2006 OB coolant bubbling, overheating, combustion gasses not present

[Pauldoug]

I own a 2006 Subaru Outback wagon 3.0 liter R, 130k miles. Car is randomly overheating (not red-lining, but almost). Sometimes you can drive all day, no problem. Other times, temp needle creeps up to near the red. Several months ago (before the problem started), the radiator hose burst (car was turned off before overheating). So, shop put in new hoses, belts and coolant. Recently, this problem started, so I drained the coolant (was very clean), flushed the system with plain water, including the hater core. Installed new Subaru thermostat. Filled 50/50 with Subaru Long Life coolant, and Subaru Coolant Conditioner. Burped the system per instructions. Also replaced the radiator cap with a new Subaru cap. Problem continued.

 

There are no obvious leaks that I can see.

 

Typically, needle will be steady in the middle, but will suddenly start climbing after a lot of driving, then go back to middle. I think both fans are running, even with the A/C off (expected if engine is hot). Advice I've been getting is that this is a HG leak, especially because often the overflow tank will boil -even if the car car hasn't overheated.

 

 

Here's an update, after a few weeks. Now I'm more puzzled than ever! First, a little more info. The car never gets above-normal hot at highway speeds, even if I've been driving for a few hours. It can start when I get onto local traffic AFTER having been driven fast. (Note that I'be never allowed the needle to go although way to red). The usual behavior is that the the needle will slowly go up and then back down to the middle position. Later, if I'm back on the highway, it goes back to its normal position a touch below middle, and stays there. If I pull over and look under the hood, the overflow tank is full and boiling.

 

After these incidents, I always top off the coolant. (The boiling causes coolant to spill out of the overflow).

 

I know many of you are thinking that this is definitely a head gasket failure, like I've already been told. Well, stay with me because this gets interesting.

 

Recently, I took the car out and was in local traffic for approximately a half an hour. I was on a highway for about 5 to 6 minutes during this drive and reached a speed of 50-60 miles an hour. When I arrived home, I opened the hood and saw that the overflow tank was bubbling. (Note that the car was not overheating at all during this drive). But I was glad to see the bubbling, because I could now do a test. I am in possession of a block tester kit that I had been loaned from AutoZone. This is one of those gadgets that allows you to suck air into a clear cylinder into an indicator liquid. If the liquid turns yellow, you know that there are combustion gases present. I stuck the device into the overflow tank (not the radiator itself, of course, because the engine at this point was hot). The coolant in the overflow tank at this point was 4 to 5 inches below the level of the device, so there was no chance of sucking any coolant into the device. Bubbles were still coming out of the the overflow tank tube. Following the directions, I squeezed the tube for two minutes, probably more like three. And … (wait for it) …

 

Nothing. Nada. The liquid did not change color at all. It stayed the same shade of light blue the whole time. This should indicate that NO combustion gases were present coming in the overflow tank.

 

Now, the cynical among us may say "well, how do you know that that indicator liquid even works? Maybe it's just water with blue food coloring." Well, I thought of that. I did something else as a control. I walked to the back of the car, while it was still idling, and put the block test device near the tailpipe and squeezed the bulb in and out a number of times. Within seconds, the liquid changed from blue to yellow. This indicates to me that the block tester is working.

 

I've done this test several times since, sometimes on the overflow tank, sometimes on the radiator. Same result.

 

Oh, and one more thing: often the bubbling continues for about a minute or two AFTER the ignition is turned off. How could combustion gasses be bubbling out of the overflow tank if the car's not running?

 

Also, I pressure tested the radiator with the engine off. The needle hardly moved in 10 minutes.

 

The fans are running if I check under the hood after pulling into my driveway.

 

So, (considering all this info, sorry) do you think I'm right that the issue here is not a blown head gasket? Is air getting into the cooling system, or is air trapped in the cooling system, or is a leak causing the coolant to boil (because the system loses pressure)? Should I get the coolant system refilled professionally (under vacuum)? What's the next step?

