Subaru 2.5 Overheating Issue

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This topic contains 14 replies, has 7 voices, and was last updated by Brandon Driskill Brandon Driskill 6 years, 11 months ago.

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  • #835552
    Nolan Gunn
    Nolan Gunn

    1999 Subaru Legacy Outback 2.5 – EJ25 Engine DOHC
    185k miles

    Bought my suby at 150k miles and at about 180k it started to overheat a few times (this is mid summer).

    First time was driving very slowly (5mph) on a back road when i noticed it overheating, i shut it off, opened the hood, and the overflow reservoir was overflowing with coolant (seemingly boiling). I Parked it for about an hour, came back and filled it with about 1/2 gallon of water to make up for the lost coolant. Drove it home without a hitch.

    A week later I drained the coolant (via the plug) put new coolant in and checked my fuses. The fan motor fuse had blown, bought a new fuse, now the fans work fine.

    Second instance was on a long trip. Drove 750 miles (split up over 2 days) there without a problem, then after about 600 miles of driving home, stopped at a drive thru and quickly overheated as it idled. Stopped, parked for about 5 minutes, then drove the next 150 without a hitch.

    3rd and last instance was when I decided to start the car and let it idle. After about 15 min it started to overheat slowly.

    Haven’t lost any power on hills, idles steady. ill be changing the oil soon, so ill be updating if i see any milkiness in the oil (HG).

    at 160k Timing Belt + Water Pump were done. So I’m assuming the water pump is fine.

    So i guess it only overheats when im idling or driving very slowly. Are there any tests to diagnose the issue? Chemical test the coolant? Flow test?

    The body and engine are in great condition, so i want to keep her for as long as possible, so im grateful for any help!


Viewing 14 replies - 1 through 14 (of 14 total)
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  • #835555
    A toyotakarl
    Its me

    You can do a coolant pressure test (pressure should hold) to find out if you have an issue with a head gasket or block… 2.5’s are known for bad head gaskets at around 100k intervals… (just do a Google search about head gaskets and the Subaru 2.5…. lots of info)


    Andrew Phillips
    Andrew Phillips

    [quote=”ToyotaKarl” post=143118]You can do a coolant pressure test (pressure should hold) to find out if you have an issue with a head gasket or block… 2.5’s are known for bad head gaskets at around 100k intervals… (just do a Google search about head gaskets and the Subaru 2.5…. lots of info)

    +1. If the coolant pressure test holds pressure as it is supposed to do, then maybe your pressure cap is just bad. Bad caps can cause overheats and loss of coolant.


    Change the cap and do a coolant pressure test as others have stated. If it’s inconclusive try a combustion leak tester:

    This will tell you if combustion gases are going into your coolant. If they are it is probably a head gasket issue as this engine is known for it up until 2005.

    Brandon Driskill
    Brandon Driskill

    The Subie EJ25s (aka 2.5L) during this time WILL have head gasket issues. It’s just a matter of time. The good thing is the factory has an updated gasket, multi-layer steel, that should fix it permanently. Get this repaired before you overheat this to the point of warping the head(s). They warp fairly easily from overheating.
    There are two types of engines, Phase 1 and Phase 2. Both variants can have head gasket problems associated with them, but the problems, how to diagnose them, and how to fix them, differ between the two phases.

    PHASE 1 (Dual Overhead Cam):
    Used in:
    1996 to 1999 Legacy Outback
    1996 to 1999 Legacy GT
    1998 Impreza RS
    1998 Forester

    Typical failure mode:
    Internal leak, not externally visible. May see bubbles in overflow reservoir, sludgy residue on walls of overflow reservoir, random overheating of engine.

    Covered by service bulletin: No

    Cost to repair:
    DIY: $200 parts
    Independent shop: $1000-$1500
    Dealership: $2000

    Phase 1 engines:

    Phase 1 engines typically experience an “internal” head gasket failure if failure happens. This is hard for a lot of mechanics to diagnose, is difficult to reliably duplicate, and often has resulted in the owners throwing money and parts at the problem. New thermostats, flushing coolant, new water pumps and radiators are examples which do not fix the problem if it is indeed head gasket failure. If the engine overheats too many times or too severely, it can result in warped heads and the need for a new engine. As of this date Subaru has never acknowledged the existence of any problem, and are unlikely to do so. They have redesigned the head gaskets and most people that have had the new gaskets properly installed have had good success. The “coolant conditioner” described in WWP-99 DOES NOT fix this internal leak, nor does it give you an extended warranty against head gasket failure. Headgasket replacement is your only option besides engine replacement.

    Common symptoms:
    Overheating, often when slowing or stopped after extended high load driving. The overheating can be seemingly random and sporadic.
    Bubbles in coolant overflow reservoir, immediately after running.
    Sludgy residue in coolant overflow tank.
    Hydrocarbons in coolant overflow tank, this is tested by a mechanic with specialized equipment and is not evident visually.

    Nolan Gunn
    Nolan Gunn

    Thanks for the input!

    I’ll be changing the radiator cap and thermostat today and will report back if anything changes!


    Andrew Phillips
    Andrew Phillips

    I wouldn’t change the thermostat just yet. But, if you go ahead and do it, make sure to get all the air out of the cooling system.

