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Discussion Starter · #1 ·
I have a '98 Legacy Outback that has what seems to be an odd cooling issue.

Short background: 1998 Outback 2.5L 190K miles.
I'm aware of the headgasket issues on the 2.5 but I'm not certain that my car meets all the symptoms.

Driving on the highway the car will stay cool, and the temp sensor will be at "normal". After I get off the highway to start to slow down on the off-ramp, the temp gauge will spike and pin itself at max hot. However, If I rev the throttle just a little bit, the gauge will immediately go back to the level position in no time at all. My car will also stay cool driving around the city. From what I understand it is the opposite if the headgasket is bad?

Parts I have replaced:

-Upper and lower radiator hose
-Theromostat
-Radiator
-Radiator cap
-Expansion tank hose

Is this in-fact a head gasket issue?
 

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Premium Member
2010 Legacy 3.6R Limited
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1,300 Posts
mmm the week of cooling issues...

Have you been able to make sure you've fully burped any air out of the system? Revving it up or keeping RPMs above the 1,500 range will churn the bubble through enough that it'll recover some of its cooling capability, but only just.

I can't speak too much to the specifics of the head gasket issues on those since I've got a 3.0L and it's a whole different beast. However, overheating is universally bad, and the cooling systems are very similar between these cars from what I've been able to tell.
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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26,851 Posts
hope you got a new subaru rad cap on that new radiator. no subsitute for the subaru OEM as it measures in KPA whereas the aftermarkets measure in PSI.

what thermostat is that ? (hopefully a OEM or a stant exact stat).

and I too hope it is just a airbubble acting up.
@idosubaru might recommend something else.

have the head gaskets ever been done on this before. 190,000 miles sounds like a long long time for a EJ25D,...and that is one engine that I might consider doing head gasket work on as a preventative measure,...
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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hope you got a new subaru rad cap on that new radiator. no subsitute for the subaru OEM as it measures in KPA whereas the aftermarkets measure in PSI.

what thermostat is that ? (hopefully a OEM or a stant exact stat).

and I too hope it is just a airbubble acting up.
@idosubaru might recommend something else.

have the head gaskets ever been done on this before. 190,000 miles sounds like a long long time for a EJ25D,...and that is one engine that I might consider doing head gasket work on as a preventative measure,...
 

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OBW H6 VDC, Tribeca, XT6
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Burping

Those symptoms would be indicative of too small of a cooling system - can't handle high loads (interstate).

Unclog the area in front of the radiator and the confessor fins to make sure enough air flow is getting to the radiator.

It sounds very familiar to headgaskets.

The symptoms are less than average but not strange.

Two gray areas:

Consistently maintain and monitor the radiator coolant level. Otherwise you get confusion between low coolant derived overheating and possible headgasket or other causative agents.

EJ25Ds are the worst engine Subaru ever made - at 20 years old there's a very good chance they've been replaced previously and replaced headgaskets tend to have more variance in failure modes.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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not necessarily 100% - but, the primary symptom of bad HGs is, blowing coolant into the overflow tank. Often to the point of blowing out of that tank too. Often, at idle, there will be bubbles of combustion gasses coming up through the radiator. In the this last case, the chemical block test (sold at parts stores) can often be conclusive.

are you losing coolant? do not trust the level in the overflow - you must monitor inside the radiator (safely!)

other issues with the cooling systems is, 'small' aftermarket thermostats, some aftermarket rad caps, clogged heater cores, clogged radiators, maybe issues with the little overflow tube leaking at the neck of the radiator or clogged/stuck to the bottom of the overflow tank, intermittent radiator fans.


 

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OBW H6 VDC, Tribeca, XT6
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Early EJ25D's were really hard to nail down, the hardest Subaru headgaskets to diagnosis sometimes. They could have overheating events separated by months back when they were still new. I use past tense on purpose as time has mitigated that somewhat.

Yeah look for bubbles in the overflow tank - during or immediately after an overheating event would be good times to check often - but you can check any time.

The chemical tests are decent starting point but aren't always accurate - false negatives are common with those. An exhaust gas analyzer is more accurate but not common equipment.

They are random and can fail very sporadically at first. They progressively get worse and then you'll definitely know.
 

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Discussion Starter · #8 ·
System has been fully burped. I thought that might have been an issue early on but I've made sure there was no air in the system.

Thermostat and radiator cap are both STANT OE replacements. This issue prompted the replacement of all those parts so I don't believe they are causing an issue.

I did check for bubbles in the overflow tank, I did see some after driving on the highway. Does this confirm a headgasket? If so, I'd like to tackle it right away. Is it possible to tell which side is bad?
 

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I own 4 Subarus. A 95,97,02 and a 14. The first two are 2.2 and the last two 2.5.
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657 Posts
yea, the bubbles in the overflow tank are pretty definitive. You can't tell which side is leaking, but it doesnt matter. You need to replace both sides. Alternatively, replace the motor with a 2.2. Or junk it depending on the amount of rust or whether you can do the work yourself.

If it was just an external oil leak, you could keep driving until the leak gets too big to ignore. However, serious overheating is pretty serious and probably dangerous since the motor could eventually fail in traffic.
 

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Discussion Starter · #10 ·
Time to tackle a DIY. Better with the engine in or out? I've seen both but if you guys have some input i'd appreciate it
 
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