[1 Lucky Texan]

when the car is cool after one of these events, is a radiator hose ever collapsed? Does fluid get pulled back into the radiator from the overflow tank?

 

another way to think of that question - after the car has cooled, AND there is still coolant ion the overflow tank - even a coupla inches - is the level in the radiator up into the neck? Ever any 'whoosh' of air when removing the rad cap?

 

have you looked for buildup of dead bugs/debris in the radiator fins?

 

Any transmission shifting problems? have you check the trans fluid level? (must be checked while idling)?

 

Have you tried turning on the heater full blast during an overheat event? what was the result?

Edited August 1, 2016 by 1 Lucky Texan

[DaveT]

Pressure test of coolant system won't show up the pinhole headgasket failure. The psi in the cylinder is many times higher than the coolant system pressure. The gas tester thing I have heard many reports that it often does not detect for some reason. The bubbles continueing for a bit after shutdown is no surprise. The pressure takes time to build up, and time to bleed down.

[Pauldoug]

1 Lucky Texan, thanks. Here are the answers to your questions:

 

Coolant usually (but not always) gets sucked back into the radiator, especially if the car sits till I the engine is stone cold. The hoses are not collapsed. Usually the level in the radiator is up to the cap, but not if coolant had been pushed out of the overflow.

 

The transmission was checked recently (professional mechanic), some fluid added. No shifting problems.

 

Radiator is clear of debris.

 

I always turn the heater on if the needle heads north. It helps some, I guess, but not as much as driving faster.

[steve56]

Bring your car to shop that has an electronic HC gas tester. Car needs to be hot with bubbles in the overflow tank. Most importantly, you need to watch technition do the HC gas test. If the HC testers numbers increase you defindately have HCs in your cooling system.

[mikaleda]

Well air is getting into your system somewhere. If for a fact you do have the system burped properly (which it sounds like you do) and there is no leaks in your cooling system, the only other way for air to make it into the system would be headgaskets how ever unlikely that sounds.

The block tester kits can be unreliable on Subaru's for whatever reason, so I wouldn't rule the head gaskets out just because its not detecting a leak.

[Pauldoug]

Dave T, thanks for your reply.

 

Good point that the pressure test on the radiator wouldn't show an internal leak in the engine. I did the test to rule out (I hoped) that there could be a leak the in a hose, heater core, etc.

 

You're not the first person to suggest that the block tester might not be sensitive enough to always detect combustion gas being present. After all, the sniffers that garages use for emissions testing are way more sensitive. But, in my test, the coolant was really bubbling, not just "bloop, bloop". So a significant portion of the gasses present (other than some air already in the tank) would be water vapor (from the boiling coolant) and (only if the head gasket is leaking) combustion gasses, right? That would trigger a change in the fluid color, no? Let me be clear: the fluid stays the exact same shade of blue the whole time.

 

Now, maybe I don't understand the mechanism of what could be happening. Does even a tiny HG leak cause the coolant to boil, even though the amount of combustion gas present could be a very small percentage of the total gasses present?

 

You may be wondering, why don't I just get my mechanic to get out his sniffer? Only because if they idle the car for awhile to do the test, they might not find anything. I'd have to drive my car around for while, and then drive up to the place, horn beeping, and yell, " Quick! Get out the sniffer!" I'm only slightly exaggerating. But I'll probably do that soon. Btw, I've heard that tests on the cylinders (compression, leak down) could be inconclusive. Everything is sealed when the the car is cold.

 

Also, what does anyone think of the possibility that there's air trapped in the system (even though I've burped a number of times). Also, I've thought about the water pump, but I don't see leaking out of the weep hole.

[Pauldoug]

Thanks, mikaleda.

 

Everyone is pointing to what I should be doing: stop fooling around, and get the thing professionally tested for HC's. I'll do so in the next few days, and post the result.

