I don’t believe it’s possible to have a rear main seal not leak

[BladeBronson]

I’ve owned two DeLoreans and have had rear mains replaced probably 5 times between the two and they always leak. Have any of you ever had success in not leaking oil? If so, lie to me and tell me how you did it.

[Bitsyncmaster]

Mine does not leak but when I replaced the clutch, I did see the drivers side cam shaft cover had a little oil leak. Have you looked for oil traces from that area? That cover leaking would make you think the rear main seal was leaking.

[Patrick C]

Mine used to leak, but as Luke Sandel predicted, after converting to EFI and adding in a true PCV valve (compared to the stock setup), the oil leak completely stopped. Crankcase ventilation is definitely a factor in the leaking.

[vwdmc16]

Its a tricky seal but it is possible, Ive done half a dozen of them, still holding for now.

Is it possible the transmission input seal is leaking? Mine did that after my first transmission re seal, in which I didnt change the input shaft seal. Only when it got hot did it leak, really looked like a rear main leak.

[DMC-81]

When I refurbished my transmission, I decided to replace the non-leaking rear main seal as I didn't know it's history. I chose new ribbed rear main seal from PJ Grady, and used "right stuff" gasket maker on the paper seal.

As installed:


After second gearbox removal (with flywheel bolts and without Nachi pilot bearing shown):


It's been holding up well in the 3 years and 3,000 miles since the restoration.

[FABombjoy]

For sure, proper crankcase ventilation is essential to solving some of these leaks. The original PRV / K-jet fixed orifice solution is just not great to start.

-Cleaning the air/oil element inside the oil cap housing should be at least an annual process.
Volvo calls this part is called the flame guard but it spends most condensing oil from the crankcase to minimize oil burning.
Someone posted a pic on one of the FB groups and it looked like it had been encased in jello.

-Avoid breather filters or other setups that remove the big hose from the incoming air stream. Since the orifice is not very functional at mid to high engine loads, the big hose is the only route out of the block. There's a tube setup in to the air box to further facilitate the process.

[Delorean Industries]

We offer both an updated rear main seal design on our engine builds along with a complete crankcase ventilation system and catch can configuration. The updated rear seal housing is applicable to a stock 2.8/3.0 block. We also use this on all rear main seal service work as well. This was originally for forced induction applications, but it simply became easier to incorporate it across the board.

[Bitsyncmaster]

Mine used to leak, but as Luke Sandel predicted, after converting to EFI and adding in a true PCV valve (compared to the stock setup), the oil leak completely stopped. Crankcase ventilation is definitely a factor in the leaking.

Many years ago I tried to install a PCV valve. I drilled and tapped a hole in the passenger side valve cover and hosed a PCV valve there. It ended up sucking to much oil into the intake so I had to remove it. You would need an oil cover inside the valve cover like all the engines do to eliminate drawing oil. I tried this also thinking the better crankcase ventilation would help reduce oil leaks.

[FABombjoy]

Definitely would need a baffle and probably air/oil separator if tapping the valve covers. Lots of oil fling there from the chains and cams. Based on the grease that forms on the intake ports these just seem like really oil-vapor happy engines.

The challenge with K-jet is that using manifold vacuum for PCV means having your tap downstream of the throttles, and K-jet needs a baseline adjustment for the unmetered air. Using the fixed orifice method makes the "leak" predictable.

With a real PCV valve the volume of air through the valve will change depending on load which leaves a functioning Lambda system as the only (crappy) balance to maintain AFR. It might get dicey on transient throttle inputs and lean at full load.

With EFI the variable flow just disappears into the fuel map and you really don't think twice about it.

[David T]

The crankcase ventilation system works BUT, only up to a point. If you have large air leaks or are getting excessive blow-by it will not be able to handle it. The 'fix" is not to improve the ventilation system, the fix is to find and fix the leaks or the cause for the excessive blow-by. On one car that had a turbo system, it got over-boosted and cracked the pistons. That car had so much blow-by, when you got into boost it would blow the oil cap right off and spew oil out. An extreme example. Point is, if everything is working correctly the crankcase ventilation system should keep the crankcase slightly negative preventing oil leaks. A major cause for that rear seal to leak IMHO is that at some point many Deloreans sat and did not run. That causes the seals to get a 'set" and once you start running the motor again, the seal leaks. Other possible causes include using the wrong type of oil (synthetic will leak if an old car is suddenly changed to syn) or too much oil.