So I immediately shut off my car and checked the fan fuses. Both of them were blown. Now I'm thinking it has something to do with the engine temp sensor and fans.
So, can we go on the basis that since the overheating first appeared, it's possible that either one or both of the fans were not working?

The temp sensor is not likely a cause of the fuses blowing. The sensor itself doesn't control the fans; it only sends coolant temperature data to the ECU; the ECU in turn determines whether or not the fans are needed to maintain proper engine temperature and, if they are, it's the ECU that turns on the fans.

Fuses blow because of an overload in the circuit that the fuses are meant to protect, i.e., the circuit downstream of the fuse. In the case of the radiator fan fuses, that's the wiring to the fan motor relays and the motors themselves. The relays are controlled by the ECU, and would not themselves cause shorts. Also, there's two fans, two relays and two fuses. It's not likely that both relays would fail in the same way to cause the fuses to blow.

Perhaps the fan motors are failing. With DC motors, if the motor bearing is seizing, or for some other reason the motor might not start to turn rapidly (as it should) as soon as power is applied. As a result, the current through the motor can be excessively high, and that could blow the fuse.

With the ignition Off, the fan blades should spin freely when pushed by hand. Do they? With the 20 Amp radiator fan fuses replaced, engine warmed up and running (but not overheating), if the AC is turned on, do the fans run? (The fans should run when the AC is working and the ambient temperature is above freezing.)
I'm gonna go check the fans in just a bit. But perhaps this could be a wiring issue? I recently had the hazard switch and switch connector go bad and I purchased a used connector on ebay and a brand new switch as well. I wired the new connector after cutting the old connector out and replaced the old switch. My hazard lights and signals work fine. When I cut the old connector, I disconnected the battery and cut 1 wire at a time and soldered back the same wire on the new connector. I made absolute sure that I didn't cross any wires and everything was secure before wrapping the whole harness in heat resistant electrical tape.
 

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Have you used an infrared temperature gun to rule out an issue with the gauge or sensor?
I don't own one, but I will see about getting one. Is there an alternative to measuring the temp without one until I'm able to get one? Also, where would the engine temp sensor and the temp gauge sensor be located?
 

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I'm gonna go check the fans in just a bit. But perhaps this could be a wiring issue? I recently had the hazard switch and switch connector go bad and I purchased a used connector on ebay and a brand new switch as well. I wired the new connector after cutting the old connector out and replaced the old switch. My hazard lights and signals work fine. When I cut the old connector, I disconnected the battery and cut 1 wire at a time and soldered back the same wire on the new connector. I made absolute sure that I didn't cross any wires and everything was secure before wrapping the whole harness in heat resistant electrical tape.
I doubt the rewiring of the hazard switch would result in a fault that blows the rad fan fuses. As far as I know, there's no rad fan-related wires up under the dash where the hazard switch is located, and, in any event, it sounds as if you followed a good approach when transferring the switch connector wires.

The engine coolant temperature sensor is on the back of the water pipe that bridges across the top of the engine block. See attached.

Although it's possible that the sensor is malfunctioning, I'm going on your earlier mention that "the fans kick on if it [the gauge] even starts to think about moving". That suggests the ECM, with the sensor input, is/was controlling the fans correctly. Of course, something might have changed . . .
 

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The fans were definitely working when this started to happen, but it seems like they are turning on at a higher and higher temperature and eventually it blows a fuse. What could possibly cause it to delay the fans turning on?
 

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Can someone give me a better pic of the 2 temp sensors? I'm not sure where the diagram is showing me.
 

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moved to gen2 section.
@Guardic you might want to hit the link next to the ? in my signature and type out that you got a 2000 H4.
...pleasantly with such high miles.

how many miles do you do on a regular day? how many hours is the car running?
 

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50 miles 6 days a week. Runs about 4 hours straight every day. I make 323 stops everyday too.
how much gasoline in gallons? and how much do "they" pay by the mile? (be it the USPS or the contractor). I think a old gen2 outback like this is great for postal.
 
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