[1 Lucky Texan]

Are you second owner? Is it your feeling the car has always done this since you acquired it? (kinda wondering if prev. owner(s) could have run straight water and water pump vanes are eroded-away - hey, anyone?, can the WP impeller be viewed thru the t'stat hole?)  http://www.subaruoutback.org/forums/66-problems-maintenance/45334-here-s-new-one-trashed-water-pump-vanes.html

 

I wonder if Blackstone or Polaris or similar labs could test a fluid sample from your radiator for combustion products - might even be more affordable than 1 hour minimum at a mechanic's shop.

 

kinda wonder what comparing all 6 spark plugs to each might show.

Edited August 1, 2016 by 1 Lucky Texan

[DaveT]

With that steady of a stream of bubbles, you don't have long before it will be undriveable. My experience is mostly with ea82 and older engines.

 

Here is the short version. Un noticed leak causes low coolant. Engine runs hotter than normal once, while low on coolant. Replace coolant. Notice slow bubbles. Days, weeks or months later, progresses to fast bubbles. Every overheat while low on coolant accelerates the demise.

[DaveT]

Bye overheat above, I mean over normal temp, not nesisariy in the red.

[Pauldoug]

1 Lucky Texan:

 

I am technically the 2nd owner, but I bought the car from a Subaru dealer with about 7,000 miles on it. Hmm… I might be able to get eyes on the impeller vanes. Here we go, draining the coolant again.

 

Naw, I'll pay my mechanic to do the diagnostic. I'll want talk to him about next steps if he doesn't find an HG leak.

 

Looking at the plugs is a great idea (they are maybe 30k old). If one looks different, it might mean coolant in the cylinder. But again, I've not seen any white smoke out the tailpipe. Lotsa fun getting the plugs out of an H6…

[1 Lucky Texan]

might need a flexible borescope or something?

 

probably not coolant in the cylinder - but with lower compression and maybe occasional mis-firing - there 'might' be a slight difference in appearance.

 

have you scanned the ECU for 'pending' codes? maybe there is a re-occurring misfire occasionally.

 

but daveT is right, we're always hopeful we can find some way to exonerate the headgaskets - but we're usually wrong. And repeated overheating will only make it more likely HGs will fail if they haven't already.

Edited August 1, 2016 by 1 Lucky Texan

[Caboobaroo]

Do you have any rough running on cold start up? Misfire codes?

 

I've run into a few of these phase 2 EZ30 where the head cracks from the combustion chamber to the cooling jacket.

[Numbchux]

One more easy thing to check, although it sounds unlikely.

 

Remove the upper radiator support brackets, and tilt the radiator back to look for debris in the radiator. I've seen a few (one just last week that was really bad) where the radiator is packed solid, but the evaporator looks clean as can be. I don't understand how that much debris could get through/around the evaporator and end up in the radiator, but it happens. It still doesn't really explain the bubbles, but it might be worth a try.

[Fairtax4me]

Its a head gasket.

Do a leakdown test to confirm.

Combustion tests almost always come up negative on these.

[wirelessenabled]

My 2000 had an occasional overheating problem with the overflow tank filled.  No noticeable bubbles though.  I thought head gaskets.

 

A month ago or so I replaced the radiator with an aftermarket one that cost all of about $65 shipped.  Since then even in near 100 degrees the coolant temp stays near 181 degrees, going up when I stop for a stoplight but almost immediately going back down as soon as I move.

 

The radiator I removed was the original with 220,000 miles on it.  I spent more than 30 minutes blowing all the junk out of the A/C condenser.  It was really packed with stuff.

 

It so far has been a cheap, easy, and 1 hour fix to the overheating problems.

 

It only takes less than 30 minutes to drain the coolant and pull the radiator.  Maybe take a look at that.

[DaveT]

Major difference between overheat with no bubbles & full coolant due to blocked radiator VS low coolant with overheat and bubbles.

