Puzzling overheating event

[spud]

I recently took my ~170k mile 97 Legacy Outback wagon (automatic transmission) for a weekend road trip and experienced some puzzling overheating of the engine. (Not sure if this should be posted in the repair forum?)

 

While driving a mostly gentle but sometimes rolling descent for about 25 miles I used 3rd gear sporadically to control speed (which fluctuated between 25-50 mph). I had the a/c running on low. The outside temp was in the mid to high 80s. I encountered a 5-mile-long, ~5-6 % grade where I sometimes used the engine as a brake and proceeded at about 20-30 mph. At the bottom of the grade, I noticed my temperature gauge was redlining and I immediately turned on the heater full blast and pulled over. (I realized that I was so focused on the descent and traffic that I had not been vigilant about monitoring the gauges for the past 30 minutes.) The radiator overflow tank was full and bubbling mildly over. Only one of the two radiator fans was spinning (the right-hand one). I let the car idle on level ground with the heater on full blast and in 15 or so minutes the temperature gauge read normal. The radiator overflow tank was now empty because presumably the coolant had been drawn back into the radiator as it cooled. I turned the car off and then back on again and observed that the other radiator fan (the left hand one) was now spinning and the right hand one was now idle. I added about 8 oz of coolant I happened to have in the car. I then drove the remaining 130 flat highway miles back home with the a/c off in temps of 75-80 degrees and had no overheating. I have since driven the car around town with no issues and observed that both radiator fans spin.

 

Before I left for the trip I had the valve cover gaskets and covers, spark plugs and wires, and belts replaced. It seems odd to me that the car would overheat while descending in warm (not hot) weather, even if the a/c were on and the engine was serving as a brake. Any thoughts?

[bstone]

Bubbles in the radiator? You know what I'm thinking.....

 

When were the head gaskets replaced last time? Did they use OE HGs to replace them with or an aftermarket brand?

[Rooster2]

There is more than a good chance that you have a head gasket going bad. All 96-99 Subies with the 2.5 motor are prone to this problem. I have read that the problem frequently starts out like yours, it over heats, then is okay for a while, then over heats later. The "laters" then become more and more frequent.

 

In a Subie, when the head gasket goes bad, it allows exhaust gas to enter the cooling system, which causes the engine to over heat. The exhaust gas exits the motor through the radiator over flow hose in the reservoir. The exhaust gas and over heated coolant then spew out of the reservoir, so you find the reservoir empty.

 

If the motor over heats again, check the radiator reservoir. If bubbles are present in the reservoir, then it is guaranteed to be a bad head gasket.

 

I recently saw all of this first hand, when my wife drove our 98 OBW home all super hot and bothered. Yes, it blew a head gasket, and my wife drove on. "Thanks Dear" for just cooking the motor. I am still in the process of finishing the details of having a used motor put in the car.

 

I am not real happy with Subaru for not having a better warning system to tell the driver that the motor is over heating. Sure, the gauge is fine, but it would have been much better to have a flashing warning light added to the gauge, as well as to have the check engine light come on, when the engine over heats. It is just too easy to not notice the position of the needle in the temp gauge.

 

For now, I suggest when you drive your Subie, that you watch the temp gauge like a hawk. If the temp needle climbs to HOT, pull over, and let the motor cool down. That was smart of you to turn on the heater, when you noticed the motor over heating. That does help drain heat from the coolant.

[1 Lucky Texan]

if you're lucky, your mechanic left an air bubble in the system and MAYBE not much damage was done by the event.

 

Or headgaskets if you're unlucky.

[MilesFox]

You may have a bad thermosensor for the main fan that cmes on with a certain temp. the other fan comes on with the AC.

 

The AC may have just heat soaked and caused an acute overheat.

 

Suppose the radiator is becoming inefficient to age and corrosion. Alo, at that mileage, the WP may becoming inefficient if it is the original one from new. As a old water pup will want to seize and then take the timing belt with it.

 

I would say, if you had a HG problem as described above, you would be having this symptom more often in more varying conditions.

 

It would not be a bad idea to replace the radiator if you intend on keeping your car for the next 100,000 miles.

[porcupine73]

The fans operate according to a control chart, something like this one though it isn't for your specific year.....

