'91 305 burning oil

rustyroosterrustyrooster Member Posts: 2
edited March 2014 in Chevrolet
I'm thinking of buying a 1991 caprice with 305 TBI. It's only got 70,000 miles and it burns oil. What's the most likely source of this for these cars and how would I detect it ?

I know my 87 camaro 5.7 burned oil and it had fairly low mileage. I seem to recall that chevy had a problem with valve oil-seals. I never got around to replacing the oil seals before selling it.

If I check the compression, I could still get a high reading since the compression rings would be ok, but the oil ring(s) shot.

At least 1 plug is oil-fouled.


  • spokanespokane Member Posts: 514
    It depends on the price and what you expect of this car. An oil-fouled plug is usually an indication of need for expensive engine repairs.
  • rustyroosterrustyrooster Member Posts: 2
    Thanks Spokane. If the oil is coming from say a leaking intake, or valve seals, actually this is pretty cheap to fix (parts), though quite labourious. If the problem is in the rings, I think I'd pass on the car altogether. I was wondering if there was a known problem with these cars. I'm betting on valve seals, since the mileage is so low.

    Are there any other chevy discussion groups around ? I've been to gmforums.com, and searched the newsgroups. I can't believe there aren't more active discussion groups ... esp. more technical ones. Thanks.
  • jgmilbergjgmilberg Member Posts: 872
    It's probably the valve seals leaking, but I will be willing to bet that the valve guides are wasted too. That means a head re-con. It is a really involved repair, but it can be done. These motors for some reason also almost always develop an intake manifold coolant leak, so replacing/rebuilding the heads would take care of that too. Just remember there is no replacement for good gaskets, and you get what you pay for. Personally I use fel-pro perma-torque gaskets with the built in silicone sealant on the gaskets for water jackets.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    A compression test will fool you sometimes that is true but a cylinder leakdown should tell the story.

    Bad seals or guides would usually manifest symptoms like lots of smoke on cold start, but the smoke should diminish as the engine warms up--except for high vacuum situations.

    Bad rings usually cause blue smoke under all conditions, and you might even see blow-by if you remove the oil filler cap, as well as a grungey air filter as blow-by comes through the PCV valve.

    It would be good to do a leakdown, since you don't want to put new heads on an engine with a weak lower end anyway.
  • alcanalcan Member Posts: 2,550
    If the heads are already off it's easy to tell if the oil rings are pooched. The outer edge of the piston crowns will be clean, with no carbon for about 1/8" - 1/4" all around the perimeter. Oil leakage past the rings does a pretty good job of washing the piston crowns
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Oh, that's tricky. Thanks.
  • jgmilbergjgmilberg Member Posts: 872
    I have seen those scopes that you stick into the cylinder through the spark plug hole, I am sure if you had one of those you could see what alcan is talking about w/o head removal. It looks like a mini video camera set up, and if memory serves it runs around $250 for the thing.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Man, I'll pull his heads off for $250 and take a look for him!
  • swschradswschrad Member Posts: 2,171
    the idea is you get to use it ten times or more a year, and then the snooperscope is paid for and makes money for you afterwards. if you have that many rotmobiles with people who will choke out for a diagnostic but sound hesitant about spending any money on the car, it can be a good little tool, I would think.

    and they can't blame you for "wrecking my car by pulling the heads" with the gizmo if they are less than upfront moral citizens ;)
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Okay, you convinced me! I'm putting my sockets back in their tray.
  • swschradswschrad Member Posts: 2,171
    great, now, be sure to stay off the phone. when you need help with a diagnosis, the Psychic Friends Network will call.

    oh, wait, it's always the Psycho Fiends Network that calls me. never mind....
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    I never have trouble diagnosing problems, I just have trouble actually FIXING them.
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