[Pauldoug]

I'm trying to find a mechanic that will do these tests, looking for one in northern NJ, or southern NY state.

 

Fairtax4me I'm surprised that you say that a combustion gases test usually comes up negative. They are often recommended, including by this guy: https://allwheeldriveauto.com/subaru-head-gasket-problems-explained. Of course I'll keep your advice in mind.

 

BTW, have had the overheating problem maybe 5 times in the last month & 1/2. (Coolant bubbling more often) I am now avoiding driving the car very far.

 

The radiator is maybe 15k old, so unlikely blocked. No CEL misfire codes, no rough starting (though I recently had a p0021, which went away after 2 drive cycles).

[1 Lucky Texan]

I recall a guy that had replaced a radiator and a piece of paper or cloth was blocking flow - any chance there was a paper towel or similar used to 'protect' an open hose or other cooling connection and was forgotten?

 

anyway - hope you get it sorted - seems like a leak-down test or a chemical test could be a good next move. Fair is correct though - that chemical test is iffy, I have also read reports of it being a 'false negative'.

Edited August 2, 2016 by 1 Lucky Texan

[msmithmmx]

You had me at " often the overflow tank will boil".  Odds are 95% that you have a bad head gasket. 5% chance you have trapped air in the system.

 

[idosubaru]

Sounds just like an H6 or EJ25D headgasket.

 

 

Fairtax4me I'm surprised that you say that a combustion gases test usually comes up negative. They are often recommended, including by this guy: https://allwheeldriveauto.com/subaru-head-gasket-problems-explained. Of course I'll keep your advice in mind.
 

 

I'm not, those tests are easy for anyone to use and available but can easily give false negatives particularly on early failures that aren't huge problems yet (car still drivable, intermittent, etc).

The gas analyzers ($$$$ electrical equipment) that can test for hydrocarbons in the coolant are much better here in the hands of someone who knows how to use them.

 

Radiator needs to be confirmed full, no air, no leaks or the symptoms are somewhat ambiguous. 

 

If those all check out - there needs to be an accurate assessment of "bubbles in the reservoir" and "bubbles in the radiator", and "boiling in the overflow" -

*bubbling* is too ambiguous of a word - it can describe both boiling and bubbling which both mean distinctly different things.

 

Check for obvious things like a clogged radiator, fans, leaks, air - but this is common H6 headgasket territory.

 

Doesn't probably matter - what why was the radiator replaced?

If due to overheating - describe those symptoms. 

If due to failure - how badly did it overheat/loose coolant?

 

[WoodsWagon]

Water pump would be my guess, especially if it cools better if you drive faster. Try manually downshifting the trans to hold it in a lower gear when it gets hot. Does it cool back down even with you maintaining the same speed?

 

If the pump isn't circulating properly, then you will get localized hot spots in the engine where the coolant will boil, even though the whole temp of the engine isn't in the overheating range. That could be what you're seeing in the overflow bottle.

 

 

A water pump vanes are eroded-away - hey, anyone?, can the WP impeller be viewed thru the t'stat hole?)  http://www.subaruoutback.org/forums/66-problems-maintenance/45334-here-s-new-one-trashed-water-pump-vanes.html

[idosubaru]

subaru water pump is unbelievably rare, it doesn't really happen. maybe on an old rusted beater that sat in pure water and salt not running for years and corrded the vanes away but on a 2006 high dollar car with low mileages that's highly unlikely.

 

they ocassionally leak, even that's rare. other than that a subaru water pump failure is so rare it's not even worth diagnosing unless you have some really weird issues....which these aren't weird.

 

the H6's routinely do the temp gauge-varies-by-throttle-input thing and bubbling in the overflow when not overheating - i've seen it multiple times, and i've never seen a failed water pump in 20+ years of Subarus.

Edited August 3, 2016 by grossgary

[AdventureSubaru]

Yeah. I feel like this is just dancing the dance. It's going to be a head gasket job.