Help me find this oil leak please!

Discussion in 'Engine & Drivetrain' started by John03Z71, Sep 19, 2018.

  1. John03Z71

    John03Z71 TYF Newbie

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    I have a 2003 Tahoe 5.3L Z71. I've developed a very bad oil leak over the past several months. It started out as a moderate leak, having to add a quart every month or two, but recently has been leaving a couple softball size circles when parked and I have to add a quart every 5 days or so as the check oil level light comes on this fast... so I took it in to a reputable shop and they said it was my oil pan gasket. $400 later I'm out the door and drive home about 30 miles, park it, come out later that evening and see more large oil spots under the truck. Pissed.

    I called the shop and they said there was so much oil under there that they had to clean up (true story) that it was hard to tell exactly where it was all coming from, but the pan gasket was definitely leaking, as well as the oil cooler block off plate gasket (both replaced). He insisted that those were the two main culprits, and explained to me that since those were leaky and now sealed up, the increased "pressure" is likely causing oil to be forced out of other areas that were also leaking, but only slightly before the new pan gasket and block off plate gasket. This sounds logical, however part of me is thinking they just didn't take the time to properly diagnose and find all my leaks. In fact it's leaking worse now than when I brought it in and had the pan gasket and block off plate gasket done. He also mentioned my rear main seal is leaking as well as my timing cover gasket, but to just "keep an eye on them for now". Hard to "just keep an eye" on oil levels when I leave the shop and 5 days later the check oil level light comes on!

    Last Thursday the check oil level light came on, so I dumped a quart of oil in along with about 10oz of Bar's Stop Leak which was recommended by the shop. Fast forward to yesterday, on my lunch break I hopped in and am greeted with "check oil level" on the dash... I hopped out and took a peak underneath, and there is a steady drip coming down almost like a drippy faucet. I top it off and drive home, then I crawled under there last night and spent about 30 mins wiping / drying everything up real good because I wanted to pinpoint the leak. Once dry, I cranked it up and crawled under it with a flashlight right away. After about 15 seconds, the first sign of oil came down from the starter bolt on the side closest to the block. This quickly turned into the leaky faucet type leak, it was dripping a drop of oil at least every 2-3 seconds. After about a minute, it started running over to the other side of the bellhousing and dripping off one of those bolts, which then began dripping down the bellhousing area where the engine and transmission meet, creating what APPEARED to be a rear main seal leak. I popped off the inspection cover on the bellhousing (after shutting engine off) and it was dry as a bone, good sign right?

    I continued to let it run for about 5 minutes and the area above the starter appears to be the only origin of this horrible leak, again dripping constantly every couple seconds. It was late and I didn't have time to pull the starter, so my question is what is above the starter that could be causing this bad of a leak? I replaced the oil pressure sensor about 3-4 years ago, and also reached my finger way back there to check if it was wet and leaking down the engine to that area and while there was some grease around it, it did not feel terribly wet back there so I'm not convinced it is the culprit due to the significant volume of oil that is leaking out. I've heard the rear main is generally a slow leak, so since the flywheel is dry behind the inspection plate and there wasn't any oil leaking directly between the engine and transmission I'm hoping it's not the rear main.

    Sorry for the long post but I wanted to provide as much detail as possible. Any helpful info that would assist me in pinpointing this bad leak coming from above the starter would be much appreciated!
     
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  2. mattbta

    mattbta Full Access Member

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    Subscribing. I have a leak similar to this...seems to be coming down onto the starter. Already did oil pan gasket too.
     
  3. smcnair

    smcnair Member

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    Valve cover gasket?
     
  4. John03Z71

    John03Z71 TYF Newbie

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    I did the valve cover gaskets about 3 years ago, checked them last night and there is a small bit of "grease" around one area but certainly nothing wet to this degree.
     
  5. Bigbertha78

    Bigbertha78 Full Access Member

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    Remove your starter and look above it, that is the crankshaft position sensor, may possibly be leaking from there, it has a small O-ring that seals it. Also, check behind the intake with a mirror and glance at the valley pan gasket or the oil pressure sensor, may be leaking enough to trail down the back of the block.
     
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  6. John03Z71

    John03Z71 TYF Newbie

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    Thanks. I'm picking up the crankshaft position sensor and also a camshaft sensor today, hopefully one of the two will be the culprit...
     
  7. swathdiver

    swathdiver Full Access Member

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  8. bottomline2000

    bottomline2000 Full Access Member

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    Its your oil pressure sending unit. It's at the back of the intake in the middle. It can be reached with a short extension, swivel and socket. No need to remove the intake. They make a special magnetic socket just for this. I would torque it to spec since it has a crush sleeve on it..

    They can develop a leak internally and oil come straight thru it so tightening it will not help if the internal seal is compromised.

    The shop should have started at the highest point of the leak not the lowest..lol..

    Sent from my SAMSUNG-SM-T377A using Tapatalk
     
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  9. Scottydoggs

    Scottydoggs Full Access Member

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    i agree. oil pressure senders leak like your pouring oil out a maple syrup bottle. rev the engine up and build up oil pressure and it leaks even faster.
     
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  10. John03Z71

    John03Z71 TYF Newbie

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    Thanks. I did replace the oil pressure sending unit about 3-4 years ago, is it common for them to fail again like this? When I replaced it before it was due to the gauge reading way too high pressure, no leaking.

    Also I reached my hand way back there last night and felt all around but didn’t feel any wet oil, just some dried up crud was on my finger. Any other good way to check this from another angle, or what is directly below it that I would see it dropping down from? I feel like I inspected everywhere from the top down last night and the bad leak started right at the starter bolt, couldn’t see any trails above it.
     

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