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Kevin C.
Kevin C., Subaru Master Tech.
Category: Subaru
Satisfied Customers: 1727
Experience:  34 years of Subaru service experience, ASE Master Technician.
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I own a 2006 Subaru Outback wagon 3.0 liter R, 130k miles.

Customer Question

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.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. 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 have never allowed the temp gauge to go all the way to red. The one time the needle touched the red line, I pulled over and stopped the car). 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 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.Yesterday, 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.Oh, and one more thing: 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?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 a leak causing the coolant to boil (because the system never completely pressurizes)? What's the next step? Pressure test the radiator?As a reminder: new hoses, new Subaru thermostat, new Subaru radiator cap, recent radiator, Subaru coolant (50-50 mixture with distilled water). Subaru OB, 2006, 3.0 liter, 6 cyl.
Submitted: 1 year ago.
Category: Subaru
Expert:  Chad Farhat replied 1 year ago.

Hi, I'm Chad ,Welcome To JustAnswer, I'm reviewing your question and I will be be posting a replay ASAP

Customer: replied 1 year ago.
Hello Chad.
Expert:  Chad Farhat replied 1 year ago.

hey how are you i m reading your comments just give me few more minutes

Customer: replied 1 year ago.
Good, no problem, take your time. A lot to read.
Expert:  Chad Farhat replied 1 year ago.

ok thanks

Expert:  Chad Farhat replied 1 year ago.

the symptoms do indicate a head gasket but me before i say that ,there is other areas need checking ?

1-If in city traffic the issue is evident ,a weak water pump will cause this , when you at city driving obviously water pump turning slower and coolant is circulating slower , when you take off on highway the temp drops and stays where it need be ? i m i correct on that ?

Radiator is what you thinking will also be an issue if it partially clogged , getting a heat gun laser tester and check the coolant temp from both outlet of the radiator , how much is the radiator is cooling the water down ?

i got more but answer this for me :)

now obviously this a little harder problem so it might take a little back and forth and some testing on your part, which you definitely seem you know your stuff, and i m glad for that since it will help both of us .

Expert:  Chad Farhat replied 1 year ago.

have you pulled the dipstick and see if any oil & water is mixing , i doubt it but i have to ask you , i want to cover every thing , no matter how insignificant it is ,so we can be accurate in our diagnostic

if you put your hands on back of tail pipe, not smack on it but very close with an open palm and wait few secs , it will be hot but is there evidence of coolant on your hand

or sometimes you can even smell it

Customer: replied 1 year ago.
Chad, thanks for asking those questions, I should have answered them before. No mixing of oil and water. Not on dipstick, oil cap or radiator cap. No coolant coming out of tailpipe.
Customer: replied 1 year ago.
I should have said that at one point I had flushed out the radiator and the heater core (by running water in both directions directly into the heater hoses).
Customer: replied 1 year ago.
I don't have access to a heat gun laser tester. But I could certainly feel the difference in temp between upper and lower hose. I'll try that.
Customer: replied 1 year ago.
But, lets
Customer: replied 1 year ago.
Ignore that
Customer: replied 1 year ago.
It could be the water pump, but I'm told that bad water pumps are usually noisy.
Customer: replied 1 year ago.
But let's go back to the boiling coolant. A test showed that there are no combustion gasses present.
Expert:  Chad Farhat replied 1 year ago.

not necessarily noise , it will be if the bearing is completely shot but if it only started the engine noise will cover it

sorry my internet went out for few minutes

Customer: replied 1 year ago.
No problem, these things happen. But a bad water pump doesn't explain the boiling.
Expert:  Chad Farhat replied 1 year ago.

as far as your question on exhaust gasses not present and that is a definitely not a head gasket , i m afraid that is not the case.

it depends where the leak is on the head gasket between the head and the block , if the gasket is bad on the part where it covers a water jacket or tube or what ever you want to call it, this air will be present at the coolant jug only ,and you want see it anywhere else and that is what you see bubbling of that is the case

now if the water pump is not cooling the engine enough at idle then it will cause over heating and the jug bubbles will be not from a head gasket , but just because the water reach boiling point

the water pump needs checking , but really there is not a good test for water pump other than what i told you about temp drops when going faster or evidence of water pump bearing making noise ,

if water pump is okay , the only thing left is a head gasket , or what we call a beginning of a head gasket.

Customer: replied 1 year ago.
Ok, interesting. Some additional info. I have never seen the intermittent overheating when the car is started and idles. I've let it run for 20 minutes, and the needle moves to its middle position and stays there. If the water pump were bad, wouldn't the needle start moving to red every time? On the other subject, I do understand that an HG leak can be in different places. For example, depending on the position of the leak, it could allow coolant to leak into the oil, or vice verse. So you're saying that in my case, an HG leak could allow air into the cooling system, but not necessarily combustion gasses from a cylinder into the cooling system?
Expert:  Chad Farhat replied 1 year ago.

yes that is what i think is happening here

Customer: replied 1 year ago.
Would it be worth pressure testing the radiator?
Expert:  Chad Farhat replied 1 year ago.

yes you can , it want hurt, you can leave the tester on radiator and let here run and get to operating temperature and see if the needle start shaking.

Customer: replied 1 year ago.
Ok, I can rent one for free.
Expert:  Chad Farhat replied 1 year ago.

ok just let me know

I m online usually from 10 am till 12 pm

just let me know

Chad (aka-Jhook1398)

Customer: replied 1 year ago.
Expert:  Chad Farhat replied 1 year ago.

cool will talk later