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friendly_jacek

Another scenario for the HG failure

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This was a very interesting thread that didn't get a lot of attention:

http://www.ultimatesubaru.org/forum/showthread.php?t=55545&page=2

 

The last 2 posts are what want to bring again for discussion:

 

"Quote:

Originally Posted by broke subaru

Thanks. I said I would keep everyone updated so here it is. I went to see my mechanic today, he had the left head off and it did have a blown gasket. He said when he took the timing belt off it was loose and he could spin the water pump by hand. He thinks the belt tensioner was not keeping the belt tight enough and the water pump was not being turned. This caused overheating and the gasket failed. He did not think the gasket was inherently bad. On a good note, he showed me the cylinders and they still had crosshatch hone marks. At 140,000 miles thats pretty impressive.

 

I am starting to believe that, in my case, the problem was not the gasket but the engine cooling system. The original belt tensioner probably wore to point that the belt was not tight enough to consistenly turn the water pump. My first mechanic replaced the tensioner 4 times because each one he was sent did not have adequate tension. I am trying to locate an aftermaket/ high performance tensioner to prevent another overheating problem.

 

 

I think you hit the nail here. We blame the HG problems on weak gaskets and open deck engine design, but the problem may also be the consequence of overheating not cought in time by the driver. It has been shown by the airplane engine experiments that that improper coolant change with air bubbles in the cooling system can overheat the engine and blow the gasket.

Now, we have another scenario with bad belt tensioner. I can atest that the subaru tensioners are POS as I replaced one twice under warranty in 60000 miles!

One interesting thing is that the bad tensioner sounds like engine knock or piston slap but with one salient difference, it comes from belt cover area.

I would urge anyone with "piston slap" to invest in stethoscope."

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ive been beating the drums saying that overheating can cause a HG failure, as well as a HG causing over heating. also been stressing that regular antifreeze changes are just as important.

i just never thought of a slipping belt against the waterpump as being the catalyst for destruction. Learn something new everyday.

 

nipper

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What is it that you would like to discuss?

 

Are you looking for a new explantion for head gasket failure?

 

I think he's trying to drag this concept (of overheating causing headgasket failure) out in the open a bit more. I've noticed a tendency to simply reply "Headgasket blown" when somebody says their Subie is overheating and has the symptoms of a blown HG.

 

Heck, the used car dealer that I bought my '97 OBW did the same thing. He bought it from auction, discovered it overheated consistently and had all the symptoms of a blown headgasket. So he swapped the headgasket, water pump, etc. Everything except the radiator, which was clogged as all heck - http://www.ultimatesubaru.org/forum/showthread.php?t=51689.

 

So this guy went through two EJ25 engines (finally swapping in a 2.2 at my request), simply 'cause he was too obstinate to pull the radiator (I asked him repeatedly, he glazed over it, saying he "checked it out". My arse he did. I won't be bringing anything back to him).

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I am very aware that overheating an engine can lead to head gasket failure, generaly speeking.

 

When talking spacificly about Subaru engine head gasket problems there seems to be a lot of misunderstanding of the cause and effect between the different engines. Subaru head gasket failures don't present the same simptoms as the average car and a lot of the time are misdiagnosed. Parts are replaced overheating problem continues, then there is a question of weather the head gaskets caused the overheating or the overheating caused the head gasket problem.

 

This post is refuring to the SOHC 2.5L engine. Totally different problem than the DOHC 2.5L as far as the head gasket issue is concerned. Normally the SOHC head gasket problem dose not cause overheating. It is an external leak and will only cause overheating if it leaks enough for the cooling system to become low on coolant. In which case the cause of overheating is low coolant. If the leak is not fixed and the engine is continuly over heated it could lead to head gasket failure.

 

In the post that is refured to hear there are just a lot of variables, age and condition of timing belt and water pump to start with. I've seen quite a few weak timing belt tensioners but never overheating problems related to them.

