440 question, will a rear main seal leak when the car is just sitting, not running?

[RockinRobert]

I am trying to track down a small leak in my 66 Belvedere II. Is the oil level high enough to leak out of the rear main seal when the car has been sitting in the garage for weeks? Or do they leak mainly when the motor is running? Before I took it out last weekend I noticed an oil spot under the car. It had been sitting in the garage unstarted for a couple months. Definitely drips around the rear edge of the pan. Just trying to figure out where to start looking. Going to wipe it all clean in the morning and see if it tells me anything.

 

[65-440]

Clean everything off and put some UV dye in the oil

 

[pnora]

No. Oil level will be lower than the seal. At least it should be unless it is overfilled. Rear mains leak when running. They can sling it in the bell and make it hard to find. Clean it well and keep an eye on it.

 

[1 Wild R/T]

Proper oil level is well below the rear main seal or the pan gasket... Only thing that continues to see oil is the pan itself... Valve covers might see a little oil but most should drain back into the pan...

 

[hemidon1]

Its VERY easy to replace the rear main seal in your 440--I do alot of them--to bad your in cali--just clean it up and leak check it--most of the time its the oil sending unit or valve cover gaskts--but the rear main in a 66 is possibly the source--look before you leap--

 

[Mick56]

If the rear main is bad, it will leak oil out onto the area around the back of the engine. When parked, the oil will drip onto the ground.

 

[super-bee_ski]

Yes
INMO, all rear Main seals will leak
The "other guys" are smarter than me, ....and know more
I simply do not have good luck...although managed to successfully "FLY" in a Air Force plane for 18 years and survive.
But,
The weight of the Crank settles, and causes a distortion on the seal, weight and distorion on the bottom and that is where a small but significant leak will develop
Again, everyone is smarter and more knowledgable than me but on some cars, mine leak until you drive them.

Just saying.

 

[dvw]

Plug the breather. Apply low pressure air through the pcv opening in the valve cover. Spray the motor with soap water. Watch for bubbles. This method is foolproof, cheap, and easy.
Doug

 

[BeepBeepRR]

Plug the breather. Apply low pressure air through the pcv opening in the valve cover. Spray the motor with soap water. Watch for bubbles. This method is foolproof, cheap, and easy.
Doug

The road runner has a perpetual valve cover leak on the passenger side... I bet if I tried this method it would look like an episode of Lawrence Welk's show.

 

[Dibbons]

Plug the breather. Apply low pressure air through the pcv opening in the valve cover. Spray the motor with soap water. Watch for bubbles. This method is foolproof, cheap, and easy.
Doug

I used hair dryer with the soapy water and found an oil pan gasket leak:

 

[4speed68rt]

Cool trick!

 

[GetX'd]

Most of you guys are Mopar smarter than me - but if there’s one thing I knew was the idiosyncrasies of the X. My rear main leaked small amounts for several years after a complete rebuild. The car would sit for lengthy periods and I had that small perpetual leak - yes from the rear main. That’s my 2 cents and no it wasn’t coming from somewhere else.

 

[1 Wild R/T]

Most of you guys are Mopar smarter than me - but if there’s one thing I knew was the idiosyncrasies of the X. My rear main leaked small amounts for several years after a complete rebuild. The car would sit for lengthy periods and I had that small perpetual leak - yes from the rear main. That’s my 2 cents and no it wasn’t coming from somewhere else.

No doubt rear mains do leak, pretty common.. But the oil level in the pan is lower than the seal... So if the engine hasn't run in weeks & it's still leaking as the original poster states than it's something other than the rear main seal...

If it leaked when parked & maybe a little dripped that had already gotten into the seal area when running but didn't drip till a day or two later sure... But weeks later something else is leaking...

 

[66Satellite47]

IMHO, the rear main seal only leaks when running, oil level should be well below the seal at rest, BUT the oil that does leak while running lingers in the bellhousing area to leak from there for a while. Valve cover gaskets are a likely source, use methods described above to locate those.

 

[Darter6]

all rear Main seals will leak

Old saying, "If it's a MOPAR it's gonna leak" .
I have not been happy with the replacement seals as they all seem to leak.Some soon,others after several months.
I took apart a 85 318, basically for a reseal and cleaning. Was surprised to see a rope rear main. Thought you know what ? I ain't changing it as it showed no sign of leaks.Took the chance and the engine rear main is still dry.
So I started looking for Mopar rope rear main seals.Kinda pricey at $40.Looked one up for a Ford, $5.
I may get the one for a Ford to compare but no plans for any engine work at this time.

 

[Challenger340]

Does the rear Main Seal leak when it's running ?

Run it and watch while parked.... because of it does ?
then it's bound to drop the Oil residues once parked.

And NO.... 440's can be built to run completely leak free.

 

[blue69runner]

Looks like everyone covered all the bases. The rear main seal is the worst problem with most motors. Take a weekend and put a new seal in and problem solved.

 

[Bob Sawyer]

Quick rear main seal story.
In 1979, my buddy and I drove his '69 Charger R/T from Princeton, WVA to Indianapolis for the Car Craft Magazine's Street Machine Nationals.
The day before we left home he had a local garage install a rear crank seal in the 440.
After about 30 miles into the journey the oil pressure started dropping. By then we were 2 quarts low. The underside of the car was covered with oil. We continued on to Indy and went through 22 quarts of oil. The last day there (Sunday morning), we jacked the car up & blocked it, removed the oil pan and discovered the lower half seal was installed backwards. Installed a new seal and headed home. Cleaning the undercarriage after all that oil was quite a job.

 

[Challenger340]

Looks like everyone covered all the bases. The rear main seal is the worst problem with most motors. Take a weekend and put a new seal in and problem solved.

Not always ?

We do this for a living.... so we are supposed to act like the professionals at this ? and we Dyno everything in front of the customer before it leaves....

just say'in here....
so pretty darn embarrassing if the rear Main 'leaks' while we're putting it through it's paces on the Dyno ?
And it doesn't matter if it's a $40K HEMI or a $8K resto style 440 Wedge... same thing.
So during engine assembly.....
we STOP with just the Crank installed before going any further, install the Oil Pan and fill with Oil... then HANG the Engine off it's front therein completely submerging the rear main in Oil !
Come back in a while, because if it's gonna leak you will find out right then ! You can even turn the Crank a few rotations and see if you can get it to leak ?
Then.....
If all Dry ?
remove Oil Pan and continue assembly
If leaking ?
remove Oil Pan, Crank and Seal and start over.

 

[R413]

Yes
INMO, all rear Main seals will leak
The "other guys" are smarter than me, ....and know more
I simply do not have good luck...although managed to successfully "FLY" in a Air Force plane for 18 years and survive.
But,
The weight of the Crank settles, and causes a distortion on the seal, weight and distorion on the bottom and that is where a small but significant leak will develop
Again, everyone is smarter and more knowledgable than me but on some cars, mine leak until you drive them.

Just saying.

This is false information. All rear main seals do not leak.

What is the main bearing clearance .0015-.003. So the crank settles max half of those numbers so .00075-.015. If you believe that “theory” which I do not.

When the engine is running the rods and pistons are pushing down on the crank and so it’s loaded in the down direction anyway. Then when it sits gravity will pull the crank down, but not any harder that the forces when the engine is running under power.

that Myth is busted