Date: Tue Aug 16 14:21:49 1994   
From: John De Armond
Subject: Mysterious oil leak 

>I put some synthetic oil in my '73 240Z, and it keeps on dissappering.

Yup.

>I've check everywhere and there doesn't seem to be a large leak. I'm 
>putting in 5 quarts of oil about every 1 1/2 weeks.  The only leak I can 
>see is a really small leak at the end of the Oil pan, but everytime I 
>park the car I don't see ANY oil dripping on the ground.  With the rate 
>at which the oil is dissappearing, there has got to be some kind of evidence.

It's going past the rings just like it does in most Z engines.  About
like kerosene would.  Put good old 10W30 back in it and the oil consumption
will disappear.

John

Date: Thu Aug 18 11:31:29 1994   
From: John De Armond
Subject: Re: Mysterious oil leak 

>you mention 10W30. I use Castrol GTX-2 which is rated at 20W50. As far as I
>know I am getting the viscosity of a 20 weight oil when cold and the
>viscosity of a 50 weight oil when hot. Am I using too thick oil ?
>Could this damage my engine or cause high fuel consumption or poor economy.
>Would moving to 10W30 be an improvement.

Won't damage the engine but it will slightly hurt economy and will make
cold starting more problematic, if you have to worry about that.  20W50's
what I pull out when I am trying to avoid an overhauls for a few more
months.  After that, if I'm REAL lazy, it's 120 wt gear oil :-)  My
old El Camino which hasn't had oil pressure for a couple of years now,
contains 120 wt gear oil.  Boy, does that sucker stink when it smokes!

John

From: John De Armond
X-Source: The Hotrod Mailing list
Date: Jun 1992
Subject: Re: carbon fiber

>-> Smokey Yunich claims in his book that weight in the valvetrain
>-> upstream of the rocker pivot, ie, toward the cam, does not matter. In
>-> absence of evidence to the contrary, I see no reason to argue with
>-> him.
>
> As far as sprung weight, no.  You have to watch what Yunick says very
>carefully sometimes.  In his book he's generally talking about roller
>cammed race motors or disposable NASCAR motors.  (use 'em once and
>rebuild)

You ought to read his book on the subject.  "Smokey's super horsepower
secrets" or something like that.  He spends a lot of time detailing
the research he's done on the subject including high speed photography
of various valvetrains.  Since his thrust in the rest of the book is
building an economical endurance engine, I don't much think he's
talking dispos-a-motor.

Disclaimer:  Since I fool with motors with overhead cams and lifters
that weigh ounces, I am SWAGing this one.

John

PS:  While I have this message open in the editor :-), to the guy
who has a motor that's leaking quarts of oil to the mile.  You're
describing the tired old motor in my El Camino.  He has no oil
pressure, is knocking a rod and pukes out about a quart every
600 miles or so through the rear main.   Since I'm planning on
dropping something somewhat interesting in this vehicle, the engine
has become an experiment to see what I can do to it.  20W50 knocked
the leak and the rod knock down quite a bit.  90 wt did even more.
Yup, I'm running 90 wt diff fluid in the beast at the moment.
Cranks a bit slow but it actually has oil pressure for a few minutes
while cold :-)

I'd suggest dumping some 20W50 in the thing until you can fix it.
I'd NOT suggest using 90wt if you have any oil pressure at all
right now.  For a pump and bearings in good condition, the
extra load could break the pump drive shaft.

John