Blown head gasket - stick thermostat open?

[Todd H.]

My 97 Legacy GT 2.5 wagon has all the symptoms
of a leaking head gasket listed in this article:

Welcome to Subaru hell. :-\ I've been there.

http://users.sisna.com/ignatius/subaru/headgasket.html

"Common symptoms:
Overheating, often when slowing or stopped after extended high load driving.
The overheating can be seemingly random and sporadic.
Bubbles in coolant overflow reservoir, immediately after running.
Sludgy residue in coolant overflow tank.
Hydrocarbons in coolant overflow tank, this is tested by a mechanic
with specialized equipment and is not evident visually."

According to this additional article:

http://www.smart-service.com/mikesCornerArchive/content-MikesCornerMar06.shtml

it seems that the overheating is caused by combustion gasses in the
cooling system:

"When the gaskets are starting to fail, some of the combustion gasses
(exhaust usually) are forced past the thin metal head gasket into the
cooling system. Little by little these gasses accumulate in the cooling
system and begin to create an "air pocket" if you will, inside of the
engine cooling system. Depending on where this air pocket circulates
to, or how large it is, it can create numerous issues. If it becomes
trapped around the water pump or thermostat it can prevent coolant
from flowing through the engine, which results in almost immediate
overheating."

What I'm wondering is why couldn't I just stick the thermostat open somehow
to keep the engine from overheating. As I understand it, the valve in the
thermostat stays closed to allow the engine to warm up faster after it's
started.

I'd have to imagine that's not a reliable workaround because it would
only address an air pocket issue in/around the thermostat. If the air
pocket airlocks the water pump, you aren't gonna cool the engine, for
isntance.

Another issue is if the leak gets bad tenough, you can get coolant
into your engine which quickly destroys your piston rings ability to
seal the cylinder, and then you're into a REALLY invasive costly
repair to replace rings.

Rebuilding of both heads on my car cost about $1800 at a local
independent.

 

[davel]

My 97 Legacy GT 2.5 wagon has all the symptoms
of a leaking head gasket listed in this article:

http://users.sisna.com/ignatius/subaru/headgasket.html

"Common symptoms:
Overheating, often when slowing or stopped after extended high load driving.
The overheating can be seemingly random and sporadic.
Bubbles in coolant overflow reservoir, immediately after running.
Sludgy residue in coolant overflow tank.
Hydrocarbons in coolant overflow tank, this is tested by a mechanic
with specialized equipment and is not evident visually."

According to this additional article:

http://www.smart-service.com/mikesCornerArchive/content-MikesCornerMar06.shtml

it seems that the overheating is caused by combustion gasses in the cooling
system:

"When the gaskets are starting to fail, some of the combustion gasses
(exhaust usually) are forced past the thin metal head gasket into the
cooling system. Little by little these gasses accumulate in the cooling
system and begin to create an "air pocket" if you will, inside of the
engine cooling system. Depending on where this air pocket circulates
to, or how large it is, it can create numerous issues. If it becomes
trapped around the water pump or thermostat it can prevent coolant
from flowing through the engine, which results in almost immediate
overheating."

What I'm wondering is why couldn't I just stick the thermostat open somehow
to keep the engine from overheating. As I understand it, the valve in the
thermostat stays closed to allow the engine to warm up faster after it's
started.

 

[Rui Pedro Mendes Salgueiro]

What I'm wondering is why couldn't I just stick the thermostat open somehow
to keep the engine from overheating.

Apart from other reasons, an engine with a thermostat always open will
run too cool. This has (at least) the following consequences:

- the engine efficiency will be reduced leading to an increase in fuel
consumption.

- the humidity in the oil will not evaporate, so the oil will be degraded.
This might damage the engine.

As I understand it, the valve in the thermostat stays closed to allow
the engine to warm up faster after it's started.

The thermostat also regulates the engine temperature. Without it the
temperature would increase when the engine is working harder and decrease
when not being pushed.

 

[Rick Courtright]

What I'm wondering is why couldn't I just stick the thermostat open somehow
to keep the engine from overheating. As I understand it, the valve in the
thermostat stays closed to allow the engine to warm up faster after it's
started.

Hi,

If your head gasket's JUST started to leak, this might keep you going
another week or two, but once the gasket's "blown," the compression
pressures will produce gas in the coolant far faster than the cooling
system can handle, even w/ the t-stat stuck wide open.

Do you have a good mechanic or radiator shop near you? Many mechanics,
and most radiator people, have exhaust gas testers that will verify what
you already suspect. W/ Subie head gasket issues being well known, your
analysis is probably spot on.

Best to get it fixed properly ASAP. By "properly," I'm suggesting both
heads come off, get checked at a good machine shop both for warpage and
possible cracks or leakage, and fixed as appropriate (reface the heads
for sure!), then the block be checked for warpage (not impossible, but
far less likely than head warpage, and everything reassembled w/ new
gaskets. You might want to surf a bit to see if any particular
aftermarket brands are recommended that you can find locally (I've seen
some discussions that indicate there are some aftermarket parts that
work better than OEM--I dunno.) Otherwise, OEM gaskets will work.

What you're likely to find is that regardless of the gaskets chosen,
once the heads are refaced, you may never have this problem again. My
machine shop buddy says aluminum heads are notorious for warping until
they're "seasoned" for lack of a better term, then they can be refaced
and will hold their "trueness" from then on (assuming you don't overheat
the engine in the future from some other cause.)

Best of luck!

Rick