more oil leak questions

My mechanic says it is probably leaking at the engine case joint.
Heres my question. If that is the case , shouldnt the leak be fairly consistant ? The reason I ask, is that I have noticed that if I drive it normal, it leaks a very small amount overnight, however if i take it
and run it up to 80 or so pretty hard, and bring it straight back to the garage, it leaks a big puddle- looks mostly on the drivers side.
This makes me think it is leaking somewhere that there is oil pressure
like a sending unit or something.......................where is the sending unit? Does any of this make sense?

i would guess the engine block split is leaking, all northstars leak here. running the car hard thins the oil and slings a lot more oil to this point. there are guys who make a living doing these block splits! the oil pressure switch is very close to the oil filter to the right. it probably does leak as well along with the rear main if this car has some miles on it. theres no fix other than pull the trans(my method, some like to pull the engine) and do it. they may tell you that they need to install thread inserts for stripped bolt holes, this is also a normal concern

I hate to think that my block is leaking at 100000 miles. Everything looks dry including valve covers, rear main and oil pan. Mine has a small drip somewhere between motor and firewall on drivers side. We have pumped this car up and cannot find the leak from top to bottom. Does anybody know anywhere else on the back side it could be leaking? Is the oil sending unit on the back side? Any suggestions before I take this monster in would help. Running the Valvoline 75000 mile oil, I'm running out of places to look. Oil runs down and exits around the back lower front frame mount. Can't tell exactly where it comes from but the heads, oil pan, valvecovers are dry as a bone. Got to be something else. Comments welcome....

I hate to think that my block is leaking at 100000 miles. Everything looks dry including valve covers, rear main and oil pan. Mine has a small drip somewhere between motor and firewall on drivers side. We have pumped this car up and cannot find the leak from top to bottom. Does anybody know anywhere else on the back side it could be leaking? Is the oil sending unit on the back side? Any suggestions before I take this monster in would help. Running the Valvoline 75000 mile oil, I'm running out of places to look. Oil runs down and exits around the back lower front frame mount. Can't tell exactly where it comes from but the heads, oil pan, valvecovers are dry as a bone. Got to be something else. Comments welcome....


Sounds like you have the patented case half oil leak that the Auroras are famous for. Well what to do about it is mostly up to you. The case half leaks are seepage leaks and are not pressurized. So it will not cause you mechanical or driveabilty issues. Basically it will just leak oil and make a mess depending on how bad yours is leaking. You can spend a few thousand dollars and have it replaced or you can live with the leak. I chose to live with the leak. It really isnt that bad and in the winter it is almost non existent. I just clean the underside of the engine compartment maybe once a year and keep some cardboard under the car in the garage to keep the floor clean. Also I probably put 1QT of oil in between oil changes. To me its not worth the few thousand bucks to fix this. Of course the amount of oil coming out is different on each vehicle and would effect your decision.

I have also heard that the synthetics or max life motor oils can make the leak more pronounced compared to conventional oils.

If the oil leak is from the split case, there is
a TSB out about it. They have to pull the
engine and open the split block, clean the
seal face, put in a new seal and (ready for
the magic ingredient that fixes it all?) use
Permatex sealant outside of that. Then
they just close it back up and put it back in.
A few thousand dollars later, no more leaks from
that joint, ever.

Most 1995 and early 1996 Aurora's had a design
issue that caused this. Once a leak started it
typically would get worse over time due to thermal
cycling and degradation of the seal. Mine got so
bad after about 2 years of ignoring it that I was
losing about 1 qt every 10 miles or so, right out
the side of the block!

I had my 1995 serviced about 3 years ago and have
not seen a drop of anything since.

GuMan

WOW, 1 QT every 10 miles.

Mines pretty much been the same about 4 years now. Like 1 QT every 5000 miles in the summer and pretty much nothing in the winter.

Guess Im just lucky

Thanks, I noticed only a drip twice, the last two days no drop. I agree, I'm not going to pull this V8 out, it doesn't seem to be losing any on the dipstick, however it gets a change every 3000. Funny thing, it never leaked until I dropped the Valvoline 75000 in it. Been running durablend and Castrol sometimes full systhetics with not a drop. I almost thought it might be brake fluid but don't seem to be missing any. (It sure did look clean to be oil in a motor with 100000.) Guess I'll keep my eye out.

Castrol Synthetic had been a group III synthetic,
which is known to attack certain rubbers used in
seals. Mobil 1 used to be this type, but now they
are in group IV. Typical group IV oils are Amsoil,
Red Line, and now Mobil 1.

They put inhibitors into group III oils to keep this
issue at bay. However, the additives degrade and
by 3500 miles, they start to fail. This is why
I would not recommend using any group III oil
for an extended duration use.

Group IV synthetics actually swell rubber seals
slightly, like the additive you can put in your
power steering pump to help stop leaks. If your
oil leak is small, and only due to seal shrinkage,
you may be able to stop it with a group IV oil,
or an additive that has this same effect.

When my oil leak was being fixed, I had the
dealership flush out the oilways with the bottom
crack case open. Of course, they cleaned out
the bottom crank and pan too. We just opened
the valve covers and oilway cleaner down through
and let it clean up all the crud and drip right out
into a catch basin.

Once it has been sealed up, I had them use Red
Line 10W30, and I have been using it for 6K
intervals ever since (50K miles since then)
with not a drop!

GuMan

Come to find out, it was the oil pan. They loosened all bolts, applied lock tight retorqued, no leaks. Also had valve cover gaskets replaced. Nothing like 130K with no leaks.