Help, another Subaru that overheats. Head gasket?

[subieman]

I would like to get anyones opinion for my overheating problem. I'm thinking head gasket...

 

The temperature in Reno is been over 100 degrees for the past few days, so I have been running the AC on my 90 Legacy. Temp gauge always stays in the middle... never moves. But yesterday I noticed it climbing to the 3/4 mark while I was climbing a hill. I killed the AC and slowed down, the engine was pinging like mad, so I slowed down more. I made it over the hill and started to coast down the other side and the temp gauge stayed at the 3/4 mark. Strange.

 

Popped the hood when I got home and noticed both fans were running. (good) But the upper radiator hose had no pressure, it was almost sucked in. Lower hose had pressure. Overflow was full and bubbling like mad. This is when I thought head gasket. Turned the engine off and let it cool a little. Still bubbling in the over flow and the upper hose was still flat. I opened the radiator cap, just about killed myself there was so much pressure on that side. I filled the radiator up and started the engine without the cap on. Coolant must have shot out 4' in the air.

 

2 hours later I started her up and drove around the block, everything seemed fine (except for the pinging) and the upper hose had pressure again. But the cooling fans never would shut off. Gauge was at 1/2.

 

I'm screwed huh?

 

Let me know what you guys think.

 

Damn that was long winded!!!

[nipper]

Slow down...

 

First off, when was the last time the coolant system was serviced? It's often overlooked. You need to start off with the cheapest thing first, a new radiator cap. Next the thermostat and fresh fluid.

 

Lets cross our fingers that you didnt blow a HG due to a coolant issue. Sometimes the egg comes first, sometimes the chicken. Either way both need to be addressed even if the HG failed.

 

nipper

[subieman]

The one thing that is worrying me is the bubbles in the over flow.

 

The Coolant was changed last year when I had the engine out, but I never replaced the thermostat or cap.

 

I just changed the thermostat, radiator, coolant, water pump, hoses in my 88GL. It was overheating, but never blowing coolant out of the filler like the Legacy is.

 

The Legacy has 180k on it, so I'm sure the radiator is ready to be replaced. Maybe a plugged rad is causing the weird pressure issues?

[OB99W]

[...]Turned the engine off and let it cool a little. Still bubbling in the over flow and the upper hose was still flat. I opened the radiator cap, just about killed myself there was so much pressure on that side.

With the engine off for a while, it was still bubbling? Those bubbles obviously weren't exhaust gas, but steam from boiling coolant; the engine must have been darn hot. Since the upper hose didn't expand right away, it's also obvious that there wasn't much flow through the radiator from one side to the other.

 

 

I filled the radiator up and started the engine without the cap on. Coolant must have shot out 4' in the air.

You might think that was caused by exhaust gases, but with a very hot engine, unpressurized water (I'm assuming that you didn't add any "antifreeze") could boil just about instantaneously when it hit a hot spot, causing the geyser; even a proper coolant mix could, given enough heat.

 

 

2 hours later I started her up and drove around the block, everything seemed fine (except for the pinging) and the upper hose had pressure again. But the cooling fans never would shut off. Gauge was at 1/2.

Still pinging and both fans still running after cooling down for two hours? As I said, darn hot engine.

 

 

I'm screwed huh?

 

Let me know what you guys think.

I'm with Nipper, slow down.

 

 

Damn that was long winded!!!

You mean, unlike my posts?

 

 

[...]The Legacy has 180k on it, so I'm sure the radiator is ready to be replaced. Maybe a plugged rad is causing the weird pressure issues?

What else could explain the pressure difference between radiator tanks, especially with the engine not running?

 

Of course, if a radiator plugs suddenly, there's a question of what caused it. In an old radiator, there are often deposits that already narrow the tubes and limit the flow. It sometimes doesn't take much more to plug them almost completely, and "gunk" caused by a bad HG can do that. However, sometimes an engine that's overheating can cause deposits in the cooling system to loosen (the heat and pinging can help knock some material free) and they wind up at the radiator tubes, further clogging them and creating a rapid upward temperature climb. If that's what happened, your heater core might have the same problem. Without proper flow, thermostat operation is compromised, making the problem even worse.

 

By the way, what ratio of "antifreeze" to water do you normally run?

[subieman]

Thank you for that very detailed post, you have assured some hope in this car.

 

I will start with the cooling system, radiator, thermostat... then go from there.

 

I use the 50-50 pre mixed stuff.

[OB99W]

Thank you for that very detailed post, you have assured some hope in this car.

You're welcome; hope is a good start.

 

 

I will start with the cooling system, radiator, thermostat... then go from there.

Sounds good to me. But first let things cool down completely, make sure the radiator and recovery tank are properly filled, then verify that none of the bubbling/pinging/fan-running problems crop up immediately on start-up, just to be sure. Obviously, don't run it very long until the overheating cause is resolved.

 

 

I use the 50-50 pre mixed stuff.

That should give decent boiling point elevation, especially if the system is otherwise okay.