heavy black smoke during Idle 91 subaru legacy non turbo


Asked by Apr 01, 2015 at 02:24 PM about the Subaru Legacy

Question type: Maintenance & Repair

Just did my head gasket on 91 Subaru legacy all went well seemed like I solved the problem on a fair test run. 3rd day into it started getting heavy black smoke out tail pipe. Afraid to even start it now. Car seems to run ok even while such heavy smoke. There was an intermitittent clicking noise in motor during test runs. I put in some stp oil stuff which seemed rather think. In dollups it came out. Dunno. Hoping its something simple.

3 Answers


Does this have a distributer that can advance the timing, etc? Black smoke should be unburnt fuel and rather rich!! I doubt this would be carbon build up but I could be wrong. You've got some good details man, I hope someone comes along that can help. In the meantime, you might try asking around on the legacy or NASIOC forums. Post additional info/questions/fix for future help. I'll keep thinking ;)

1 out of 1 people think this is helpful.

thank you for your concern walth..no no distributer. I did start the car the other day and it was still real heavy. I decided to let the car idle for a few hours and see what happens. Smoke cleared up pretty good. Only thing I can explain is the abnormaly thick STP engine oil treatment I put in. I'm guessing it plopped and globed onto the rocker arm essembly straight from the bottle and just sat there. It took a while for it to burn off so to speak. Going to idle the vehicle again tomorrow for a while. If it is no longer heavy smoke upon start up I'll know I was right


any updates?

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