Gilroy AutoWorks

Auto Repair, Auto Parts, Oil Changes, Tires & Service You Can Trust

(408) 842-5500

  • About Us
    • Our Team
    • Videos
    • Did You Know?
  • Services
    • Oil Change
    • 52 Point Courtesy Inspection
    • Brake Check & Repair
    • GDI System Service
  • Auto Parts
  • Resources
  • Blog
  • Reviews
    • Yelp Not Currently Recommended Reviews
  • Contact
    • Privacy Policy
    • Terms & Conditions
    • Sitemap
You are here: Home / Tips / Diagnosing Oil Leaks Part 1 – Rear Main Seal

February 25, 2016

Diagnosing Oil Leaks Part 1 – Rear Main Seal

The rear main seal—or rear crankshaft seal—is the working seal against the rotating crankshaft where it exits the rear of the engine.  When a rear main seal leaks, engine oil will often be found dripping from between the engine and the transmission.  If your vehicle has a clutch…it may also slip or grab.  Replacing the rear main seal often requires removal of the transmission. Due to this labor intensive job, shops will often suggest having the rear main seal replaced anytime the transmission is removed.

Most rear main seal leaks occur due to a combination of normal wear in the crankshaft & seal…and the general process of drying, hardening and shrinking of the main seal over time.  The three types of rear main crankshaft seals in use today are: Rope or wick, neoprene or split, one-piece.  Each offers its own features and benefits…and their respective pros and cons.  Most older American engines originally used the rope or wick-style seal.

Motor oil protects more functions within an engine than any other component, fluid or material.

1st: Look for the Drip Source

The rear main seal is essentially hidden in a position that you won’t be able to slide under your car and view it directly.   You’ll probably need to go through a process of elimination before arriving at the conclusion that the seal is indeed the culprit. If you notice your oil level going down…but can’t see a noticeable drip when the car is parked…you may be experiencing the early stages of a leak  [Changing oil & filters regularly will increase your odds of catching the leak in it’s early stages.]  Start your vehicle and let it idle for 15 minutes.  That may help you identify a leak, or at least begin to show some oil leaking from the engine.

After determining you’ve got a visible dripping leak, it’s best to start looking for a source…working your way from the bottom and moving upward. If you see oil dripping on the back of your oil pan or on the front of your transmission bell housing it’s possible you have a rear main seal leak.  But don’t panic yet!  Continue the process of checking other options higher up that may be real source of the oil dripping down.

2nd: Check Valve Cover & Valley Pan Gaskets

Use a flash light to thoroughly inspect your valve cover gasket(s) and valley pan gasket for leaks.  If your diagnosis overlooks either of these as the actual drip source…it could cost someone a chunk of money…because either of these issues will be much less difficult to replace since they’re easier to get to.  That’s the leaky rear main seal’s biggest challenge: it requires major disassembly of your engine – so the labor is typically too much to do at home.  Skilled labor in a professional shop environment costs money…for sure.  But a DIY labor mistake at home that causes a complete engine overhaul and/or an accident…costs considerably more.

Read More

Article by admin / Tips / crankshaft, oil leaks, rear main seal

Where to Find Us:

Gilroy AutoWorks
250 Nagareda Dr #1
Gilroy, CA 95020
(408) 842-5500



Business Hours:

Mon - Thur
8:00am - 5:00pm

Friday
8:00am - 4:00pm

Sat:    Closed
Sun:   Closed



Latest Posts:

  • New Engine Tech to Disrupt EV Auto Market
  • 2023 GMC Hummer EV Pickup – News, Reviews & Muse
  • Toyota 4Runner TRD for 2023 – News, Reviews & Muse
  • Acura Integra for 2023 – News, Reviews & Muse
  • Delorean for 2023 – News, Reviews & Nostalgia
  • Windshield Cleaning Tips – Inside & Out
  • Toyota BZ4X for 2023 – News, Reviews & Muse
  • Pedestrian Safety for Teen Drivers

Latest Tweets

Cheapest Electric Cars - Most Affordable EVs for 2023 | Edmunds dlvr.it/SdGfdg @edmunds pic.twitter.com/2NRtOyEKQe

Yesterday from Arnold Tellez's Twitter · reply · retweet · favorite

2023 Jeep Compass Makes AWD and New Turbo Engine Standard dlvr.it/SdGCFB @roadshow pic.twitter.com/eInIHd8DAM

Yesterday from Arnold Tellez's Twitter · reply · retweet · favorite

Best Convertible Cars of 2022 - Expert Reviews and Rankings | Edmunds dlvr.it/SdCc1T @edmunds

About 2 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

2023 Honda Pilot Starts Around $40,000 dlvr.it/SdC6gT @roadshow pic.twitter.com/rneYIajFUb

About 2 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

Rivian Releases R1T Update to Prevent Unintended Shifts | Edmunds dlvr.it/Sd8RsV @edmunds pic.twitter.com/9oRuDrIlqE

About 3 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

2024 Kia Seltos Refresh Brings More Power, More Tech dlvr.it/Sd7zpn @roadshow pic.twitter.com/Tq5CJzgBMM

About 3 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

2024 Mazda CX-90: This Is Everything We Know dlvr.it/Sd5SnN @edmunds pic.twitter.com/IAUhP0GnDn

About 4 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

Best Tool Chest for 2022 dlvr.it/Sd24qT @roadshow pic.twitter.com/QsenrCtELN

About 5 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

2023 Ford Bronco Sport Gains Off-Road Cred With Black Diamond Package dlvr.it/Sd15rC @edmunds pic.twitter.com/pMj2HdwMYB

About 6 days ago from Arnold Tellez's Twitter · reply · retweet · favorite

Follow Us!

  • Facebook
  • Instagram
  • LinkedIn
  • RSS
  • Tumblr
  • Twitter
  • YouTube

Communities We Serve:

Gilroy –  San Martin – Morgan Hill – San Jose – Campbell – Los Gatos – Saratoga – Watsonville – Hollister – Santa Cruz – Prunedale – Castroville – Freedom – Cupertino – Milpitas – Mountain View