Pauldoug

This problem on my 2001 Legacy sedan 2.5 AT started out slowly and subtly, but recently got much worse. I noticed beginning about four months ago when I was at a stopped at an intersection the headlights would change in brightness every few seconds very slightly. I also noticed that at the same time that the dash lights were doing the same thing, but again very slightly. Stepping on the brake or turning on the highbeams changed the rate of the flickering. Also it didn't seem like this was happening all the time. Now, more recently, the flickering was much more pronounced. I begin to see this happening all the time. If I was driving along at night, for example, the lights would be flickering constantly. I noticed that the idle was affected as well now – the car would buck slightly when coasting. I started to deal with the problem by confirming that all the ground wires were OK. I went to each connection on the body and cleaned and sanded the contacts, applied dielectric grease, and reattached them. Couldn't hurt, but didn't solve the problem. Next went to the local AutoZone to have the electrical system checked. The employee told me that my battery was not good, but that the alternator and voltage regulator were fine. I was a little surprised that the battery was bad, because I never had trouble starting the car. But, considering that it was was over seven years old, I figured it was at the end of its useful life. So I replaced it with an Interstate battery I got at Costco. Unfortunately, that didn't fix the problem either. I decided to do my own test. I started the car and attached multimeter leads to the corresponding posts on the battery, and set the dial to 20 V DC. Sure enough, the voltage was fluctuating rapidly, +/- .5 volts, I think (so much for the free analysis at AutoZone!) It seemed to me that the only possible explanation left was that the voltage regulator was going bad. Since the voltage regulator is part of the alternator, I would need to replace it. The existing one was about 35,000 miles/3 1/2 years old, which is kind of early for an alternator to go bad. That explains why I didn't think at first that the alternator was the problem here. It was not the original – it was a rebuilt replacement I had installed myself, made by USA Industries. Installed a brand new one (DB Electric), which actually cost less than the one it replaced, and that did the trick. No more flickering, idle is smooth again. Hope this helps anyone having a similar problem.

Grossgary: I certainly didn't mean to make this into a game, but point well taken. OK, here it is: there turned out to be a lot of air trapped in the system. First of all, the test for combustion gases, tested on my car that had been driven for 50 minutes (and cooled enough so the cap could be taken off) was negative. The tech then asked me about 20 minutes into their test if the coolant had been changed recently, and I answered that yes, I had done it within the last month or so. The operant word is "I". They were suspecting trapped air, because they noticed that with the heat on, the temperature coming out of the blower was going up and down. Later, he and a partner burped the system to an extent that I hadn't. With a large funnel on the radiator, filled with coolant mixture, one of them revved the accelerator repeatedly while the other squeezed the hoses and added to the funnel as needed. This went on for about twenty minutes. During this time the tech told me that quite a bit of air bubbled out. After that was finished, he monitored the coolant temp with the Snap-On diagnostic tool, idling and revving, and took the car for a 10-minute test drive. The temp stayed at exactly at 205° the whole time. Mike at AZP told me even if it had moved up a couple of degrees, they would go back to suspecting a HG leak. It never did. Total cost for this diagnostic, air purge and test drive: $115. Mike told me that at AZP, when they do a coolant refill, they only do it using the vacuum method. I then took a trip in the car -- 1 hour, then another hour home. No overheating, no coolant overflow tank overflow. A key here is that that yes, I had burped the system after I replaced the thermostat and refilled, but I didn't do it long enough or correctly. Next time, I'll park the car uphill, and have someone else gun the engine periodically while I do the fill (having first warmed the engine enough to open the thermostat). And I'll keep at it as long as it takes. BTW, I've noticed that in the past a few people on this forum have asked for a suggestion for an independent mechanic in northern NJ. I highly recommend these guys: azpinstalls.com. Thanks again for everyone's comments.

Ok: I took the car to a well-respected Subaru repair facility - AZP Installs in Kennilworth, NJ (azpinstalls.com). Took 50 min of highway driving to get there, so the car was warmed up. They tested for HC, and watched the coolant temp with a Snap-On diagnostic tool. Test drove the car. Verdict: Not the head gasket, not a cracked head. In a few days, I'll post what it was, thought in the meantime some of you would want to take another stab at what it was. Two hints: at least one of you guessed correctly. 2. Re-read my posts. A couple of things I mentioned turns out to explain what happened.

Let me answer a few questions. The radiator was replaced as a result of a fender bender to the front left of the car, about two years ago. The body shop guy told me that they had finished all the work and they noticed some kind of minor damage on the radiator that made it unusable. I don't remember what he said. In fact they might've broken it when they were doing the work. So the original radiator was otherwise sound ( presumably not clogged, not leaking). As for the "bubbling", sometimes I'll see that there are a few bubbles in the overflow ( like gently blowing into a straw that's immersed in water), and the coolant level in the overflow is normal. Perhaps this is when the condition is just starting. Other times, I'll open the overflow, and the coolant will be very high and at what appears to be a rolling boil. This often will continue for almost a minute after the engine is turned off. Note that the car is not always overheating at this point, ( actually, usually not) by which I mean the temperature gauge is at dead center. I'm working to get the car in at an independent Subaru repair place I found in northern Jersey. It's run by true Subaru enthusiasts. So they should really know the car very well. They do list a leakdown test as one of the services they offer. I'm hoping they're not on vacation; I'm waiting for a call back. Meantime, I'll be glad to answer any other questions or clarify anything I've said before. Thanks for all the advice so far.

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 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…

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.

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.

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.

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?

I had to the same issue on my 2006 OB R. I got under the car while a second person pushed up and down on the rear of the car. Turned out to be the BUSHING-TRAILING LINK,REAR, as the part is called in the online catalog. The trick is getting the old bushing pressed out and the new one in. Getting the old one out wasn't hard (rented a tool for it at Autozone). I pressed in the new one with my vice. Not easy. Next time I'll put the bushing in the freezer first. Warning: the locking nuts on the bushing bolts were almost impossible to get off, even after plenty of PB Blaster. I had to cut into one of nuts to free it. The guy at the dealer parts dept. said the mechanics always put a torch to the nuts before attempting to remove them. So order some extras. This was a time-consuming (but cheap) repair. I'd change the corresponding bushing on each side of the car, even if its twin isn't sqeeking now.