Hypothetically, if you had a slow gear oil leak, what would happen over time? | FerrariChat

Hypothetically, if you had a slow gear oil leak, what would happen over time?

Discussion in 'Technical Q&A' started by Mike328, Feb 26, 2004.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. Mike328

    Mike328 F1 Rookie
    Rossa Subscribed

    Oct 19, 2002
    Boulder, CO
    Full Name:
    Let's say you have a car like our 308/328s with a gear oil leak somewhere, leaking a little bit each time you drove the car.

    Gradually, the gear oil level gets lower. As the gear oil continued to get lower, what would the symptoms be, and what would the consequences be?

    Given a leak of dark fluid on the garage floor (not brake fluid), what's an easy way to tell if it's motor oil vs. gear oil?
  2. TOM B

    TOM B Formula 3

    Jul 24, 2003
    Orange County, NY
    Full Name:
    Thomas Buckley

    The easiest way to identify mysterious automotive fluids is by taste and smell. Most gear oils smell like baby vomit. When burned, the smell is bad enough to turn your stomach.

  3. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    Full Name:
    On which oil, they smell different. Also, as you know, gear oil is thicker.
    I am assuming you check engine oil level fairly often, so even if there is a leak, you'd top it up and outside of the mess (and risks) caused by leaking fluids, no harm done.

    Gear oil is a bit harder. How often do you change? I do mine annually and check it mid-season (I track the car). Unless you have rampant leakage it shouldn't be too much of an issue.

    One corollary: if the shift shaft seal is going between the engine and the box, I assume the gearbox will tend to overfill (flow from thin oil side to thick oil side, as it were) and under pressure will vent out the case (again, messy but not disasterous). If it flows the other way (gearbox to engine) - anyone know? - the gear box would progressively receive less oil and I presume more wear/noise/diff chatter will result.

    For me, the source of the leaks on the lower part of the motor/gearbox have been:
    - transfer case seal (I re-sealed mine)
    - engine mount studs (ditto)
    - shift shaft seals (not a big issue for me to date)
    - engine pan nuts (I talked to Norwood's and put on Stat-O-Seals)
    - diff seals (replaced)
    - drain plug crush washers (replaced)
    - seal on clutch shaft inner (sorry, don't have the book to hand and my language is imprecise - not a big issue to date)
    - seal on speedo sensor (replaced)

  4. Husker

    Husker F1 World Champ

    Dec 31, 2003
    western hemisphere
    When you run out of gearbox fluid, all of the sudden you will notice that you hear a sort of "grinding" noise when driving the car. The car will sound more like one of those old Honda 70 or 90 trail bikes. Passersby may notice some smoke coming out from underneath your car that will alert you something's not quite OK. Depending on the wind direction, you should soon smell something fishy. Well, not fishy, but more like the smell of a soldering gun when in use. At this point you'll know something's not right more-than-likely. When you figure out that you've probably got something screwed up somewhere, don't worry - you're just screwed. Hope this helps.
  5. Dom

    Dom F1 Veteran
    Owner Rossa Subscribed

    Nov 5, 2002

    Do you know where the gear oil is coming from? Is it a possibility that it is venting from the breather cap? I had a leak coming from mine, and I discovered the breather cap vent line solution in the following thread:


    BTW, my car is filled with Swepco gear oil, which is green, so that's how I knew it was gear oil that was leaking.

  6. Gianluca

    Gianluca Formula Junior

    May 6, 2003
    Centreville, Virgini
    Full Name:
    Gianluca Chegai
    I have a question not directly related to this thread.

    I keep on hearing about leaky engine mount studs (see pma1010 post) but I just had my engine apart and the stud couldn't leak because there is no penetration into the transmission or oil pan case.
    Has anyone else noticed this?


    1981 308 GTSi
  7. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    A) my motor oil never gets beyond amber before its changed, so this one would be easy
    B) gear oils have sulfur to decrease gear tooth pressure under load, you can smell sulfur
    C) brake fluid will evaporate given a couple of days (my brake fluid does not get to amber yet alone dark)

    One strange consequence is that it might shift easier when cold into 2nd gear!

    But, realistically, when the oil drops to the point where the bearings are not being lubricated, you will hear a noise of such utter clarity that you will pull over and have the car towed rather than risk the rest of the associated parts. At this point, its too late. Unfortunately, at this point the gear teeth are still being lubricated so you don't hear the gear whine increase much.

Share This Page