 

[The Dude]

Spud, have the coolant tested for exhaust gas. It's quick, easy, and relatively cheap. That way, you know for certain what is going on with your engine. Don't play with this, overheating is very bad for your engine. You could warp the heads or even lose the entire engine.

[3Pin]

Sounds like a HG. Get it good and warn and check for bubbles in the overflow tank. If you have bubbles, a HG replacement is in your future.

[nipper]

Bubbling overflow tank means only one thing, a head gasket.

[spud]

Thanks to all for your thoughts-I know there is a lot of head gasket discussion on the USMB but this seemed a little atypical. This car has been in our family since 11K miles and it has served us very well--never overheated until recently and I don't believe ever had any HG issues. It is at the mechanic getting checked out right now, diagnosing stuff like this is beyond my ability. I did see bubbles in the overflow tank when I dropped it off though...

[Rooster2]

Thanks to all for your thoughts-I know there is a lot of head gasket discussion on the USMB but this seemed a little atypical. This car has been in our family since 11K miles and it has served us very well--never overheated until recently and I don't believe ever had any HG issues. It is at the mechanic getting checked out right now, diagnosing stuff like this is beyond my ability. I did see bubbles in the overflow tank when I dropped it off though...

 

Bubbles in the overflow tank is an absolute dead give away of a bad HG in a Subaru. Standard HG tests on other cars, is to look for oil/water mixture on the oil dip stick, and do compression test. These tests don't work on a Subaru. I hope your mechanic knows that. If a new head gasket is needed in your future, be sure to use an OEM Subaru HG. Other aftermarket HGs just won't hold up for long.

[bstone]

Bubbles in the overflow tank is an absolute dead give away of a bad HG in a Subaru. Standard HG tests on other cars, is to look for oil/water mixture on the oil dip stick, and do compression test. These tests don't work on a Subaru. I hope your mechanic knows that. If a new head gasket is needed in your future, be sure to use an OEM Subaru HG. Other aftermarket HGs just won't hold up for long.

 

Can he try some coolant conditioner?

[spud]

bstone,

2 years ago my mechanic put BG Super Cool Conditioner (universal) in when they flushed out the coolant and replaced it.

 

What sort of cost should I expect to replace the head gaskets, assuming no damage was done from the overheating? (This sort of repair work is well beyond me.) Does it need to be done by a person experienced with Subarus?

[bstone]

bstone,

2 years ago my mechanic put BG Super Cool Conditioner (universal) in when they flushed out the coolant and replaced it.

 

What sort of cost should I expect to replace the head gaskets, assuming no damage was done from the overheating? (This sort of repair work is well beyond me.) Does it need to be done by a person experienced with Subarus?

 

I think you mean this product:

 

BG 546

BG Universal Super Cool®

BG Universal Super Cool® coolant additive is specially formulated for use in conventional, long life, hybrid and heavy duty coolants. It provides outstanding protection for all metals utilized in modern automotive cooling systems. It has excellent corrosion inhibitors, anti-foam capabilities, and is biodegradable in its unused form. Passes ASTM 2809 and ASTM 2570 in ASTM reference synthetic used coolant.

Source: http://www.bgprod.com/products/coolingsystem.html

 

It probably didn't help or hurt. I have to admit, tho, I never put these things when doing a radiator fluid change.

 

The cost you're looking at is probably around $1500, give or take a few hundred depending on the shop and where you are. The chances of the heads being in perfect shape is unknown as you've already overheated. The conventional wisdom is to send the heads out to a machine shop for grinding/flattening. It's not a full rebuild of the head and most machine shops charge about $50-100 per head for flattening them.

 

You must make 100% sure that your mechanic only uses the Subaru Original Equipment new head gaskets. There are plenty of imitators on the market but the new Subaru ones are almost indestructible. They are a major improvement over the old ones.

 

While the head job is going on, have your mechanic change the timing belt, water pump, tensioner and all the pulleys associated with the timing components. The timing components are likely the original ones and if one of them goes then you lose time and your heads are ruined by the piston crashing into the valve. It would absolutely suck for you to have the heads grinded, new HGs put on but then in a year have one of the timing components go and be back in this position.