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I like the premise of the assertion, but as a logical droid, I must play the devil's advocate.

 

The tensioner has two active components:

 

1. Spring tension.

2. Hydraulic damping.

 

A bad batch of tensioners found their way onto a limited number of EJ-25's resulting in a TSB. The problem was lack of hydraulic damping which allowed the tensioner to bounce. This differs from the assertion that the tensioner lacks adequate spring tension by design.

 

I ask; if the tensioner in general has a lack of tension by design, then why are the EJ-22's not having the same gasket problem?

 

**** ******!

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So did you replace the radiator when the 2.2L was installed?
You betcha. After the 2.2L swap, we drove it home, without it acting up (of course). Took it for a really short drive the next day, the temp. gauge started to rise just as I pulled into the parking lot in front of the apartment. I pulled the radiator a few days later, tipped it upside down, and a load of mineral deposits fell out. Not good. I swapped the radiator soon after that, and I haven't had a problem since.

 

I'd wonder about the tensioner bit, too. We just had the one replaced on my wife's 2000 OBW while it was in for the warranty work (getting that driver's side headgasket replaced - external leak). I had originally misdiagnosed it as pistion slap, since it would sound like "a dozen walnuts simultaneously and constantly being bounced off a thin wooden board". After warming up the engine, the sound would disappear. Dealer caught it, replaced the tensioner (for a charge, obviously), and the noise disappeared. Apparently the tensioner was failing to take up the slack in the belt when cold, allowing the belt to slap, causing the noise. Allowing the engine to warm up also allowed the oil in the tensioner to warm up, presumably allowing the tensioner to start functioning properly and put tension on the belt, preventing/reducing the slap.

 

Going from that experience, if the timing belt was that loose (since the tensioner wasn't functioning), you'd be able to hear something along the same lines (since the belt should be slapping around a bit). Especially if it's so loose that it won't turn the water pump. That's just my two cents, though, and the standard disclaimer applies.

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The vehicle referred to here is mine. One of the reasons I think a loose timing belt might be my problem is that the overheating is intermitent. My first mech. replaced the radiator,water pump, thermostat, belt, belt idlers and the belt tensioner. He had to reorder the tensioner 4 times because the first 3 had almost no tension in them. The old belt had a lot of scuff marks on the back of it and he thought it might be slipping on the WP. I took the car to a Subaru dealer because of continued overheating. It did not overheat for them, but did on the way home. They finally diagnosed the blown HG.

 

If the HG caused the overheating why does the OH come and go? Also what caused the first OH ? The radiator was bad (half clogged, probably from the stop leak Subaru put in it) if that caused the first problem why did a new one not fix it? I don't know the answers to these questions and, so far, no one I have taken the car to knows either. I really want to prevent this from happening again whatever the cause.

 

PS: If the belt can bounce due to lack of tension/dampenin/cold fluid or whatever, could it not be skipping on the water pump, causing poor flow?

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Bottom line is the EJ-25 is loaded with bad kharma. A veritable witches-brew of bad design & poor judgement all rolled up into one really swell ball o' crap. :rolleyes: :-\ :rolleyes: :-\ It forced me to buy a second car (yes an EJ-22).

 

I've had bubbles and black flakes in my overflow for the better part of two years. It hasn't gotten better or worse in that time.

 

**** ******!

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The head gasket/overheating thing is a chicken or the egg situation. Head gasket failure causes overheating, and overheating causes head gasket failure, but which came first in any particular engine may be difficult to prove conclusively. My guess is that most EJ25's start to leak just a little bit of exhaust gas into the coolant, which eventually causes overheating, which then leads to a much more severe head gasket failure.

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My guess is that most EJ25's start to leak just a little bit of exhaust gas into the coolant, which eventually causes overheating, which then leads to a much more severe head gasket failure.

