1998 Subaru Legacy thermostat

Tiny
BABYCARLOS
  • MEMBER
  • 1998 SUBARU LEGACY
  • 4 CYL
  • AWD
  • MANUAL
  • 213,000 MILES
I have a 98 subaru legacy outback that's been giving me some problems lately. One day the car started to overheat, so I touched the upper rad hose and the lower rad hose and came to the conclusion that the thermostat was sticking because the lower rad hose was cold while the upper was hot. I replaced the thermostat, filled the rad with anitfreeze 50/50 mix, and I still had the same problem. I removed the thermostat and the problem was gone, but ofcourse there was no heat and the car never warmed up. The water pump isn't failing because if you rev the engine with the rad cap off antifreeze will shoot up. Could there possibly be air in the system, and if so how do I bleed it?
Saturday, November 22nd, 2008 AT 12:27 PM

7 Replies

Tiny
JAMES W.
  • MECHANIC
  • 2,394 POSTS
Not to cry wolf, but a leaking head gasket will cause the same thing. Is your cooling fan working. As far as air in the system, it should purge itself out after a couple of "warm up/cool down" cycles. Try letting the car sit at a warm idle and watch the radiator fill neck. You should see a few bubles at first, but then none. If you have continuos bubbles, after 5 or 10 minuetes, it may be head gasket. Another test for headgasket is; let the car sit overnight. Next day, pull the plugs and crank it over looking for water coming out of a plug hole.
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Saturday, November 22nd, 2008 AT 5:03 PM
Tiny
BABYCARLOS
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  • 5 POSTS
Well it turned out to be the head gasket. But it was a small leak so I decided to try blue devil head gasket repair and guess what? It worked!
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Sunday, November 23rd, 2008 AT 1:49 PM
Tiny
JAMES W.
  • MECHANIC
  • 2,394 POSTS
Glad to hear it. Keep in mind, a sealer is usually only a tempory fix. You only have about 14 lbs coolant pressure verses 100+ lbs of compression.
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Sunday, November 23rd, 2008 AT 9:15 PM
Tiny
BABYCARLOS
  • MEMBER
  • 5 POSTS
Ok so now my uncle has a 91 blazer s10 4.3L which had the same exact problem as my subaru. It overheats with the thermostat, but there are no bubbles in the radiator when idling, only when you rev the engine wich I guess is normal. There is no heat from the heater core as well. Do you think it could be a blown head gasket as well?
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Monday, November 24th, 2008 AT 8:41 AM
Tiny
JAMES W.
  • MECHANIC
  • 2,394 POSTS
Yes, we can't rule out headgasket on the '91 Blazer, but I'm always hesitant to blame this first. You can check coolant entering a cylinder(s) by doing the same "overnight sit" test I described earlier. Usually you can tell by just pulling the plugs and looking for one or two that are loaded up or "rusty" in color.
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Monday, November 24th, 2008 AT 9:53 AM
Tiny
BABYCARLOS
  • MEMBER
  • 5 POSTS
I did some research on the 91 blazer and as I suspected earlier the thermostat was being inserted the wrong way. Since this car has a reverse rotation water pump the thermostat has to go upside down. I tried that and it worked like a charm. The car does not overheat any more and there is heat.
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Monday, November 24th, 2008 AT 9:52 PM
Tiny
JAMES W.
  • MECHANIC
  • 2,394 POSTS
Good man! I knew you'd figure it out. We can usually tell a person's mechanical ability by how they word their posting.
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Tuesday, November 25th, 2008 AT 2:16 PM

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