Overheating & Head Gasket (confirmed head gasket)

[MH3.0R]

Hi all,

Having some recent issues with an occassional over temp problem. After casual cruising at highway speeds followed by stop/start city driving, I find the temp gauge occassionally almost in the red zone. It happens very quickly and then after driving again at 60 kph all things come back to normal. Day can be hot as (40 degs) or raining (18 degs) makes almost no difference.

Took the car into STI@Docklands and they ran it on a dyno under load, found some air pockets in the cooling system, bled them out and then all seemed ok. Within a week, I noticed it starting to happen again on a mild wet day (last Friday in Melbourne).

Back to STI again today and they did manage to see the same symptoms I described (that it happens quickly, then goes away). The mechanics indicated they should just change the thermostat and flush the radiator, but the technical guru at STI (Steve) discarded that solution because of the characteristics underwhich the over temp occurs.

I tend to agree with him. If the thermostat was crook, then I should see longer lasting over temperature situations. If it was a radiator blockage, then similarly, the over temp would not be fast and intermittent.

STI indicated it would most likely be a head gasket Hard to say precisely which bank, but given that the 3.0R utilises a metal head gasket, a crack between exhaust and compression chamber may expand enough to open up after some high thermal load and then close up again after the vehicle get back in motion with the more efficent cooling.

So, not being a mechanical engineer (other than many weekends spent with my dad in my formative years pulling down engines and gearboxes and helping with re-builds), I am open to suggestions or experiences pertaining to the sources of overheating on the 3.0R.

Also, any recommendations for head work if they do need to come off. STI maybe on the expensive side and I know there are some good specialists in Melbourne, just not sure if they have experience with the 3.0R.

Mark.

[BlackFlatSix05]

Mark,

Just curious, how many k's on your car ? Do you tow with it ?

[Ric]

No milkiness showing in your oil?

The ECUDatascan would give you a much earlier indication of when temperature rise is occuring. The stock needle sticks dead centre for quite a wide temperature swing...

[MH3.0R]

No "milky" oil. Still as good as new from 15000k ago. Good stuff the Redline. Combined with the Trasco high particle filter.

I checked all the obviousoil in water and water in oil, plus STI did a compression test, but when the engine is just idling from a cool start or warm start, all is ok.

I first diagnosed the problem while using the ECUdatascan. Spotted it very early and saw the high rate of temp rise first time back in Nov 09. Then again on our Reefton run, after lunch just when I hit trffic lights after Lilydale on the home run. But because it is intermittent, it was frustrating to explain to the guys at STI. Then when STI took it for a drive themselves and spotted it also, they were convinced that the issue is not related to the usual candidates.

So, do I let them take the heads off to catch the problem as early as possible? Or should I wait until the problem is consistent? To my way of thinking, best to have the heads off, machined, new gaskets, flush radiator, new hoses/clamps and new theromstat while they are at it. They are going to have for about 3 weeks! Sounds a bit too long for me. Maybe their focus is regular maintenance and not so much in the refurbish/rebuild area. That is why I am looking for specialists in the Subaru/Head area.

[MH3.0R]

Mark,

Just curious, how many k's on your car ? Do you tow with it ?

No towing, but do have a tow pack as the auto gets the transmission cooler as part of the tow pack. Bloody expensive transmission cooler though!

Car has 169,000 approx. So I am considering that it maybe time to do a large and comprehensive service. Timing Chains, Belts, Hoses while the car is off the road for a few weeks.

[Ric]

Have you ever used the ECUdatascan in logging mode?
You can make some nice timeline graphs in EXCEL with just a few button clicks.
A graph showing water temp, air temp, speed, revs and engine load over a decent drive may be useful.

[MH3.0R]

Yeah Ric, I will try that as the over temp occurred again this evening after the drive home from work (steady cruise on the Monash). It happened in the last minute after pulling off the highway and into the 50 zone of the estate. Within two minutes, not more and just idling while waiting for the garage door to raise. Not over temp in the red zone, just about 2/3rds of the scale and the fan came on.

So, yes, I will do some extensive logging to aid in the diagnosis.

[MH3.0R]

Well, got my quote from STI and they want 4.5 grand for the head job! Plus the flush, thermostat, oil filter, oils, etc. It will be the most expensive head job I have ever paid for!

Come on with your suggestions and recommendations.

