Bubbles in coolant reservoir when running and random overheating.

[szymon]

Hi all,

 

I have a 1991 Subaru Legacy LS with 246000k on it. The vehicle have overheated on me twice over a period of one month. Each time a bunch of coolant leaked out through the overflow hose. After refilling the radiator and and the reservoir the car runs fine.

 

The oil which I have changed about 650 km ago is clear/light brown. The oil is synthetic. Both of the fans turn on when the engine is hot so I conclude the thermostat and fans are working properly. When the engine has warmed up and idling there is bubbles visible in the coolant reservoir. It looks like the bubbles are mainly in the proximity of the hose connecting to the radiator. The coolant is green color but there is light/moderate black residue on the inside of the reservoir.

 

What could the problem be? Any suggestions on how can I diagnose it?

[GeneralDisorder]

Likely the head gaskets are blown and are pushing combustion gasses into the cooling system - causing it to overpressurize and force the coolant into the overflow bottle.

 

Either that or the radaitor cap is bad. You can try replaceing it but they don't often fail.

 

GD

[ericem]

It is also not often for a 91 with the EJ22 to have a headgasket go bad. But if it still had the original coolant from 91 it will loose its property and could corrode the gasket causing them to leak.

[MilesFox]

you probably have a failing water pump which lead to the overheat, which led to bubbles in the coolant, which are indicative of a head gasket failure(beginnings of it)

 

you will have a high probability of success using a block sealer, such as k&w brand to buy you time for a repair.

 

do you know the service history of the car?

[szymon]

GeneralDisorder, could you explain to me how would a faulty radiator cap cause all these symptoms?

 

Thanks to you all for help.

[szymon]

Can anybody confirm that a 1991 Subaru Legacy LS 2.2L Non-Turbo needs a radiator cap with rating of 13 lbs?

[Rooster2]

I had a 91 Leggie with the 2.2 that blew the head gasket, so it can and does happen. I had a about 175K miles on the odo, so I swapped in another 2.2.

[ericem]

Can anybody confirm that a 1991 Subaru Legacy LS 2.2L Non-Turbo needs a radiator cap with rating of 13 lbs?

 

Just go to the dealer for a OEM cap it is only $10.

[GeneralDisorder]

GeneralDisorder, could you explain to me how would a faulty radiator cap cause all these symptoms?

 

Thanks to you all for help.

 

If the cap doesn't hold to the specified system pressure of 13 lbs it would open and dump pressureized coolant into the overflow bottle. The loss of system pressure and the loss of coolant causes overheating as the coolant boils - creating steam bubbles that escape into the overflow (the bubbles you are seeing). Steam doesn't transfer heat and at some point you lose flow through the system as there is not enough left for the water pump to push it through the block and back to the radiator inlet.....

 

And yes 0.9 Bar, or 13 psi is the rating for the cap.

 

GD

[Mike104]

2.2L are not noted for bad head gaskets but any engine "can" have a blown head gasket. Rad cap is cheap solution. If that doesn't work do the chemical test for combustion gases in the coolant.

 

At 246k miles the water pump could also be the culprit and or a clogged heater core (or is that just the 2.5L?). Try the simple stuff first. Rad cap, combustion gas test (in that order). If you add the block sealer, disconnect the hoses from your heater core and connect them with a fitting to prevent the heater core from getting clogged. You can reconnect them after the sealer has been run through for a day or so.

[szymon]

I have changed the radiator cap today but the bubbles are still there.

 

I took the car on a 15 minute ride up a hill. When I arrived at my destination I have noticed that the coolant reservoir is full all the way up to the yellow rubber cup. It was very close to overflowing. The temperature gauge was reading normal working temperature all the way up the hill.

 

I then drove back home, all the way downhill, I have not been accelerating, only braking to slow down from time to time. At the very bottom of the hill I have noticed the engine temperature climbing above normal. I turned on the heater inside the car to blow hot air at full blast, but the air was cold. I tried switching the heater to blow cold air and then back to hot air but it did not do anything. The heater was not blowing hot air even though the temperature gauge was indicating that the engine in hot.

 

I pulled over. The radiator fans were both working. You could feel warm air blowing on the driver's side of the grill in front of the hood, but the passengers side was cold. The coolant reservoir was still filled almost all the way up to the rim, but has not started overflowing yet. What was weird is that the engine did not look very hot. I could not feel the heat radiating from it as much as when I have just reached the top of the hill. The thick black rubber hose connecting the engine to the radiator on the passengers side was warm but not hot like when I have just finished climbing a hill.

 

I got back in to the car and started driving again. I was on a flat now so I had to accelerate to get the car moving. I could feel the air coming from the heater becoming warm. The very last section, about 50 meters long, I had to ride up a very steep hill, the air that the heater was blowing out was warm. It was surprising to see the temperature gauge oscillate relatively fast during all of this was happening. It would climb up quite fast and then quickly drop as i stopped.

 

The car have overheated twice before. Both of these times I just finished driving downhill and just hit the flat section of the road. The A/C is disconnected in this vehicle.

 

Does anybody know what to think of this strange behavior?

 

I really appreciate you help guys. Thanks a lot.

[Mike104]

Have you eliminated the combustion gases in the coolant? This step is vital to confirm or rule out a suspected HG leak. You can use either a chemical test or an electronic gas analyzer.

 

Leaking of combustion gases into the coolant system can cause the coolant to flow into the overflow tank. Cool air from the heater when the engine is hot is an indication that there is either low coolant level (can be caused by an air bubble in cooling system) or the heater core is blocked.

 

Since you have ruled out the rad cap, those would be my next two steps.

[Gloyale]

System filling with air(gases) from blown headgasket.

 

Pushes out coolant

 

When coolant is low, and car ointed downhill, the "bubble" collects in the heater core as it is the highest place. Hence the cold air blowing.

 

CLASSIC subaru headgasket failure.

 

Sorry. Good news is hte EJ22 is super easy to replace HEadgskets on, and you can use felpro gaskets with confidence. If it was a 2.5 you would HAVE to use OEM subaru gaskets.

[MilesFox]

classic head gasket symptoms.

 

you can get away with adding coolant daily, and run with the rad cap loose so it doesnt push all the coolant out(it lets the pressure escape)

 

i had a 88 sedan with a blown head gasket and ran it with the cap loose. i would run the heat full blast, and when it got cold, it was time to add coolant.

 

if the temp is spiking, let the car cool down before adding coolant or it will geyser all over you. leave the car run when you add coolant.

[Markus56]

it was already said, but i'll bet the waterpump is bad. no hot air from the heater core means either the heater core is plugged, or the coolant is not cycling. I would put money that the coolant never got replaced and it dissolved the impeller in the pump. That *might* also be the cause of the bubbles, but the head gasket is probably blown. Do a chemical test on the coolant to find out for sure(as already stated).

 

Good Luck!

[szymon]

Blown gasket would explain the why the engine in misfiring. I just bought this car month and a half ago from a family friend who is a mechanic. Bought it for $2500. It was misfiring badly, one of the cylinders looked bad in a compression test and my mechanic have disengaged A/C which significantly improved how the engine is working. He looked at the car ofter it had overheated on me once, but said he could not find anything and that the car works fine in his opinion. Unfortunately I cannot go back to see him because i am 700 km away now.

 

I am contemplating whether it is worth to put more money into this machine. The car seems to be in exceptionally good shape for a 91 (except all the mechanical isses mentioned above...) What is the life expectancy on these engines? Do you think it is worth to get the head gasket changed for $1350?

[Markus56]

you could get another motor for a third of that