Notice to all Northstar Technicans; including the DIY crowd-

Rear main seal.

I have customer complaints regarding a leak from above the black plate that connects the engine and trans. I install them all the same way; I've taught my employees how to use the Kent-Moore tool; all flywheel bolts are sealed as well.

Four instances in a short time.

Customer of mine; also my life insurance agent; came by for an oil change about 9,000 miles after a complete re-build & re-seal. The pan was bone-dry; no seepage or drops. Nothing.

Friend of mine. I called him this evening. No leaks. Another friend of mine; black 97 Aurora. No leaks. My dad's '01 DTS, no leaks. Another two owners of '99 STS's that I know; I inquired. No leaks.

But these four.

I cut a GM rear main cartridge seal apart and also a Fel-Pro seal. The GM seal has a smaller lip and allows the oil to run into the drain; the Fel-Pro seal holds more oil instead. The GM seal uses a softer rubber compound. The Fel-Pro; hard rubber compound. The GM seal has a double rail seal with an extra lip. The Fel-Pro; only a single.

Nevertheless; some cars are leaking and some are not.

The #5 rear crankshaft journal is fed oil through the main bolt holes; like the rest. All of the oil fed to the #5 main journal/bearings HAS to run around the rear main seal and down through that drain hole.

Oil level.

If the oil pan is overfilled, that drain passage begins to fill up. This means the crankshaft seal area begins to fill up and the oil pressure; at anywhere between 8 psi and 70 psi depending on engine temp and RPM, is forcing that oil under pressure out the rear main seal area and also forcing it through the drain. If the oil level is kept at the proper level, the oil will drain freely into the pan.

I had a complaint about a car that was dripping bad. I took it back and checked. Had it running for a 1/2 hour. Two drops on my concrete shop floor over that time span. Nevertheless; that wasn't right. I figured "ok. Time to pull the engine again". I drained the cooling system and let the oil out. Between 12 and 13 quarts of oil came out of that crankcase.

Right now I'm at a loss.

I always make sure that drain hole is free of blockage of RTV sealant and whatnot; so I think I can rule that out.

I've been doing extensive R&D on what's going on all afternoon. This has to be remedied before I proceed any further. I've taken the bottom part of an engine and filled with carefully measured oil. With one of my factory-equipped dipsticks and tubes; 1 liter overfilled comes up as "exactly full" on the dipstick. One liter (just over a quart) over full brings the level very close to that drain back for the rear main seal.

I will post pics soon- you can see exactly in the photos; how far oil comes up in the pan when it's full.

This $h1t is not supposed to be happening. I need to find out the cause and the cure REAL fast. One of those four cars is coming back to me tomorrow because of an oil leak. Last one was a blown power steering pressure line; we'll see what's up with this one tomorrow.

Even if the Fel-Pro seals are holding up; I'm not sure if I want to continue using them. The GM cartridge seal seems to be twice the quality of the Federal Mogul manufactured unit.

I believe in keeping costs down; as long as the parts I use are still top quality. Fel-Pro is supposed to be the best in the aftermarket; but I don't care; with the amount of work to split the engine and trans; money is no object when it comes to the rear main seal. It's near $100 here in Canada for the GM part. I get a bit of a discount; not a whole lot; but some.

This is the correct level when full. 7 quarts or 6.6 liters (without filter, with a filter it's supposed to be 7.5 or 7.1 liters). Keep in mind an oil pick-up tube is normally sitting there in the center.

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The owner's manual speaks about proper oil levels and indicates that the upper hash mark is the highest the oil should ever be.

The subject of MANY posts in here, the current GM TSB for FWD Northstar oil fill procedures also gives specific guidance for oil level.

The result of all those words is that the normal oil level indication for a Northstar engine, properly filled with 7.5 quarts of oil, is just about halfway up the dipstick hashmark :

<----ADD XXXXXXXXXXX OPERATING RANGE <-------

If you habitually carry the oil level at or just above the top hash mark you are running the engine with 0.5 to 1 quart overfill, and that's also addressed in the TSB as being a contributor to complaints of excess oil consumption: The engine will rapidly burn/leak that extra oil, so if you attempt to carry the level at the top hash mark you're simply throwing oil on the street. In truth, a Northstar will be perfectly happy with the oil at the bottom hash mark all the time. I carry the level at somewhere between the bottom mark and halfway and get 4,500 miles to a quart of Pennzoil 5W-30 synthetic.

Here's a hint: I use MILODON 8-quart pans on my marine Olds455 engines. MILODON says - "Fill the engine with the recommended pan volume of oil. Prefill the oil filter. Run the engine, shut down and check oil level. The observed oil level now on the dipstick is the proper FULL level. Mark the dipstick at that point."........ If you change your Northstar oil, prefill the filter and pour in exactly 7.0 quarts of oil you will see the dipstick result.

Yes. What Sub stated is correct in my eyes as well; that if the drain-backs are already full of oil; the oil pumped around the heads, etc. has nowhere to go. Either it leaks it out or has to burn it.

Four concerns regarding oil leaks is too much in a short time. It is my job to re-seal these engines so they will NOT leak.

I have one back here from Detroit right now. Blown power steering pressure hose. The mechanic this guy took it to could not pinpoint the leak and insisted it was the engine timing cover seal. If you turn the steering wheel; the blown line shoots out a steady stream of fluid; right on the accessory drive belt. It soaked the whole front of the engine; and travelled along the engine. The rear main seal area is dry- I checked with a flashlight and see no signs of leaking.

The GM rear main seal is considerably a better design IMO anyways; even if the Fel-Pro seals are holding up. List price in Canada is $94. I get a bit of a discount; but GM Parts Direct in the USA lists them FAR cheaper. I want to see if I can put in a volume order and get it below that amount.

I checked again with a couple of past customers today. No leaks.

The customer from Toronto who was going to bring his car back to me today for inspection of the leak had to cancel out. I'm hoping he will send me an email letting me know roughly where it's leaking from.