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Old 4 Days Ago
Tboy's Avatar
Tboy Tboy is offline
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Join Date: Jun 2003                                                
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My Saabs: 94 900SE V6, 2000 9-5 Aero mt
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Default Rule out Headgasket Failure *Help me fix a Honda*

Posting this on Saabcentral cause I trust most of you guys, and I don't normally post to honda forums.

  • Helping a cousin repair her Civic with 221k miles so she can sell to a needy friend
  • She said "i can't keep coolant in it" and it "visibly overheats"
  • Two mechanics have told her headgasket.
This is where it gets interesting.I took the car and it would not overheat on me one day while driving through the neighborhood. Heat worked, everything normal. I try again another day and now the heat is not working and it overheats like a bad thermostat. So I removed thermostat and found the gasket buggered. This could have been the source of a leak. It was installed upside down with the bleed hole in the wrong spot. Tested the thermostat on the stove and it seemed to work fine, but cut the sprint out and put it back in fixing the gasket for more testing. Car no longer overheats (but does reach operating temp eventually) and can't see exhaust in the coolant, and don't see leaks anywhere. Oil looks clean.

I want to 100% rule out a headgasket before handing it over. I have a new thermostat in and am currently fixing other things that make it undriveable (like stuck brake caliper and ball joints).

  • Can anyone recommend a test or several where I can get a really good confidence level that the headgasket is intact without driving it? (runs and idles fine in the garage).
  • I'm worried that the failure might be so slight that over time the engine pushes out the coolant and then it overheats...
Advice appreciated!
1994 NG900 V6 >
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2000 9-5 Aero mt
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Old 4 Days Ago
02Pilot 02Pilot is offline
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Join Date: May 2019                                                
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There's a chemical test for exhaust gases in the coolant, which would be definitive. Failing that, you can pressure test the cooling system to 15psi - if it holds and no leaks appear (boroscope the cylinders) you should be good to go.
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Old 4 Days Ago
Saabohème Saabohème is offline
Join Date: May 2004                                                
Location: Columbus, Ohio
My Saabs: 2008 9-3 SS 2.0 6Spd JZW Stage 1
Posts: 11,145

Concur - but the chemical test only works where the HG leak allows communication between the coolant passages and oil galleys. If, for example, the leak is directly into a cylinder, no coolant mixes with oil to contaminate the two. When the HG went on my '95 vert, this was the case and the chemical test was a false negative. The leak down test conclusively proved the HG leak and is therefore, imo, the definitive test.
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Old 3 Days Ago
jvanabra jvanabra is offline
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1. Compression test
2. Leakdown test
3. Cooling system test
4. Block test (exhaust gas test)
5. Oil analysis

I think that's all the tests!
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Old 1 Day Ago
KaMiKaZi_t0M's Avatar
KaMiKaZi_t0M KaMiKaZi_t0M is offline
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Join Date: Nov 2007                                                
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My Saabs: 92 C900T vert, 95 9K Stg3+, NG900 HX35
Posts: 2,850

Cooling system pressure tests can definitely help if the cooling jacket portion of the gasket failed into the fire ring. Pressure test, leave it for 30 mins or so, and start the car. If starts hard and blows some smoke either a cracked cooling jacket or headgasket.
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