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Subaru head replacement--cheap gasoline the culpit?

I am forced to replace one of the heads on my Subaru Legacy turbo charged engine at nearly 80,000 miles. Valve problems. Service manager said that cheap gas can be a cause of this problem along with extended oil change intervals. He recommended only top tier gas brands–and thought buying at COSTCO was a possible cause. I had changed oil every 5000 miles with Mobil 1, even though the recommended change interval is 3750-- but car driven mostly on highway, never start and stop.

Do you think gasoline might be the villain? Should I stop buying at Costco and use only top tier brands?

Thanks for your advice–the thousands of $ in repair costs makes my saving .10-.20 a gallon a foolish choice

Rather than brand of gas, this could be the result of the wrong grade of gas.
This car requires high-test/premium gas, and if you were using anything of lesser octane, damage to various engine parts can be the result.

In what kind of shape are the valves?
Have you consistently used high-test/premium gas?

always premium fuel without exception

What exactly is wrong with the head that necessitates replacement?

I personally believe some brands of gasoline are of higher quality than others, others will disagree and I won’t argue. But certainly if the car does specify a certain level of octane, that’s important. A friend who runs a Shell station (and I don’t buy his gas very often as his prices are too high) says his fuel is sampled regularly to be sure the octane is as specified. He also mentioned Chevron as another that is more consistently checked. I’m also OCD about oil and wouldn’t go much beyond the recommended interval, even with highway miles, but that’s me.

I was not aware that a select group of companies are designated TOP TIER , you can do a google search to find the list. The Service adviser recommended using those brands–but he had to have some answer, and oil change interval did not seem probable

The Top Tier brands of gas (Shell, Exxon, and Chevron are 3 that come to mind) have a higher level of detergents than the EPA requires. That could be very helpful with keeping your fuel injectors and intake valves clean–particularly if you have one of the new direct-injection engines. However, I am unsure about how a higher level of detergents would have prevented this problem with the cylinder heads.

What exactly is the problem with the valves and the heads?

Remove the Owner’s manual, likely in the glove box, and check what octane your engine needs. I believe it it will require mid or high octane. The owner’s manual likely will say it should have or requires a certain minim octane.

Not using the prescribed octane can cause damage to your car and reduced power output.  If it only "recommends"  the high octane, you can use regular, but you will get lower mileage and power.

By simply entering the word “Subaru” into this boards search feature, you will find the thousands of other somewhat less than happy Subaru owners who detail their sad laments on this forum…When you take a rather fragile engine and force-feed it, 80,000 trouble-free miles seems reasonable to me…Subaru mechanics enjoy full employment and are not going to blame their employer for building less than perfect cars and engines when they can lay the blame on “cheap gas”…If “cheap gas” was the problem, it would have manifested itself much sooner than 80,000 miles…This is just junk wearing out…

I wonder if a coolant change could help head gasket life. I have dumped dexcool, Dno’t know what’s in a Subaru, and wonder if you think it might be relevant, or are the gaskets just prone to failure?

First off, you will probably save money by replacing both heads as long as you’re getting into a tear down. Your valve problems are likely replicated in the other head.

More importantly, oil change intervals are particularly critical with turbocharged engines. Turbos (the turbocharger unit itself) have really tight clearances and are subjected to high heat.

The oil change interval deficiency would normally show up in friction surfaces (bearings)inside the turbo and elsewhere not valves. Since you’ve exceeded the interval regularly for 80K miles, I’d place the blame there, with too infrequent oil changes, not the gasoline grade you’ve been using

While you’re at it, get the timing belt, water pump, tensioner changed while you’re in there. It’s early but I think you’ll save some labor charges.

Cylinder head valves and pistons can be damaged by the use of gasoline that does not have enough octane required for that particular application. It’s not a matter of gasoline quality; it’s about the octane rating and possibly some contributing factors.

If the EGR system is not working correctly this can be damaging to the valves/pistons and a problem there could be the real reason behind this. In other words, if the EGR system was fine then this problem may not have occurred.

What I have an issue with is the word head being used in the singular if this is the case. If one is bad enough to require replacement then why are they leaving the other head alone? It’s not like one side is trashed and the other is fine.

Since we do not know exactly how the dealer arrived at their conclusion, some food for thought could be that the entire valve issue is caused by incorrect valve lash and has nothing at all to do with gasoline quality or octane rating at all.
That could explain one head “bad” and the other fine.

might be this and might be that? What exactly is wrong with the cylinder head? What was the failure mode? He cannot in any scientific way say your oil change interval caused the issue. I am a 30 ASE master tech and work for a large oil filter company. There is now way this should have happened unless you have been using 87 octane gas and you have detonation damage. Interested in hearing the rest of the story

Based on your driving pattern and changing oil at 5000 miles as well as using high quality oil, it’s very unlikely that your oil or change interval had anything to do with it. If you consistently used high test gas, that is also a very unlikely cause.

As others point out, the problem could be cooling system related.

The service manager is GUESSING! He is right that too long an oil change interval can cause problems, but that would have to be 10,000 miles or so of city driving. In all cases he wants to divert the cause to something YOU did instead of an inherent problem with that type of engine.

Costco gas is fine as long as you tank the right grade for your car. Costco’ policy is to only sell good brands, that’s why they are so successful.

Service managers are hired for their administrative and sales ability, not for their technical expertise!

This is actually a rarer failure for the 05-09 2.5 Subaru turbo. The typical failure of the motor is the turbo in 2005-early 2006 due to a turbo line filter that clogs. In doing so the turbo falls apart and introduces metal to the short block ruining it.

I am unclear on what valve problems entails. However gasoline has little to do with it.

I own the same vehicle 2005 LGT and use premium but any brand. I have had no issues over 106,000 miles.

Not sure why the Subaru 2.5L engine (turbo and non-turbo) is so troublesome in Outback/Legacy. In the WRX/STI its very reliable. There past engines were very reliable including 2.0L turbo(WRX), 2.2L, 2.2L turbo and 1.8L. Not sure where Subaru lost their way.

The force fed motors by Subaru are typically more reliable than the non-turbo counterparts. It is not the same motor.

WRX and STI owners with high sprung turbo motors enjoy incredible amounts of power under boost with decent longevity/reliability. Not sure if this is the difference but those motors/cars are built in Japan not USA.

Since you stated you use premium grade all the time I really don’t think this problem has any relation to the gas you bought at Costco or anywhere else.

I think your turbo could be set up be a problem. There is a waste gate somewhere in the system to limit the boost pressure. To much boost or too little can cause problems. A knock sensor should handle pre-ignition but perhaps can be overwhelmed if boost pressure is out of range.

I’m not sure it is the turbo, but it ain’t the gas. Subaru’s are prone to head problems. They also can run hot and are prone to overheating. Not sure what the root of your problem is, but the cheap gas is a BS excuse.

Subaru’s are prone to head problems.

True for non turbo 2.5L engines. However it is quite rare for a turbo Subaru to have head problems

Does this engine have solid lifters?
Some car makers are in denial about valve lash adjustment.

Stopped by dealer, he said issue was a valve guide that dropped, creating a check engine light and low pressure when the did a leakdown test. I think both the oil change interval and cheap gas are bogus causes–but not sure if there is anything I could have done