I have already launched one with a local repairer, Peerless Automotive. They say they have an ex-Subaru mechanic working for them, so I will see what they quote and ask questions to see how knowledgable they are on the H6.

[smythie]

So, to summarise:
- it only happens after a bit of operation.
- temperature is fine when cruising down the highway
- sometimes after a period of running (eg: highway, run through the spurs) when you pull up the temperature goes through the roof.
- start moving again and the temperature returns to somewhere near normal.
- has so far only been happening in the heat of summer (I wonder if it has been sitting hidden over winter)

I experienced this sort of behaviour on the bike (Triumph). IMO that thing had an undersized cooling system.

In your case, I think the fan control/power could be part of the problem. It would be an intermittent fault whatever that happens to be:
- Maybe a fan that runs sometimes but not others when commanded to run;
- Maybe a dodgy wire or connection in the power for the fan;
- Maybe a dodgy wire or connection between the thermostat and the fan power relay (I'm assuming here that the thermostat closes/opens a relay, contacts on which are in the power circuit for the fans)
- Maybe a dodgy thermostat

If you aren't seeing oil in the water or water in the oil, the only other leak from a head gasket that will affect the cooling system will likely be evident in the form of bubbles in the radiator water. You may also see a large amount of coolant being forced out of the radiator into the expansion tank when the temperature sky rockets

Good compression test results indicate to me that there isn't a problem with the head gasket (or the rest of the combustion chamber sealing for that matter). I wouldn't read too much into a possible difference between hot and cold personally. Any crack in a gasket that *might* widen with heat will cause compression to drop when cold.

I'd be checking the fans, their power and their control before pulling heads off for a suspected head gasket. Particularly if the compression test was good

JMO

Disclaimer: I may be a mechanical engineer by education but I'm not an experienced motor mechanic

[MH3.0R]

Hey, thanks Smythie,

I was wondering if there were others that held a different opinion and precisely the sort of feedback I was looking for.

I was reading through the Service Manual and they have a lot of diagnotic tests that can be performed on individual elements, but they require removal. I was a little surprised/dissappointed that STI did not perform a comprehensive test of all elements of the cooling system. They seemed to be leaning heavily on the head gasket potential problem.

To have the car off the road for 3-4 weeks for a "potential" problem is very disconcerting for me.
On the brighter side, at least I would know if there is a head problem!
But then, the cost of finding out is pretty steep!

[WhiteGTB]

Very interesting topic.... keeping an eye on this thread.

[Viper]

Some ideas;

Might have missed it, but have you had your system pressure checked?
Most decent radiator places can do a pressure test on your cooling system.
Even if its 'heat' related might still show something.

Are you actually loosing coolant?

For the sake of $5 have you replaced the thermostat?

Also, as the post above suggested, check to see if your thermo fans are actually running.
i.e. when the heat skyrockets, just pull over and take a look.

Finally, considered that the temp sensor could be faulty or the wiring is dodgy?

[MH3.0R]

Viper,

Thanks for the suggestions.

Have done a pressure test and compresion test, both good.

Am leaning toward a sticking thermostat and/or poor fans startup (including the dodgy wiring and connections).

Fans do start ok, but not until temp is at ~104 degrees C (according to the ECUDatascan). I noticed this usually as I pull into the garage at either work or home.

Did some logging on the way home this evening and saw a spike after a 15 minute 100 kph run slowed to stop start. The spike was a quick rise to 104 degrees C. Once traffic picked up again above 50 kph, temp start to come back down to normal 91-94 degrees C. Interestingly after a further 15 minutes at 110 kph, and entered an extended stop/start section for 30 minutes more, there was no sign of over temp. Remained consistently around 94 degrees C.

I am starting to think there maybe a sticking thermostat or a problem with water or air flow (pump or air lock). You might be on the money!

[MH3.0R]

Just been reading the Service Manual again, and they indicate the Fans should come on Low at 95 degrees and transition to High at 100 degrees. I think I may have stumbled across the potential problem as I am sure I heard no Fans until 104 degrees. Ok, so now I have some specific tests that I can focus on this weekend in my own garage while logging with the ECUDatascan. Hope it is a Fans problem. It should be a lot cheaper than 4.5 grand and no loss of vehicle for 3-4 weeks and no heads removed!

[smythie]

so do I.