By on December 17, 2014

v6 engine. Shutterstock user Rost9

Robert writes:

I have changed the seal 2 times on my 3.8L Chevy and it still will leak. I had a place on harmonic balancer.I put the recommended slave to repair.It was not long enough to cover the bad spot on the balancer.It was close but they seal was damaged.They offer a different one that is $30+.This all occurred just out of the blue.I rebuilt the engine and it has 30,000 on it.I was wondering if there is something causing pressure around this seal.Pressure check on cylinders was good.Any ideas what to do or pressure is good too good.

Thank you sincerely – Robert

Sajeev answers:

The problem seems common, a leak behind the harmonic balancer at the crankshaft’s front seal.  Or maybe I misread your letter, or googled incorrectly.

I also presume you installed this “sleeve” to repair it, but it didn’t work because it was too short. The correct one, or perhaps General Motors makes a revised seal/harmonic balancer that supersedes your part number should solve the problem.  But the real problem?

I can’t find a clear solution. This thread on mentions blow by: excessive crankcase pressure that exacerbates an oil leak. You could bypass the PCV with a crankcase breather filter (if it won’t trigger a check engine light), then clean the motor and check for leaks…

…or install LS4-FTW the “different one that is $30+” as that might be the permanent solution.

Help us out, Best and Brightest.

[Image: Shutterstock user Rost9]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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52 Comments on “Piston Slap: A Fireball of a 3.8L Oil Leak?...”

  • avatar

    Has a Leak Down Test been performed ? .

    As I work almost entirely on older rigs , I find that many good running engines have excessive crank case pressure , usually because of piston blow – by but sometimes because of wobbly valve guides .

    Piston blow by is why I’m so fond of ‘ gapless ‘ piston rings and why I always do the 60 second breakin regime .

    Speedy Sleeves work well if there’s *any* wear on the damper’s machined sealing surface .


  • avatar

    Let’s see – stuck PCV valve, a kinked hose (or clog) in the PCV path, a clogged PCV intake breather (used to be in the oil filler cap; don’t know where they hide this nowadays).

    Or: (really bad news) Worn piston rings allowing excess blow-by that the PCV system can’t take up.

  • avatar

    Clogged PCV?

  • avatar

    A bit lost in translation…….

    Traditional Chevy small blocks (and big blocks) have fairly durable front seals but they slowly wear out and by about 100,000 miles or so they need to be replaced. I don’t know much about their 3.8 V6 motor but I do think it odd that the crankshaft would need a sleeve unless it has uber mileage.

    I think I would look closely at the balancer and see if the inner and outer are starting to separate which causes all kinds of issues. And those issues occur sometimes before the problem with the balancer is visual, at least while it is installed on the motor. I’d pull the balancer and give it a really good eyeballing specifically looking for a shift or separation that could cause a wobble and excessive wear.

    Another, last moment thought…is it the proper balancer as in was the original balancer swapped with a replacement that is not the correct one? Back to the small block/big block example, there are different balancers for different engines that will physically interchange but aren’t the correct ones.

    As for the thought about the clogged PCV that some posters have referenced, my experience with that problem (and I have encountered it) is that the back up builds up and causes oil to be forced up through the breather tube and back into the air cleaner/air box. You’ll know it, the element will be saturated with oil.

  • avatar

    One can always tell who has/had GM vehicles at their house by the abundance of oil stains on their driveways & garage floors.

    I realize some may claim this is trolling, but as I began to read this article I tried to think of a single person I know who has or had a GM vehicle having 50,000+ miles on it that didn’t experience oil leaks, and I can’t.

    Even the small block V8s and the venerable 3800, which even I will concede are durable, reliable motors (for the most part, on a relative basis), leak oil.

    • 0 avatar

      I’ve had plenty of refridgerator white, V6, long bed, rubber floor, 2WD Silverados over the years that didn’t leak oil.

      I cannot say the same for anything with the 3100 or 3400 in it.

      • 0 avatar

        “Recent model General Motors engines have more than their share of oil leaks. The Generation III and IV V-8 engines are notorious for oil spots. A little known technical service bulletin sheds some light on one issue.

        Rear main seal cover plate leaks

        Not only are the oil-leaks a nuisance, leaking oil sometimes damages the rubber suspension components. The 5.3, 5.7, 6.0, 6.2 and 7.0 liter GM engines often leak at the rear main seal area. Technically the seal itself is usually not the culprit. General Motors uses a cover plate, on the rear of the engine, in which they mount the seal.