 

This is true for the EJ25 DOHC engine mostly 97-99. The 96 DOHC had different head gaskets and not as many were made, so the problems with them aren't as prevalent. I have done head gaskets on 17 of these engine (since I've started tracking parts usage), and have replaced at least 3 engines because they were driven hot untill the engine seized. Symtoms are always the same and the gaskets all leak in the same place. They all overheat instantaiously without warning, there is always sings of hydrocarbons in the cooling system. This problem can be intermitent in that the gaskets won't leak enough to cause the engine to over heat untill fully warmed up and put under load. They can idle all day, or be driven around town all day and not overheat. Due to the nature of this problem it can be difficult to diagnose. So there are a lot of thermostats, water pumps, and radiators being replaced to fix the problem, but the problem continues, then all that is left is the head gaskets, and the question of what was really causing the overheating. And once a shop has sold someone all these other parts you can bet that they are going to tell the customer that those parts were needed and the overheating caused the head gasket failure. Once you become familure with the cause and effect, the overheating problem with these engines is no mistery, and easily diagnosed. Also, I've said it time and time again, Subaru did not stop production of this engine after 4 years because it was a good design.

 

Now I'm not saying that a restricted radiator can't be the cause of over heating problems that could lead to head gasket failure. But in my experieance that has never been the case and I have never had a come back for overheating after completing a head gasket job.

 

Now on to the EJ25 SOHC engine......................................Same blood line different animal. I don't have as much first hand experiance with this engine due to a lot of them still being under the origianl warranty or the stop leak extended warranty. But that is starting to change. This engine has a different head gasket issue. The head gaskets are leaking antifreeze externaly (never a problem with the DOHC). If this leak is bad enough the engine can over heat due to low coolant level (been there done that, fix one). Could this cause a head gasket failure that could lead to more over heating? Yes theroreticly it could. The 2000 and newer OB radiators have a tendency to leak at the seam between the end caps and core, leading to low coolant levels that could lead to over heating, that could lead to......................................

I have diagnosed one of these engines as having blown head gaskets that were causing an over heating problem. It was easaly diagnosed and had all the conventinal signs of blowen head gaskets that you would expect to see on the run of the mill automobile. Coolant was leaking into the cylinders (never a problem on the DOHC). This was after another independent repair shop supposedly was paid to repair the external head gasket leak under warranty. I didn't have the pleasure to pull the heads on this engine and see what was going on because the Subaru dealership was supposedly going to repair the car this time, again under warranty. So I can't say what is most likely to cause over heating problems with the SOHC EJ25.

 

The moral of my story is that I don't think you can group all the EJ25 SOHC and DOHC engines in the same category. What someone thinks went wrong with one SOHC 2.5 isn't going to explain away the head gasket problem of the DOHC 2.5. The loose timing belt not turning the water pump may be a good therory, but would need to be proved. The car in question was never properly diagnosed the first time around and continued to over heat, which in turn can coutinue to cause more wear and more problems and by the time you get every thing fixed and stop the over heating problem it's a little hard to put a fingure on the root cause.

 

I will stick to the facts of more than 20 hands on cases that I have had with the DOHC engines, and do my best to properly diagnose any over heating problems with the SOHC engines to determine if there is a pattern failure with them also.

 

Then some day I may write a book:rolleyes:

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I should have been more clear, I was speaking of Phase I EJ25's only.

 

I kind of ASSumed from your screen name and other threads that your experiance was with the DOHC. But I question weather others who are looking for an explanation to their particular problem are going to know that.

 

The reason for this question was to try to determine which HG failure was to be disscued in this thread. I too should have been more specific.

What is it that you would like to discuss?

Are you looking for a new explantion for head gasket failure?

 

The title of the thread is "Another scenario for the HG failure". And refured to a post about a SOHC engine.

 

I was trying to determine weather he wanted to talk about the SOHC HG's or the DOHC HG's. Two different discussions, but inevitably the title is going to lead to discussion of both problems.

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