99 Subaru Legacy Outback wagon Overheating


Asked by Dec 03, 2015 at 07:10 PM about the 1999 Subaru Legacy 4 Dr L AWD Wagon

Question type: Maintenance & Repair

I have a Subaru 99 Legacy wagon it is overheating.  I changed the radiator
cap and the thermostat.  Ok I flushed the system and put in clean
antifreeze and the fluid that was in it was really brown and nasty.  Now I got
the new thermostat because it was over heating.  Now here are the
symptoms after all that:   I put fluid in radiator and I drive the car, the car
overheats and as it get hotter my heat turns cooler and cooler.  Now when I
take off the radiator cap the water in the radiator is cold and full.  If I let the
car set then all the fluid drains into the motor and the radiator is empty
again.  Now why is the fluid not going into the motor?  Where is the fluid in
the motor going?  It is getting so hot it steams out?  I still don't understand
why the fluid does not switch out with the radiator/motor until the car cools
off??    I read a solution on here about the heater core having air and not
letting thermostat open because its not hot enough, sounds like a good bet
but wanted to know if anyone has advice

10 Answers


Need to bleed the air pockets out of the cooling system...

4 out of 4 people think this is helpful.

Good evening Rowefast !

3 out of 3 people think this is helpful.

And a good evening to you too!

2 out of 2 people think this is helpful.

How was the hoilday?

1 out of 1 people think this is helpful.

Full stomach, sleepy afterward...

2 out of 2 people think this is helpful.

I here you, same here, I gave my dogs some left over turkey and they all fell asleep to...

2 out of 2 people think this is helpful.

Sounds like your water pump is not working. That's why your heat gets cooler. No circulation. If the air bleed doesn't work, I'd replace the water pump.

1 out of 1 people think this is helpful.
Bob Beaman

Probably a blown head gasket. Combustion gases or air get into the system and cause the heater to lose warmth. Have the cooling system pressure tested and checked for combustion gases. Also a compression test may show the problem as well.

1 out of 1 people think this is helpful.

The compression test would show 1 or 2 low cylinders, indicating the bad head gasket, as Bob suggests.

2 out of 2 people think this is helpful.

Faster to check head gaskets with percolation test: Fill radiator if applicable. Remove rad cap; install kitchen funnel in hole fairly snugly. Add water to make nice visual "puddle". Start car and allow to warm up fully, with AC ON (ensure fans operate) Add water to keep puddle visible and stable. After stabilization do you see gas bubbles coming to the surface? Cycle motor up to 2 or 3 k repeatedly as someone watches the puddle. Large air bubbles may ensue until radiator is full (add water as necessary). Sniff air bubbles percolating up with a HC sniffer for definitive analysis to prove gases are hot combustion (blown head gasket) vs just trapped air. Note that first gen (1996-1999) 2.5i (DOHC) motors had seriously weak HG designs; nearly all of them have failed as combustion pressures breached the HG into the coolant bath, causing uncontrollable "percolation". Note also that HG replacement in this "new" design was often followed by rod failure later on if overheating occurred severely. Given age of this Subie I'd trash it. Now the small good news: Aftermarket thermostats for Subies are notoriously undersized, slowing flow sufficiently to cause overheating under stress (highway or uphill). As well, a blocked heater hose will block flow similarly. So back-flushing the rear heater hoses (5 minutes) is a good idea, as well reinstalling your original t-stat (as the OE NEVER fails...it's a really good 'un). There's a small chance your rad itself is clogged, but probably only if someone previously gooped it up with oatmeal or fish pellets (stop-leak additives). So it can be worth a shot to perform the cooling system cleanup above if, after purging all trapped air, percolation of AIR ensues. If percolation of exhaust gases ensues, then of course your HG's are trash. The odds are large that your DHC 2.5i is going to the dump, however, so don't spend much money chasing a new radiator, etc. Here in Subie country we NEVER see first gen 2.5i on the road anymore.

2 out of 2 people think this is helpful.

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