Overheating Subaru Legacy AWD Wagon...

[Ray O]

Way ahead of you, Ray! Brought it for MA state inspection (remember
those?) He put the gas sniffer for the tailpipe in the filler neck and
there were PLENTY of hydrocarbons coming out through the radiator!!!

Yup, I remember MA state inspections. I was driving a hard plated pool
Cressida (not my regular company car)and got pulled over in downtown Boston
for not having an inspection sticker on the car. Since the car was
registered to the company, the officer was kind enough to issue the ticket
to the company instead of me.

As far as the Legacy, my advice is to dump it unless Subaru has made some
kind of improvement in the design to prevent future reoccurrences.

 

[ngt]

1997SubaruAWD wagon, "L" model, basic car.

On the first drive yesterday, I got about 8 miles and it began
overheating, after running static for about 40 mins with no problems. ....

I have been struggling since August with very similar problems with a
'98 Legacy Outback, 2.5L engine. The problem appeared after I
replaced a broken heater hose. To make a very long story short, the
cooling system now seems incapable of handling the transition from
high load, high coolant flow conditions (e.g. highway driving) to
light load, low flow (e.g. suddenly slowing down in traffic). The
temperature gauge will spike from the normal 9 o'clock position to
offscale hot in about 30 seconds. If you see this happening and
immediately place the car in neutral and rev the engine to about
4,000RPM, the system will usually recover, with the temperature gauge
dropping back to below 9 o'clock within 30 seconds. If you don't
catch it fast enough, the coolant will boil over. The car has no
problem cooling during extended driving in stop and go traffic on hot
summer days, only the transitions bother it. It appears the
thermostat can't open fast enough to deal with the changing load- but
no thermostat is going to respond on a timescale of seconds. The
cooling system was pressure tested by a local garage, who found no
problem. Drilling a few 1/8" bypass holes in the thermostat flange to
allow some coolant flow even when the thermostat is closed seems to
have provided a solution to the problem, but with temperatures often
going to -20C here the engine doesn't warm up properly. (It's worth
noting that in a post a few years back the owner of a used Legacy of
this vintage discovered the thermostat had been removed, and found
overheating problems when a new thermostat was installed). I have
filled the cooling system as slowly and carefully as I can, including
extended running at idle with the radiator cap off to "burp" the
system. The burping seems to go on for a long, long time, suggesting
it is very difficult to get air out of the system. If anyone has a
solution to this strange problem, I'd really appreciate hearing it. In
the meantime I'm living with the bypassed thermostat.

Garry

 

[clifto]

I have been struggling since August with very similar problems with a
'98 Legacy Outback, 2.5L engine. The problem appeared after I
replaced a broken heater hose. To make a very long story short, the
cooling system now seems incapable of handling the transition from
high load, high coolant flow conditions (e.g. highway driving) to
light load, low flow (e.g. suddenly slowing down in traffic). The
temperature gauge will spike from the normal 9 o'clock position to
offscale hot in about 30 seconds. If you see this happening and
immediately place the car in neutral and rev the engine to about
4,000RPM, the system will usually recover, with the temperature gauge
dropping back to below 9 o'clock within 30 seconds. If you don't
catch it fast enough, the coolant will boil over. The car has no
problem cooling during extended driving in stop and go traffic on hot
summer days, only the transitions bother it. It appears the
thermostat can't open fast enough to deal with the changing load- but
no thermostat is going to respond on a timescale of seconds.

This sounds very much like what happened when I changed the thermostat in
my '94 Acclaim 3.0L. I found that the old thermostat had a considerably
bigger orifice; I believe the smaller orifice on the new 'stat is
restricting flow somewhat.

 

[Carl 1 Lucky Texan]

I have been struggling since August with very similar problems with a
'98 Legacy Outback, 2.5L engine. The problem appeared after I
replaced a broken heater hose. To make a very long story short, the
cooling system now seems incapable of handling the transition from
high load, high coolant flow conditions (e.g. highway driving) to
light load, low flow (e.g. suddenly slowing down in traffic). The
temperature gauge will spike from the normal 9 o'clock position to
offscale hot in about 30 seconds. If you see this happening and
immediately place the car in neutral and rev the engine to about
4,000RPM, the system will usually recover, with the temperature gauge
dropping back to below 9 o'clock within 30 seconds. If you don't
catch it fast enough, the coolant will boil over. The car has no
problem cooling during extended driving in stop and go traffic on hot
summer days, only the transitions bother it. It appears the
thermostat can't open fast enough to deal with the changing load- but
no thermostat is going to respond on a timescale of seconds. The
cooling system was pressure tested by a local garage, who found no
problem. Drilling a few 1/8" bypass holes in the thermostat flange to
allow some coolant flow even when the thermostat is closed seems to
have provided a solution to the problem, but with temperatures often
going to -20C here the engine doesn't warm up properly. (It's worth
noting that in a post a few years back the owner of a used Legacy of
this vintage discovered the thermostat had been removed, and found
overheating problems when a new thermostat was installed). I have
filled the cooling system as slowly and carefully as I can, including
extended running at idle with the radiator cap off to "burp" the
system. The burping seems to go on for a long, long time, suggesting
it is very difficult to get air out of the system. If anyone has a
solution to this strange problem, I'd really appreciate hearing it. In
the meantime I'm living with the bypassed thermostat.

Garry

It certainly sounds like you're doing a lot of the right things.

Um, are you certain the 'burping' is done with the heat set on 'max' and
have you changed the radiator cap?

Can't really think of anything else - maybe someone will have some more
suggestions.

Carl

 

[Sam]

I had a very similar problem once on my 98 outback. It ended up being
the thermostat - I changed it once because the car wouldn't heat up
and then it began overheating. It turned out to be a faulty
thermostat so i got an OEM one from the subaru garage and it solved my
problems. Although, you've already replaced your thermostat I'd
recommend trying a second one - I was about ready to replace my water
pump and had already had my radiator checked for blockages before I
changed the thermostat a second time. According to the radiator shop
where I had my radiator checked, faulty thermostats are common - the
guy told me a story of having to buy four once before getting one that
worked.

 

[ngt]

I tried a new radiator cap- no improvement. I've been "burping"
parked on a steep incline with the rad higher than the engine and the
heat on max, although I think coolant always circulates in the heater
core no matter what the heater setting.

The new thermostat (second source) and the Subaru original showed
identical behaviour when heated in water, both opening nicely at the
temperature stamped on the thermostat. I suspect both are working as
designed. The Subaru thermostat has a slightly larger aperture.

The car is not consuming coolant so I think the head gasket is OK.

Even after repeated "burping" sessions there are still bubbles
appearing, so I suspect it is very difficult to bleed the air from the
system.

Thanks,

Garry

 

[Mike53]

<SIGH> It was up on ramps...BHG I'm afraid...

Look under Subaru thermostat operation I might be able to help

 

[Mike53]

It certainly sounds like you're doing a lot of the right things.

Um, are you certain the 'burping' is done with the heat set on 'max' and
have you changed the radiator cap?

Can't really think of anything else - maybe someone will have some more
suggestions.

Carl

There must be something wrong with the heater hose Read subaru
thermostat operation Michael