 

Another option, however, is this- have your mechanic pull out the engine that is already in there and put in an EJ22 SOHC engine. It is fully compatible with your car. The engine is a SOHC, so if the timing belt or timing components go then you don't lose your heads, you just swap out the bad belt or bad component and reset the time. Also, the head gaskets are way more reliable. You can likely get away with this for around $1200-1500, depending on location. It is something I am in the middle of right now (waiting on the arrival of the engine). Your engine will have a little less pep but you'll get better gas mileage and have a much less complicate engine. I ordered an EJ22 from LKQ for $550. I also bought the LIFETIME parts/labor warranty for an extra $300. I lose engines and transmissions like a hen loses her eggs, so I spend extra on warranties, insurance, etc. The labor warranty covers $50/hr, so not all of it, but if it does go bad you'll be glad you have it.

 

You're in the enviable position of having options to choose from. I am in the unenviable position of having the passenger side cam on my EJ25 freeze up last week at night. It lost time and bent the valve. My car is now sitting in my buddy's garage waiting for the new engine. I am getting around on my bike. Good news- I am getting exercise. Bad news- it's cold in New England.

 

Sorry for the long post. I just took a break from studying and needed to distract myself.

 

Please ask questions. We're here to help.

[MilesFox]

This type of HG failure is due to corrosion of the metal gaskets near a water jacket, where combustion gasses(exhaust) pressurize the cooling system, forcing it out the overflow. then you get bubbles, coolant loss, and then overheat, then head warpage.

 

the 'traditional' way for a hg to go bad is loss of coolant for whatever reason first, then an overheat, then a warpage of the head/gasket.

[1 Lucky Texan]

Bubbles in the overflow tank is an absolute dead give away of a bad HG in a Subaru. Standard HG tests on other cars, is to look for oil/water mixture on the oil dip stick, and do compression test. These tests don't work on a Subaru. I hope your mechanic knows that. If a new head gasket is needed in your future, be sure to use an OEM Subaru HG. Other aftermarket HGs just won't hold up for long.

 

 

Well, bubbles in the radiator to be more specific.

 

A bad/old radiator cap 'could' create bubbling in the o'flow tank.

 

But yeah, the track record here certainly points to HGs.

[spud]

Well, in a last ditch effort to fully confirm the fate of the engine my mechanic did end up checking the thermostat, cooling fans, and pressure tested the cooling system. All those items checked out OK but then those tests may not be reliable (Thanks for the heads up, Rooster2.) In addition, they tested for hydrocarbons in the radiator and overflow tank (Thanks The Dude) and found them in both places in varying concentrations before and after test driving. Bummer.

 

I am currently considering my options: new (used/rebuilt) engine, insert a EJ22 SOHC engine, fix the HG and do any work on the heads, etc., or upgrading to a more recent Subaru. If we go with any sort of rebuilt or new engine I will insist on Subaru Original equipment parts. Luckily we still have my wife's 02 Outback sedan to get around in.

 

Upgrading to newer model has the distinct advantage of more comfortable seats, more and more appropriate cupholders (and other reasons) but it is hard to let go of a car you've known for 13+ years.

[bstone]

Well, in a last ditch effort to fully confirm the fate of the engine my mechanic did end up checking the thermostat, cooling fans, and pressure tested the cooling system. All those items checked out OK but then those tests may not be reliable (Thanks for the heads up, Rooster2.) In addition, they tested for hydrocarbons in the radiator and overflow tank (Thanks The Dude) and found them in both places in varying concentrations before and after test driving. Bummer.

 

I am currently considering my options: new (used/rebuilt) engine, insert a EJ22 SOHC engine, fix the HG and do any work on the heads, etc., or upgrading to a more recent Subaru. If we go with any sort of rebuilt or new engine I will insist on Subaru Original equipment parts. Luckily we still have my wife's 02 Outback sedan to get around in.

 

Upgrading to newer model has the distinct advantage of more comfortable seats, more and more appropriate cupholders (and other reasons) but it is hard to let go of a car you've known for 13+ years.

 

 

Bummer. Sorry. I feel your pain.

[Rooster2]

Well, in a last ditch effort to fully confirm the fate of the engine my mechanic did end up checking the thermostat, cooling fans, and pressure tested the cooling system. All those items checked out OK but then those tests may not be reliable (Thanks for the heads up, Rooster2.) In addition, they tested for hydrocarbons in the radiator and overflow tank (Thanks The Dude) and found them in both places in varying concentrations before and after test driving. Bummer.

