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Rear Main Seal Leak Or Just The Oil Pan Gasket?


BobMarls

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Got a significant oil leak... leaves a small pond on the ground after the car has been driven.
It appears to be dripping from between the engine and transmission.

 

Checked the transmission fluid level, it's full and the leaking fluid doesn't smell like gear oil.

Double checked the distributor housing and no oil there.

 

Changed the oil, didn't start the car and there was a small amount of oil that dripped out over night.

 

Pulled the inspection cover and there's no oil on the fly wheel.
If the rear main seal was leaking would I see oil on the fly wheel?
Is the oil level in the pan at or slightly higher than the gasket position, assuming there's the correct amount of oil in the car?
 

 

Thanks in advance for any advice :)

 

20140720_111226_zps40004600.jpg

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That's a hard one to answer definitively without your car here to stick my head under.

 

But:  the oil pan gasket's a lot easier to change than the main seal, so do that sixth.

 

First, change the o- ring on your distributor- I had one split once, and it dumped a lot of

oil down the back of the block.  Looked a lot like a main seal.

 

Second, check the rear seals on the distributor housing.  There's an m6 bolt that goes

into the left rocker tube, and that needs a special rubber sealing washer.  It leaks without it.

 

Third, check your valve cover gasket.  A chunk out of it in back will dribble, too.

 

Fourth, check your oil pressure sender.  They split, seep, leak, ooze, and can generally make a mess.

 

Fifth, make sure it's not coming out of one of the studs on the exhaust manifold.  It probably isn't, but it never hurts to check.

 

sixth, try the oil pan gasket.

 

Seventh, now, you're down to the rear main seal...

 

I'm sure there are a couple I'm missing, but that's most of them.

 

t

  • Thanks 1

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Got a significant oil leak... leaves a small pond on the ground after the car has been driven.

It appears to be dripping from between the engine and transmission.

 

Changed the oil, didn't start the car and there was a small amount of oil that dripped out over night.

 

 

20140720_111226_zps40004600.jpg

 

 

Your picture does not appear to indicate a significant oil leak.  Wetness is certainly not a good sign but it is far from unusual.  Same with a drip, although a few drips could easily disperse and seem far worse than it truly is.   But a pool or puddle is never a good sign.  Not that you haven't already thought of this, but starting with a clean floor rather than a veteran of many oil leak wars is probably a good idea.

 

 

If you did not start the engine after an oil change and you still have a leak . . .

 

I doubt it is your rear crank seal and I am not so certain your pan, pan gasket, or drain plug is at fault.  Since the oil level is typically slightly lower than both the crank seal and the pan gasket, it is hard to imagine how the oil would drip up and over those items.  A leak at the drain plug would be fairly obvious, even on a dirty engine, especially if the engine has been sitting and not turned over since the oil change.

 

A residual leak from the rear of the head seems somewhat unlikely unless the engine oil pressure is positive, as would be the case if the engine had been turned over and run. 

 

As Toby mentioned, without a set of eyes on the complete unit, something obvious is easy to overlook long distance.  For example, if the engine had a number of leaks (even easy to fix leaks such as a leaky dip stick tube), oil that had previously leaked prior to or as part of the oil change could be what appears on the ground.  If there was a very poor seal at the valve cover gasket, or a slight crack at the upper portion of the head in or near the valve train,  it may seem unlikely, but I could imagine a possible scenario where adding oil could leak out and drip to the bottom rear of the engine.  This seems implausible but nevertheless possible.  I have even seen a a cracked valve cover.  It had been used as a makeshift cricket bat. 

 

As another poster suggested, cleaning the engine thoroughy, with pressure, and then carefully examining things is most prudent.  For all we know, you have a leaky front crank seal that tends to accumulate toward the bell housing because it is the lowest point of the drivetrain.  Other giveaways might be wetness forward of the bell housing, on the center drag link.. It's not just gravity that causes the oil to matriculate.  Wind seems to have something to do with it too.

 

Best of luck.

NK2000motor.jpg

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Thank you for your responses :)

 

I always clean up the oil spill after moving the car so I know this is new and growing.

 

Drove the car today, put it on jack stands before it cooled down and removed the inspection plate.
Oil was dripping out of the bell housing.

 

There was also oil on the transmission and the center drag link...
I'll wash the engine tomorrow and check the front for fresh oil and report back.

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Drove the car today, put it on jack stands before it cooled down and removed the inspection plate.

Oil was dripping out of the bell housing.

 

 

A pinhole leak may seem much larger than it is when the leaking oil is under pressure.  It seems counter productive drive the car or pressurize the oil by running the engine.  From your earlier description I would think it might be better to clean the engine and place the car on jackstands without starting the engine and/or driving it.  Cranking the engine without starting it (pulling the plugs and cranking the engine a few times) - with you watching things - ought to create enough oil pressure to make the source of the leak fairly obvious.

 

Although I doubt it, could it be that your engine is cursed with too much pressure, making your otherwise nicely sealed bottle, blow its cork?  Did you possibly perform any recent engine work involving the oil pump or the oil filter housing support?  (Not saying this is the case, but throwing it out as food for thought.)

 

The idea of "leak detecting dye" suggested below, is a good one, but probably better used for detection of a slight drip or an ooze in a dark and (too often) dirt covered drivetrain.  If your leak is as significant as you describe it, and your engine is as clean ( e.g., as clean as MikeS' NASA-certified and flame-sterilized kitchen counter  :)  -  or cleaner), you probably can do without it. 

 

Good luck

 

 

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Edited by Roland
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I used these recently to track down an oil leak that had driven me crazy since I bought the car a year ago:

 

$(KGrHqZ,!rQE88hJNr7IBPlRd)F-h!~~60_35.J

 

Turns out my oil pan gasket and timing chain cover was leaking and blowing oil all the way to the back of the transmission. I tightened up the oil pan bolts a bit (they were loose) and I'll get around to the timing cover gasket one of these days ^_^ At least now I know where it's coming from.

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++1 on the clean engine idea  ( clean engines are much more enjoyable to work on and as Marshal says, easier to spot an anomaly. I use Foamy Engine Bright)

 

I chased a very similar leak on my engine this year.  I tore a cardboard box down flat and laid it under the car to A: catch the oil, B: help determine where the leak was coming from.

 

Like you, I could have sworn mine was rear main... nope. Was the dizzy O-ring and dizzy housing sealing-washer.  ( I also had a couple of weeping exhaust studs, just like Toby pointed out....damn, that guy is good)

 

To confirm it is NOT the dizzy, clean the back side of the engine up near the dizzy flange...especially along the bottom of the flange.  Clean it to the point a white paper towel is fairly clean.  After running the engine, go back to the under side of the dizzy flange with clean paper towel.  If it's wet with oil, you've found a leak... If wet near the top of the flange, it's likely the distributer O-ring, if lower down, it's the sealing washer. 

 

Hope you get to the bottom of it.

 

Ed

'69 Granada... long, long ago  

'71 Manila..such a great car

'67 Granada 2000CS...way cool

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