    Nolan Gunn
    Nolan Gunn

    Changed the thermostat and radiator cap, the old cap had some stuff on it that was on the gasket. Changed the thermostat, it opened up as it should into the bottom hose. I think I purged all the air, but I’ll run through what I did just in case…

    -Changed thermostat. (Drained coolant)
    -opened bleeder valve (left side has a Phillips head on it)
    -filled until bleeder overflowed
    -closed bleeder
    -started car
    -had a funnel filled with coolant filling the system.
    -ran at 2500rpm for about 10 minutes (had the heater setting on hot)
    -air bubbled out a bit then stopped after 10minutes
    -stopped the car
    -put radiator cap on, filled overflow, and went on my merry way

    -coolant looks pristine. Its been in there for a month and its not discolored, looks like the day I put it in.
    -oil dipstick oil looks normal

    Is there anything I’m missing in purging the air out? Next steps?

    Nolan Gunn
    Nolan Gunn


    Still overheating. Still loosing coolant very slowly. Overheated on a long trip, realized that coolant was low by maybe 1/2 gallon. Filled it, stopped again when it overheated again, filled it up again and went for 3 hours and never had an issue. Check the level the next morning and I only lost maybe a pint over those 3 hours of highway driving. Any ideas?

    BUT. When i changed coolant, everything looked pristine, like mtn dew. Also, when i changed the oil, no milkiness. It looked like every other oil change ive ever done.

    Other than Radiator cap, thermostat, etc. What else can i do? Radiator? Hoses?

    Also, if it does happen to be a bad head gasket, how do i check which side it is?
    And, can i do this without pulling the engine? Ive heard of people doing it, im pretty mechanically inclined, so i’m confident i can do it if it comes to it, but how long will it take? (i.e a weekend, a few days, etc.)

    Thanks for any input!

    Brandon Driskill
    Brandon Driskill

    Like I said earlier, I’m 99.9% sure that this is a head gasket. I understand you wanted to check all your bases, however this is such a common issue with this engine that it is recommended to change the head gaskets to Subaru’s updated Multi-Layer Steel gaskets even if you have yet to have an overheating issue.
    You can have a shop do a test to check for exhaust gases in the coolant to verify the issue.
    If you want to tackle this on your own, there are videos on YouTube (the one by South Main Auto Repair is very detailed). Also, as far as removing the engine vs not removing the engine, both ways work, it’s just a matter of preference. Removing the engine seems like more work, but it is a method to get the cylinder heads off and back on easier and faster. Leaving the engine block in keeps you from having to have a few more tools/engine stand/hoist, but takes a bit more wrestling with space in the engine bay.
    Also, please change BOTH gaskets as the both will leak even if only one is leaking now.
    I would allow 1 week minimum to do the work. This is due to having to have the heads surfaced. Since the car has already overheated, the heads will no longer be level.

    EricTheCarGuy 1

    Head gaskets are a very common failure on that engine as pointed out. I cover the test for head gasket failure in this video.

    If you do find a combustion leak, you won’t know which side. You do them both as a general practice. Briansmobile1 has a good video series on this.

    More information on diagnosing overheating problems.

    Good luck and keep us posted.

    Nolan Gunn
    Nolan Gunn

    One more question,

    I found this coolant leak using a UV dye kit. ^ it’s leaking coolant, and i had noticed on the trip a few days ago it dripping a little. What is this gasket and what function does it serve? Thats the timing cover and the valve cover i believe.


    2006 and newer Subarus have headgasket problems too.Cause of an oil leak too,seen this in a 2007 Subaru oil leaking from the headgaskets with just over 100,000 miles today.Best way to do the headgaskets is pull the engine out completely and don’t reuse the old headbolts.Buy new headbolts since they are torque to yield headbolts

    Nolan Gunn
    Nolan Gunn

    Hey all! I bit the bullet and went ahead and did the head gaskets.

    I replaced the head gaskets (and many others, cam seals, valve covers, etc) while i was in there.

    Had the heads resurfaced, the shop said they were pretty warped. So got those done for $150 total.

    One recommendation: Schedule a time with a machine shop, don’t just walk in. I brought mine in and got them 6 days later, which is totally fine because i gave no prior notification. But for future reference, if you want it done quickly, schedule a time in advance.

    Another thing was i didnt pull the engine. I left it in and didnt have too many issue. The only difficult bolt to get to was the 10mm bottom right driver-side valve cover bolt. Also had trouble with the cam sprockets, those were tough. But i rigged up a strap wrench and got them loose.

    So in total it took approximately 4 days of labor (24ish hours) plus the days the heads got machined. like i said before, i couldve gotten it done faster if i had scheduled the machine shop ahead of time. But anyhow, i got it done.

    Cost was approx
    – $140 for the gasket set
    – $150 for heads machined
    – $60 in random tools
    – $50 in replacement fluids


    Thanks for all the input! And thanks to eric (and brians mobile1) this 19 year old tore apart a whole engine!

    Brandon Driskill
    Brandon Driskill

    Thanks for the update. Best wishes on years of trouble free motoring.

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