 

I am currently considering my options: new (used/rebuilt) engine, insert a EJ22 SOHC engine, fix the HG and do any work on the heads, etc., or upgrading to a more recent Subaru. If we go with any sort of rebuilt or new engine I will insist on Subaru Original equipment parts. Luckily we still have my wife's 02 Outback sedan to get around in.

 

Upgrading to newer model has the distinct advantage of more comfortable seats, more and more appropriate cupholders (and other reasons) but it is hard to let go of a car you've known for 13+ years.

 

Sorry to hear your mechanic's results.

 

About a month ago, I had the same dilemma with my 98 OBW, with the exception, that I knew my motor was cooked, and could not be repaired. Exact replacement used 2.5 motors are difficult to find and expensive, and carry the inherent risk of blowing HGs again. I thought about upgrading to a newer car, but my money is tight, and the 98 OBW is still in good shape, so I elected to have a shop install a 1995 2.2 motor. Overall cost came to about $2,000, but figured I couldn't buy much of a car for $2,000. The result is I got a good running 2.2, that is non interference, not prone to blowing head gaskets, and much easier to change spark plugs. The 2.2 lacks 30 horsepower compared to the 2.5, and yea, I can feel the ponies are missing. However, it is not that much slower. I am glad that I have gone the 2.2 route. Just my 2 cents worth of testimonial for what that is worth.

[the3rsss]

Everything I have read on this forum and others is that the 2.5 is a good engine with bad head gaskets. Also that the oem replacement gaskets are well made and will last. Rooster, why do you say ......"inherent risk of further head gaskets failure" with regards to the 2.5?

[Rooster2]

Everything I have read on this forum and others is that the 2.5 is a good engine with bad head gaskets. Also that the oem replacement gaskets are well made and will last. Rooster, why do you say ......"inherent risk of further head gaskets failure" with regards to the 2.5?

 

Yea, the 2.5 is a great engine, plenty of power, but just plain snake bit with initial poor HGs coming out of the factory. I went over board on saying "inherent risk," I should not have come on that strong. So............okay, let's hear some testimonials from owners with the latest and greatest HGs on their repaired 2.5 motors, saying that they have driven 50K+ miles with no HG trouble, and are confident that their HG problems are behind them.

[Mike104]

Yea, the 2.5 is a great engine, plenty of power, but just plain snake bit with initial poor HGs coming out of the factory. I went over board on saying "inherent risk," I should not have come on that strong. So............okay, let's hear some testimonials from owners with the latest and greatest HGs on their repaired 2.5 motors, saying that they have driven 50K+ miles with no HG trouble, and are confident that their HG problems are behind them.

 

I think the longevity of a 2.5 that has had the HGs replaced depends a lot on the care taken to do the job. Some dealers do the job in the car and may not get a good cleaning done. Some don't check the heads for flatness. Most DIYers remove the engine to do a good job (like this guy)

 

Good cleaning and prep work combined with latest Subaru gasket seems to have the best potential for long life. Those that remove the engine and do the "while you are in there" stuff also seem to have fewer problems.

 

The SOHC engines are a bit easier to do in the car, but some still prefer to remove the engine and do everything with the engine on a stand. Just my $0.02

[nipper]

+1

 

HG jobs come down to two things, one is a very good replacement part, the other is surface prep (flatness and cleanlyness). Gaskets only really seal on the edges, so any high point makes a new edge and the immediatly surrounding areas has less sealing force and allows for a path.

[the3rsss]

I have replaced headgaskets on a dohc 2.5. I am just amazed anyone would even attempt this job on the car. With that said.....is there any reason to believe that with updated gaskets, properly cleaned and torque etc, that the 2.5 won't last as long as any other subaru engine?

[nipper]

It will last just as long, as long as oil changes are performed regularly, coolant changed regularly, as well as timing belts.

 

 

The 2.5 DOHC was built to the max that the engine materials (at that time) could put out. There was an excellant article quoting Subaru's President that the 2.5 was built to the very edge of all the power they could get out of that engine. This is why the 2.2 is so robust, there is plenty of room to build upon.

 

Also remember that not all 2.5's have this issue, and quite a few are piling on the miles.