So... My brother has a 98 Legacy, I believe its an EJ25.

 

Bare with me, there is a lot of random symptoms/info here.

 

Occasionally it overheats, so I looked at it. Its spitting out trouble codes P0480 and P0483, which are both fan related. Fans seem to work fine, while watching them.

 

With my scanner, I watched the temp rise (the defrost was on), the fans (and ac compressor) would come on for about 30 sec then turn off. And the temp continued to rise. At 215F I turned off the defrost and the temp returned to 185F. What? Thermostat opened? Extra load eliminated?

 

Weird thing is, when its running hot the coolant doesn't 'seem' to be flowing... Top radiator hose hot, low cold. I can open the radiator cap even when hot, which seems no pressure. I can put my finger in the coolant and its merely cool or lukewarm.

 

Haven't drained to check thermostat, but he says it was replaced 'last time.' Radiator cep he hasn't replaced.

 

So... (In order of my personal unprofessional opinion and economical preference)... Rad cap? Clogged radiator? Failed pump? Thermostat?

 

Head gaskets... I have but didnt use a compression/head tester due to the apparent lack of coolant flow. But theres no bubbles in the coolant reservoir. I dont thinknot will tell me anything.

 

All input appreciated. Thanks all.

Thermostat is my first thought.

That has to be a high quality or OE Subaru thermostat. The cheapos cause problems just like this.

Ya, not sure what is in there. Was my first thought too.

Replacing the rad cap may help as well.

Sounds good to start with thermostat and rad cap. These radiators can get blockage as well.

 

Those EJ25s are temperamental and known for head gasket failures. (Double check on the motor. If it's a legacy L or LS it would be EJ22. Not likely to have head gasket issues. Legacy GT or outback will be EJ25 and has frequent head gasket issues.) The simple check is to make sure that the coolant is full, look inside the coolant reservoir with the motor running and look for bubbles. Rev it if need be. No bubbles and the head gaskets are probably fine since these almost always fail in the same way. If you have bubbles you can do head gaskets or the longer term solution is to replace with a 1990-1998 EJ22 (Lots of write ups on swapping them in. Easy job. 1995 is the magic year)

 

But hopefully just thermostat or something simple

fans, rad cap, thermostat, coolant leaks, make sure the overflow hose isn't clogged or resting against the bottom of the overflow tank/preventing flow.

get all that easy stuff out of the way. 

boil the thermostat and i think shops can pressure test a rad cap. 

 

headgaskets are definitelyl possible.

compression test is pointless. 5 gas analyzer of the coolant or pressure test the cooling system is better.  the chemical tests sometimes work and you can DIY those.  but they're not as accurate as the analyzers. 

 

i've yet to ever see a failed tstat or radiator cap - many dozens of times i've hoped it was that and it never has been.  they're super easy and cheap to replace so they're a great starting point.

 

 i think they're failure rate is skewed by the number of people that have seen symptoms go away after replacing - when really it was an air bubble, or the symptoms returned later anyway - thereby mis-confirming the success of the original repair. 

Start with the radiator cap as it is definitely bad.  If it was good, you would have pressure.  Most of the time, that is the cause of overheating especially when going uphill.  It is cheap and easy so do it first and see if that solves the problem.

if you have no flow in the radiator when hot that would be the thermostat. sounds like its starting to open late due to deformed spring

So, we drained the coolant and looked at the thermostat. It was some Napa special or sumpin, flushed, replaced with oem, refilled coolant, bled it for a while, etc. Right at about 175 degrees F the thermostat seemed to open and the flow def picked up through the system (via watching the bleed funnel). The lower hose def warmed up after that. So coolant flowing problem solved.

 

No pressure: this one pretty sure the rad cap is indeed not holding pressure. Looked like there was guck, so i scraped it with my fingernail and it seems bumpy with a thin layer of neoprene or something that scrapes off, making it less believable that it will hold pressure, Told him to replace, but he has yet to.

 

Fan: I noticed that the main fan wasn't on at 185degrees. Shoukdn't it? I wouldn't think it would wait for much higher than that. Both fans kick on with ac.

 

Also found that with the ac running it held a steady 85 degrees, instead of creeping higher and higher like it used to. Thats a plus. I would still like to see that main fan kick in on its own though.

 

Anyone know the exact temp the ecm will turn in the main fan(s)?

 

Thanks to everyone for your input!

I don't know the Subaru specs, but most vehicles turn on the fans at 205, some higher.  Many vehicles have two temp settings to kick the fans on, 205 with the engine running, 210-212 engine off if the temp spikes within 10 minutes of engine shut down.  This is to remove residual heat from under the hood to prevent or reduce the damage to the oil trapped in the engine.  That trapped oil gets much hotter that the oil when it is running and is actually the biggest contributor to oil breakdown.

Thx, Keith. I remember watching my own Subie 2002 Legacy cycling around there but wasn't sure the correct numbers. Thx.

Usually 204F is the turn on temp, 194F is the turn off temp.

 

Thermostat begins to open at 174, but won't be full open til about 192 IIRC.

Normal running temp should be around 190-195.

Great info. Thx.