Packard Forum Index » V-8 (1955-56)

Of the other people running an Olds oil pump, has anyone found their rear main seal leaks after installation? That has been my experience thus far.

When I installed the Olds pump, I also installed a modern, neoprene rear main seal. This has proven to be an acceptable replacement for the rope seal, and I have confidence in it.

After I first put the engine back together, on a 30+ mile test drive I discovered the rear main seal was leaking (more like pouring). So I tore it back down and double checked installation of the seal, but could not find anything wrong. So I reassembled the engine, and now find it is still leaking.

This time I did the test "drive" with the car still up on ramps. Warmed up and at idle (45psi of oil pressure indicated), there is no leak; at 1300 rpm there is no leak. However, at sustained 2000rpm (65 psi indicated), it begins to leak in less than a minute, at a rate of about one drop every three to five seconds.

Looking at a spare engine, it appears the lube oil coming out the rear side of the main bearing returns to the sump via a slit in the bottom of the main cap. That slit, measured from out side is about 1 3/8" long X 1/4" wide. This measurement is deceptive though, since it is much smaller on the inside, plus the rear edge of the main bearing fills in some of the inner side of the slit.

My hypothesis at this point is at sustained higher rpm, the slit in the main cap cannot dump the lube oil being by the main bearing fast enough; the cavity fills up and builds pressure; itthen begins to push the oil past the seal.

My plan is to increase the size of the slit as much as possible with a dremmell and try it again. (But I am getting VERY tired of removing the oil pan.)

What say ye Olds pump wizards? :)

Joe H

JoeH: I will be the first to admit that I am no mechanic, and give very little advice on mechanical problems, but will throw in my two cents.


It seems to me that you oil pressure is way to high both at idle and at cruising highway speed. It seems to me that you pressure shouldn't run much over 45 or 50 lbs at highway speeds. I think at 65 lbs of oil pressure it is simply blowing it past the rear main oil seal. One question for you concerning this high oil pressure, what weight of oil are you using in the Packard. If your running anything more than 10W 40 weight oil, drain the pan and change oil to 10W 40 this will also give you lower oil pressure. Also to get some lower oil pressure you may have to play with the relief spring on the new oil pump.

John F. Shireman

Packard53 is giving u some good advice on the oil. If i remember rite, u said in another post some weeks ago that u r running 20-50 oil. Thats TOO heavy unless u're SUSTAINING 140-180 mph in 100+ degree ambient for many hours on end. The Packard V8 runs in the neighborhood of 180-220 degrees which is relatively cool to average.

I have NO rear seal leagage and i'm confident it has the factory installed rear seal. I just got in from a 60 mile round trip at sustained speeds of 70-80 mph in 97 Degree heat with temp gauge reading 180-200 degrees. Done it several times since installing the Olds pump. I'm running 10-40 summer and 10-30 winter.
Are u sure it's leaking at the rear main seal???? Maybe it's leaking at the pan seal at the rear main.

The rear main is the THRUST main for the crank. If the cap is installed without centering it relative to the thrust face then it is possibe that the rear seal in the cap is setting either forward or rearward of the seal in the block. This is not likely to cause a leak problem but could if rear main cap is excessively off center. There is no dowl to locate the cap so the cap CAN be installed to far forward or reward by the amount of slop in the holes for the bolts.

Check crank shaft end play to see if it is excessive or too tite.

Quite frankly, i believe the problem is the 20-50 oil if that is what u r running.

Also check the ADAPTER plate to see how close it sets to the rear wall of the pan. If i remember rite it sets over the drain slot in the cap but does NOT seal it off. In fact it mite be AGAINST the rear wall of the pan. U mite want to grind away a little from the rear side of the adapter to allow more free flow from the drain slot in the cap.

ON SECOND THOT!!!!
HOW did u install a NEOPRENE seal in the UPPER half of the block without removing the crank (ergo trans). Its been several years since i've installed a cheater type rear main seal but if i remember rite they were all rope type and i used a slim jim (wire cable tool) to draw it over the crank. Never saw one made of neoprene unless it was the type used when the crank was removed.

Thanks for the input. I have ran 20W50 and 15W50 in this engine 135,000 miles, and 30,000 in another 56J engine, so I don't think that is the problem. Unless maybe now, with a pump that has so much more volume. Even so, the pressure relief valve should compensate, but it obviously is set to open about 10 psi higher than the Packard pump. The higher psi and increased volume circulates more oil through out the engine; as I mentioned in an earlier thread, it increased oil drops from the rockers about five fold, so I am sure the same is happening at the rear main. I am thinking, with the cavity between the rear bearing and seal filling up faster than the drain slot can drain it, the oil has gotta go somewhere, and pushing past the seal is the easiest exit.

I forgot about the adapter block partially covering the drain slot. It is definitely not against the rear wall of the pan, but may well be restricting oil drain from the slot.

That's one problem with re-engineering, when one component is re-engineered it often calls for re-engineering related components. Its when we don't initially see the relationship that bites us in the butt. Then too, we know that no two Packard engines are exactly the same, so hopefully nobody else will have this problem. On the other hand, solving this problem may provide a quicker solution for the next guy who experiences it.

Soo, looks like tomorrow I will not only open up the drain slot as much as possible, and also check for drain interference by the adapter and grind accordingly.

I sure hope to fix the problem next time around. As mentioned earlier, it is no fun removing & installing the oil pan so many times.


Thanks Again,

Joe H

Trust me, FelPro seal, BS-40613 works as well in the Packard V8 as it does in the millions of GM cars and Jeeps its been OEM in since the 90s. It is also easily installed with the engine & tranny in the car.

That's the beauty of a modern seal, they slip right around the upper half of the crank. Unlike the OEM rope style, which is near impossible to install with the engine in the car.

The big three came out with retro fit kits decades ago for cars earlier fitted with rope seals. It was just a matter of finding one to fit the Packard engine.

Joe H

Before u tear into it and just as a test, try some 10w-30 to see if it still leaks. The thinner oil should leak worse if it's seal problem (it happens) and leak less if it's a drain-back problem.