        Defective castings of engine blocks and these covers, often result in major oil leaks. From 2004 through 2011, many of these engines left the factory with casting pits in the area where the rear cover attaches. The gasket can usually seal the oil, at least through the warranty period.”

        • 0 avatar

          I’m not doubting your claims. I am just saying that with V6 Chevy trucks, I’ve never had a leak. I’ve never purchased a V8 Chevy truck, just 10-15 V6 models. Part of that is that I would never have a Chevy as my personal truck. Always Dodge/Ram or Ford.

        • 0 avatar

          Also, the GM 4.3, 3.4, 3.5, Northstars, Shortstars, all quad fours, ecotecs, etc.- all leak.

          • 0 avatar

            They don’t particularly leak oil any more than any other makes. Northstars sometimes leak oil from the bed plate where it seals against the bock which is a PITA to fix, but I can name engines from other makes that do the same with about as much frequency.

            Where GM engines do excel is coolant leaks, however. The plastic coolant elbows on the front of the 3800 motors crack and leak, as do the plastic intake manifold gaskets.

            With the Northstar, without the addition of the little sealant pucks in the cooling system, coolant can literally weep from the pores in the block.

            The 3100/3400 of course leak coolant from the intake gaskets into the crankcase.

          • 0 avatar

            DAMN YOU LIM GASKETS!!!

          • 0 avatar

            Indeed. The finally smartened up with the later value 60* engines (3500, 3900) and made their intakes a dry design. Those motors tend to see some decent service life.

          • 0 avatar

            If you replace the gaskets the 3100 and 3400 you can get good life out of them. My sister’s Alero has been great since the replacement was done. When she goes the to Peace Corps after finishing her Master’s Degree in 2016, I’ll buy it from her and use it as my winter beater.

          • 0 avatar
            Felix Hoenikker

            2.2L 2004 Ecotec with 250K miles. No oil leaks.

          • 0 avatar

            Danio – I will concede your point, unconditionally, that GM engines tend to leak more coolant than oil. ;-)

          • 0 avatar

            The 4.0 V6 from the Frontier/Pathfinder seems to leak oil commonly.

            I had not heard big complaints about leaks from the 4.3 Vortec as used in all Blazer models.

          • 0 avatar

            I’ve had 4 that didn’t, ever.

            ’82 K-5 Blazer, 305.
            ’86 Camaro Iroc-Z, 305.
            ’88 S10 Blazer, 4.3
            ’00 Sierra 5.3.

            That’s every GM vehicle I’ve owned since I stupidly sold my ’79 Trans Am that did leak, slightly, but not at all badly, compared to my ’77 Power Wagon that leaked oil from the front seal, valve covers, and intake manifold. It also oozed coolant from the intake manifold. If only leaks had been it’s real problem areas, I wouldn’t have been so happy to see it go away.

      • 0 avatar

        ” One can always tell who has/had GM vehicles at their house by the abundance of oil stains on their driveways & garage floors.”

        Fair enough but , careful maintenance and repair can usually cork ’em back up ~ my old truck burned so much oil it fouled the spark plugs every two weeks so I replaced all the exterior cover gaskets using Permatex ‘ The Right Stuff ‘ on both sides of every one and presto ! no more oil drips .

        Making sure all those little rubber PCV etc. grommets are in good shape helps a lot too .

        I even learned how to make Air Cooled VW’s not drip .


    • 0 avatar

      Have had three Chevy’s and an Olds 88, never leaked a drop. Currently have a 2008 Malibu with 2.4 with 100K and no issues.

    • 0 avatar

      You know the pope is not going to like all of this trash talk on the anointed motor when he arrives…

    • 0 avatar

      I owned a 1995 C1500 with the 350 for 11 years. No problems ever with the engine leaks or otherwise. On of my top 3 vehicles I’ve owned. Of course I eventually had to replace, the starter, exhaust, alternator, water pump all before 86,000 miles.

