Piston Slap: A Fireball of a 3.8L Oil Leak?

Sajeev Mehta
by Sajeev Mehta
piston slap a fireball of a 3 8l oil leak

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 3800pro.com 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 [s]LS4-FTW[/s] 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 sajeev@thetruthaboutcars.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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5 of 52 comments
  • 28-Cars-Later 28-Cars-Later on Dec 17, 2014

    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*.

  • Kmoney Kmoney on Dec 17, 2014

    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.

  • Indi500fan Indi500fan on Dec 17, 2014

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

  • 71 MKIV 71 MKIV on Dec 31, 2014

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