Bubbles in overflow, "sniff" testing negative.

[quikveedb2]

'92 Legacy L, manual, wagon, 199,xxx miles. New timing belt/water pump done around 196k according to PO. Bought back in October of last year, driven all winter relatively problem free with one exception when about a month after purchase when the car started to run warm on my commute to work, never getting past 3/4 on the temp gauge before I pulled over since I know how sensitive head gaskets can be. I found no coolant in the overflow so I filled it, and once home without issue followed the procedure to burp the motor & remove any remaining air. I watched the level religiously all winter and saw hardly any change either up or down until a recent trip down to Denver that involves a pretty serious mountain pass and a couple hours on the highway. When I reached my destination I checked the overflow and the level had risen 1.5-2 inches and there were bubbles coming out pretty consistently. A few hours later when I checked the level cold it was back where it has stayed since late last year. I decided to err on the side of caution, call AAA, and have them tow the car back up since the drive involves 6000-plus feet of climbing to get back to my home in the mountains. Now during none of this did the cluster indicate that anything was awry with the motor, the gauge sits just below the 1/2 way point, including sitting at idle, in traffic, on the highway, and even on the drive down to Denver on said mountain pass. If anything I felt like it ran on the cold side all winter, taking some time to get up to temp & cooling down pretty quickly driving downhill.

 

Here's a link to video of the overflow with the car up to temp after driving for a while;

http://vimeo.com/95927224

 

I borrowed a "Block Check" tool from a friend & pick up some test fluid from NAPA to see what I could find. I tested when the motor was idling cold, again at running temp according to the gauge after idling for a while, and again after a 20-30 minute drive at normal speeds & load and all cases I was not able to get a positive test result. I've swapped the radiator cap to a new unit and I can still visibly see bubbles in the overflow.

 

I'm kind of stumped. I guess the next steps would be to do some compression tests, and I've heard that there are test strips to check the coolant to see if maybe I'm just getting bad results from the sniffer. Any ideas?

[Fairtax4me]

Compression test won't tell you anything. Need to do a leak-down test.

 

Check for pressure in the upper radiator hose after running for about 15-20 seconds after the first start in the morning. That's usually a first sign of head gaskets, not many people notice it.

[1 Lucky Texan]

previous owner may have installed a deficient type of thermostat.

 

[darsdoug]

Bad head gasket with combustion gases leaking into coolant passages. Replace HG's.

[Rooster2]

Bad head gasket with combustion gases leaking into coolant passages. Replace HG's.

Bubbles in the over flow is a positive sign of bad head gaskets. The head gasket goes bad allowing exhaust gas to enter the cooling system. The bubbles you see are formed by the exhaust gas. This is so typical of how head gaskets go bad in a Subie. All three Subies I have owned ( 91, 98, and 99) had head gasket trouble; all three had bubbles in the over flow.

[idosubaru]

Check simple things first:

 

1. replace the radiator cap - i'd want a new Subaru cap on there anyway, so replace it now.  I think a failed gasket at the base can also cause pressure/bubbling/fluid movement issues.

 

2. make sure there are no coolant leaks.

 

3.  may simply be loosing coolant slowly over time and the level isn't staying within range in the overflow tank?

 

I have seen EJ25's with bad headgaskets fail the hydrocarbon test, though it should fail it and it should fail it if it's been doing it for a few months.

 

If it ends up being the headgasket, you can almost bet your bank account you bought it with bad headgaskets, since EJ22's never fail unless they've been overheated.  Wouldn't surprise me if the overheating prompted the water pump/timing belt job before you bought it.

[heartless]

previous owner may have installed a deficient type of thermostat.

 

or no thermostat at all if it takes a while to warm up, and cools quickly....

 

I second grossgary's advice.

 

Make sure it has either an OEM Subaru thermostat, or a Stant Exac-stat, part number 48457

Burp cooling system properly on refill, new radiator cap, and see how things go.

[quikveedb2]

Thanks for the replies. I do have an OEM thermostat ready to install so I'll try that, though I don't understand how a thermostat would create the bubbling?. I'm surprised that the hydrocarbon test is coming back negative, considering the amount of gas I'm seeing in the overflow.

 

Check simple things first:

 

1. replace the radiator cap - i'd want a new Subaru cap on there anyway, so replace it now.  I think a failed gasket at the base can also cause pressure/bubbling/fluid movement issues.

 

2. make sure there are no coolant leaks.

 

3.  may simply be loosing coolant slowly over time and the level isn't staying within range in the overflow tank?

 

I have seen EJ25's with bad headgaskets fail the hydrocarbon test, though it should fail it and it should fail it if it's been doing it for a few months.

 

If it ends up being the headgasket, you can almost bet your bank account you bought it with bad headgaskets, since EJ22's never fail unless they've been overheated.  Wouldn't surprise me if the overheating prompted the water pump/timing belt job before you bought it.

 

New radiator cap already installed. I've been watching closely for leaks & haven't seen any, I think in the 6 months of ownership I think I'd have noticed something by now, or at least the overflow level changing?

 

 

Compression test won't tell you anything. Need to do a leak-down test.

Check for pressure in the upper radiator hose after running for about 15-20 seconds after the first start in the morning. That's usually a first sign of head gaskets, not many people notice it.

 

Excuse me, I did mean leak-down. Can you be more specific about what you mean by pressure? The system pressurizes slowly as the car warms up, as far as I've noticed, the hose is firm & warm to the touch after running for a while. Do you mean that the hose will get hard really quickly from the pressure of the gasses filling the cooling passages before the thermostat opens?

[Fairtax4me]

Right, when the system is cold there will be no pressure in it. It should stay that way until the engine starts to heat up. If there is pressure in the system after only 15-20 seconds of running while the engine is cold its because of combustion gas being forced into the cooling system.