    • 0 avatar

      I had a Blazer in high school with the 4.3l. After I got rid of it, I think the oil stain left on the driveway was the reason my dad finally had it refinished

      • 0 avatar

        My 94 Chevy Silverado 350 V8 leaked a little oil after 100,000 miles, but had a coolant weep at the interface of the intake and heads at very low miles. That original engine was replaced with a new GM crate 350 that so far, at 30,000 miles, is leak-free of oil and coolant. My wife’s Safari van with the 4.3 leaks large amounts of oil from the pan gasket during cold weather. In the hot summer, the leak all but vanishes. I know it needs a new gasket, but the shop wants a lot of money and the shop manual makes it sound like a pain to replace.

    • 0 avatar

      2002 Vue that did not leak oil. Having said that it leaked computers, clutches, transmissions and other expensive items. I would have really really preferred an oil leak.

    • 0 avatar

      2000 Impala 171K miles with 3800 no oil leaks. 2002 Intrigue with Shortstar 3.5 and 152K miles. No oils leaks. 2008 Impala 3900 V6 with 120K miles. No oil leaks. Current 2013 Impala with Global 3.6. Surprise! No oil leaks. 1996 Caprice Classic Summer driver with 4.3 V8 and 88K miles- no oil leaks whatsoever!

      My best friend in comparison- 2002 Ford Taurus 3.0 Duratec oil leaking all over the engine from intake and currently has antifreeze exiting the exhaust with less than 150K miles on the clock. 2008 Honda Odyssey with 102K miles is leaking transmission fluid from a cooling line.

      Colleague at work has a 2004 F-150 with a leaky 4.2 V6 that leaves oil spots every time he parks it.

      Close friend of 20 years has a 2008 Subaru Forester with 78K miles that this Summer blew out it’s rear main seal leaving oil everywhere on his new driveway. The dealer pulled the boxer motor to repair the rear main leak and also found both heads were leaking as well. 2500 bucks later and a very disgruntled owner to say the least!

      Summary- saying that only GM’s leak things on driveways is totally silly.

      • 0 avatar

        Yeah those Duratecs are notorious oil leakers, often from the bedplate.

        “1996 Caprice Classic Summer driver with 4.3 V8 and 88K miles- no oil leaks whatsoever!”

        Nice, I have one of these too. I was working on it over the weekend. It’s getting an LT1 with LE2 heads and a Comp XFI 292 cam. Gonna keep it on the stock aluminum faux wire rims with Mickey Thompsons. This is the sh1t I do with my free time.

  • avatar

    This time of year it seems like I’ve got a UPS or FedEx truck in the (concrete) driveway darn near every day.
    And all of those guys seem to be leaking. I’ve got black diesel oil spots all over the place.
    No snow to cover them up…so far.

  • avatar

    I had a 2000 Firebird convertible with the 3800 motor. It leaked oil. The dealer I bought it from changed the oil pan gasket. It still leaked oil. When the engine was cold, it would leak oil. If the engine was warm it leaked less oil.

    My mechanic pulled the tranny, and changed the rear main seal. In fairness, he tried to talk me out of it. I was told, that GM used a slightly different block on the RWD configuration, than was used on the FWD. They all had rear seal issues. Anyway after the fix, it still leaked oil. A can of Lucas seal treatment,and it leaked a little less oil.

    The 3800 In an F body, had the goofiest motor mount set up imaginable. Hard acceleration or a rough bit of road, and it could shear an aircraft quality motor mount bolt in half?

    Sajeev…Did a “Piston Slap” article about my motor mount. The consenses from the B&B was that in an earlier time, the Firebird had been hit, and hit hard. I found out too late that the registration had been done in Quebec, and then re done in Ontario. The Firebird went down in my personal automotive history book, as a fail !

    I always liked the 4th gen F body. However today I use one of those sheared aircraft quality bolts as a paper weight, it sts right here on my computer desk. It never hurts to be reminded of past mistakes.

  • avatar

    Sajeev – While generally LSx is always the answer, transverse LS4 likes to chew through torque converters if I am not mistaken. So in this case, it may not actually be the answer *gasp*.

  • avatar

    You say you rebuilt the motor. When reassembled, was the oil slinger installed on the crankshaft behind the timing cover. If not, it’s likely just the volume of oil overwhelming the seal. Seems silly, but I’ve seen this happen more than once… albeit never on a 3800 series.

  • avatar

    Cummins 6BT series, likely with X00,000 miles.

  • avatar
    71 MKIV

    in all my cars an oil leak means there’s still some in there. I worry when it stops.

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