Running the engine consistently with a low oil level can make the seal too hot or dry it out so that it warps and starts leaking. Driving with an overheated engine may have the same result. Adding too much fluid can "blow out" a seal, especially on a transmission.

Seals are rather fragile and easily ruined by a ham-handed mechanic. It is essential to mount seals flush in the recess made for it and for it to be free of dirt or burrs. It's easy to destroy a seal by an errant slip of a tool when working on something else. A gouged, dirty or dented seal will probably leak.

Improper installation or removal of a seal might damage the seal "seat," causing the new seal to leak after installation. Use the proper seal puller and installation tools for any operation involving seal replacement.

A guide to why your oil seal / Rotary Shaft Seal may fail

The below Oil Seal Failure Checklist provides information about seals leakage to those involved in the application and maintenance of Rotary Shaft Seals. Identifying and correcting the cause of leakage will assist the trouble-free, efficient and extended operation.

There are two parts an Oil Seal / Rotary Shaft Seal where leakage can occur:

• The interface between housing bore and seal O.D
• Between the seal lip and shaft

The following Oil Seal Failure Checklist shows the causes of failure and the means of prevention. A poster version can be downloaded here

SYMPTOM: Oil Seal rotates with shaft
CAUSE: Seal O.D smaller than bore I.D
RECOMMENDED ACTION: Select correct size seal and replace

SYMPTOM: Oil Seal moves in axial direction along the shaft
CAUSE: Seal O.D smaller than bore I.D and caused by the rotating of shaft or the internal pressure
RECOMMENDED ACTION: Select correct size seal and replace

SYMPTOM: Seal installed in declining condition
CAUSE: The I.D of housing bore is undersized, incorrect means of installation causing the seal to be misaligned
RECOMMENDED ACTION: Ensure housing bore is correct size

SYMPTOM: The deformation of the metal case
CAUSE: Use of incorrect tool to install the seal
RECOMMENDED ACTION: Use correct installation tool

SYMPTOM: The damage on the case O.D
CAUSE: The finish of housing is not correct and / or incorrect means of installation
Dirt adhering to the seal O.D or the housing I.D
RECOMMENDED ACTION: Ensuring housing size is correct
Use correct installation tool

SYMPTOM: Lip worn seriously
CAUSE: Insufficient lubrication
Application design restricts lubricant access to seal lip
RECOMMENDED ACTION: Ensure sufficient lubricant
Change design to ensure seal lip is accessible to lubricant

SYMPTOM: Lip worn seriously
CAUSE: Inner pressure too high
RECOMMENDED ACTION: Change seal design to pressure type

SYMPTOM: Lip partially worn
CAUSE: Seal partially installed
T.I.R of I.D and O.D are too big
RECOMMENDED ACTION: Select seal which T.I.R is suitable

SYMPTOM: Lip partially worn
CAUSE: Seal misaligned in housing
RECOMMENDED ACTION: Ensure housing bore is correct
Use correct installation tool

SYMPTOM: Lip hardened worn and cracked
CAUSE: High temperature / shaft rotation speed / pressure
RECOMMENDED ACTION: Select a suitable compound type
Supply sufficient lubricant

SYMPTOM: Lip material swollen
CAUSE: Incorrect compound selection
RECOMMENDED ACTION: Select the correct compound

SYMPTOM: Lip scratched
CAUSE: The shaft surface is not smooth
Scratch caused by incorrect installation tool
RECOMMENDED ACTION: Let all the lip configuration clear Install seal correctly

SYMPTOM: Lip turning out
CAUSE: Incorrect installation
Inner pressure too high
RECOMMENDED ACTION: Lubricate the lip and shaft before installation
Use pressure type seal

SYMPTOM: Crack on the base of flex section
CAUSE: Inner pressure too high
Sudden pressure strike on the flex section
RECOMMENDED ACTION: Use high-pressure type seals

SYMPTOM: Spring dislodged from spring groove
CAUSE: Shaft chamfer is incorrect
Incorrect installation
The retainer lip is too short
RECOMMENDED ACTION: Finish the shaft chamfer and lubricate the shaft before installation
Be careful while installing
Change the seal design

(Oil-Seals-Failure-Checklist-Poster.pdf)

M Barnwell Service is one of the UK’s most trusted Manufacturer, Stockist and Distributor of Oil Seals / Rotary Shaft Seals. For more information about our range and to talk to an expert contact the team today.

Require more learning? Below are some useful links:

Oil Leak Causes and How To Fix Them

Yes, it’s easier just to ignore the small puddle of oil forming under your car. Or pretend that the burnt oil smell is not coming from your engine. And is that blue smoke coming out of your tailpipe?

Oil leaks are something you cannot afford to ignore. It doesn’t always take a trained mechanic to figure out what causes engine oil leaks. A little hunting can reveal a lot, just don’t put it off or it can cause damage to your engine.

Is your car leaking oil? Fix it today with No Leak.

Leaks left unchecked can get on rubber hoses or seals and cause them to degrade prematurely. Leaking oil can cause ugly stains on your driveway and are an environmental hazard. And worst of all, engine oil leaks are a fire risk in your engine compartment and can result in catastrophic engine failure at the worst possible time, not that there is a good time for catastrophic engine failure. So fixing oil leaks should be your number one priority.

To check for engine oil leaks keep a close eye on your oil dipstick. If the level drops over time you’re losing oil. While driving, check and see if blue smoke is coming from the tailpipe. Blue smoke means oil might be leaking into the engine itself. After a drive, take a sniff to smell for burning oil. This could mean oil is leaking onto hot components of the engine itself. Lastly, check for the classic oil stains or puddles under the engine compartment, especially after it’s been sitting overnight.

Should you find a puddle under the engine, look a little closer. If the liquid is red it’s probably transmission fluid. If the liquid is green or orange and has a sweet smell, coolant is the culprit. Brown fluid will indicate an engine oil leak.

So what causes engine oil leaks?

We’re glad you asked. The vast majority of leaks are due to degraded engine gaskets, oil pan leaks, oil seals or bad connections. Crawl under the car and check the oil pan seals. While you’re there also check the oil pan drain plug. Next check the timing cover seal and the valve cover gaskets. Problems here can require extensive repairs that are not cheap. Don’t panic! You can always try fixing oil leaks yourself first. It’s not hard. Here are a few options.

Oil Leak Repairs At Home

The most cost-effective and easiest place to start fixing oil leaks yourself is by using a stop leak additive such as No Leak Engine Oil Stop Leak. Once No Leak is inside your vehicle, No Leak softens and conditions rubber seals to stop and prevent automotive leaks safely. It’s best used when engine oil leaks are first detected but is still effective on leaks that have been there awhile.

The next solution is to grab a torque wrench and check for loose bolts starting with the oil pan. Bolts can loosen over time. When the oil pan seems snug, move to the timing belt cover then the valve covers. Just note that each car model requires you to tighten bolts in a specific pattern and to a certain tolerance. Most auto parts stores can provide you with these specifications.

A leak of any kind should be addressed immediately, but an engine oil leak even more so. Knowing what causes engine oil leaks will help you know where to look and how to start fixing it yourself. Don’t ignore it, or hope it fixes itself. Be proactive. Protect and preserve your vehicle’s performance so you can keep it on the road where it’s meant to be.