Overheat at Idle

[HagarH]

1996 Lagacy LSI, "seems" to overheat at idle. The car has never "fully" overheated , never gone over 3/4 to 7/8 of the guage. Local mechanic thinks it is not really overheating. Temp never gets over 215 to 220 F. fans do kick on, cool and go off, replaced thermostat, water pump seems fine (flowing), replaced sensor at water exit on top the block. He also doesn't think it is the head gaskets though this is a known problem. Again the car doesn't seem to be really hot (temp wise), with the cap off it never boils over. So.........what is it? I am going to replace the sensor again and make sure it is OEM. Mechanic thinks it "may" be the gauge , possibly the heater box leaking but unlikely. He would like to see more symptoms before he diagnoses anything. Anybody got any ideas?

[hitzkrieg]

You want to make sure that you use a genuine Subaru thermostat to completely rule it out. Work experience tells me that aftermarket thermostats will not work in Subarus 90% of the time or more. Also, there are two temperature sensors on the car, right next to each other - the small one underneath the one with the plug in wiring harness is for the gauge, the other is for the ECU. 21203AA030 should be the part number for the gauge sensor.

[HagarH]

In Hindsight and Second Look:

Saw both sensors, looks like I got the correct one for the guage. Does this also control when the fans come on?

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Ok I replaced one on the water outlet coming from the block.....did not see any other sensors. Looking online using that part number, the part looks like the one I replaced. Are there two of those? I did not see two in that water outlet housing. Might another be somehwere else? I will recheck.

[wtdash]

Maybe this pic helps:


Good read on the Subaru Cooling / Coolant system - LINK.

The coolant temp sensor (CTS) is the brown plug; the gauge reads from the single-wired sensor right next to it. IIRC, they are not connected, and work independently of each other. The CTS would connect to the ECU and control the fans. If you didn't change the CTS - do it now as they can cause issues.

Since this is the 2.5 and the HG is always suspect - until fixed w/the new OEM gasket, I'd check for bubbles/oily residue in the coolant overflow tank - tell-tale sign of HG failure.

GL,
TD

[HagarH]

Just ordered the correct sensor. Will replace and go from there.

[HagarH]

Forgot! Thanks wtdash for the confirmation photo . Yes I had to dig further when this was mentioned and appreciate the confirmation. Must be an older engine! Has about 80% less crap around it than mine!