GMC 454 Oil Leak Question (almost Mustang related)

Discussion in 'Classic Mustang Specific Tech' started by Platonic Solid, Sep 22, 2006.

  1. Yeah, I know this isn’t a Mustang question, but considering this is an engine oil leak issue, I’m sure it’s applicable to most engines.

    My 89 GMC pick-up, with 137,000 miles on it, has been leaking oil for a few years, though I’ve never been able to figure out where the leak is. I only put a few 1000 miles on it a year, so it wasn’t a big deal. I just check it every time I use it. A few weeks ago on the highway, on my way to Mustangs Unlimited to pick up new fenders, the serpentine belt slipped off the tensioner pulley. (Apparently NAPA lists the same pulley for the tensioner and the idler which I now know to be wrong. :bang: ) Not wanting to get stuck on the highway, I drove it for a few minutes to get off the exit and close to a phone. The coolant was bubbling out of the overflow tank as I stopped in the parking lot of the local fire station.

    I had it towed home. Replaced the whole tensioner assembly this time, since that was the only way I could get the correct pulley. Changed the oil, filter, and coolant. No sings of coolant in the oil, nor oil in the coolant. It starts and runs like a champ, with a little more valve chatter than it had previously. Though I think overheating has caused the oil leak to get worse – at least I can now see where it’s coming from (sort of).

    I saw smoke coming from around the exhaust manifold near the front right cylinder so I cleaned the area with some carb cleaner and took a closer look. The oil is visibly coming out, at that one cylinder, between the exhaust manifold and the head. It must be a pretty bad leak since I can see it ooze upward onto the head from the top of the exhaust manifold as soon as the engine is started. I’m sure new oil is helping the situation.

    I could do a compression test, but am wondering if I wouldn’t just be wasting my time. I’m thinking it’s probably time to buy a rebuilt long block. What do you guys think?

  2. Most auto shops can put a dye in the oil, after running it a while, a black light can be used to determine where the leak is coming from
  3. Cool idea! Though that doesn't say much about the shop I've been going to, since I asked them to try to locate the leak about a year ago and they gave up.

    I got a price for a rebuilt long block from PowerPro for $2,200. The mechanic quoted $1,000 for the install. I haven't made any commitments yet.
  4. A new engine at 137k? I know it a Chevy, but you should be able to get more out of it than that unless you really did hurt something with the overheating. I think the oil coming from "between" the header and the head is just a leaky valve cover gasket. Do a compression and/or leakdown test and see where it stands at that point.
  5. I wish it was just a leaky valve cover gasket, but they were replaced about a year ago in hopes that it would solve the problem. Also, after cleaning the area with carb cleaner and running the engine, I can clearly see the oil traveling up from the exhaust manifold seam onto the head while the area just below the valve cover at that cylinder remains clean. Thus, I'm assuming this means the oil must be leaking into the cylinder via the head or the piston rings.

    Edit: I guess maybe it's time to break down and buy a leakdown tester.
  6. I would think that most reputable shops would be able to do that check. I've even had a shop do it in my AC because the leak was so small and gradual, they could not determine the source of the leak without the dye.
  7. Well, does it smoke? If the oil was passing through the exhaust port then and somehow between the manifold and head, you would definitely be getting exhaust smoke.
  8. Hmm, good point. Yes, it smokes. The way oil smokes when you spill it on a hot engine. Not like exhaust smoke under pressure though. I'll take a look at it again afterwork tonight.

    It seems to me, considering how quickly after starting the oil appears, it almost has to be coming from the exhaust valve guide.
  9. OK, I took a few shots of the offending area:

    First cleaned:

    After running 5 min.:

    After running 10 min.:

    Attached Files:

  10. Hi Platonic Solid, I am looking at buying an older Class A Winnibago 454 with the exact same problem on the passenger side, rear cylinder. The oil weeps out the seam, and smokes when the engine warms up. I'd be interested if anyone knows what the actual problem is, because repairs on these engines can add up real fast. Thanks !
  11. Eight years later....
  12. Yes Mr. Clone, 8 years later. My, you can count. And you have time to respond, with nothing helpful. I asked myself, what kind of person trolls these blogs with nothing better to do. Ahh yes, a clone driving poser. Time you retired "Founding Member". :(
  13. good luck with that pal. Why dont you just PM him instead of bringing up a old post that doesnt have anything to do with classic mustangs.