Hey y'all, i have a 1966 Mustang with an old 289. I just hooked up a
mechanical oil gauge after replacing the oil pump drive shaft. When i
first start the car, it reads just above 45 PSI. After it warms up,
the pressure just drops to 0. When i rev the engine, the gauge kinda
moves up a bit, but not too much.
I notice in the tube that runs to the gauge there is a lot of air,
should i try to bleed this out?
Should i replace the oil pump?
Is there a better way to drop the oil pan without having to remove
that fat crossmember and lower those steering linkages?
On 30-Jul-2004, firstname.lastname@example.org (Errol Smith) wrote:
I've installed a few oil gauges (I always drive old cars and install
mechanical gauges) and have never had to bleed the oil out of the line to
the gauge. Besides, as soon as you shut off the motor the oil will drain
back down again. If you have pressure when cold, but not when hot, and you
have an old motor (I'm assuming high mileage) you probably have loose
bearings. Maybe not loose enough to make a lot of noise, but loose enough to
let the oil pressure drop when it heats up.
As to lowering the oil pan, try unbolting the two engine motor mounts and
jacking it up with a block of wood against the oil pan. Jack it as high as
you can and then wedge wooden blocks in the motor mounts to support the
engine. Sometimes this will give you enough clearance. But you'll still
probably have to unbolt the pan and then reach inside blind to unbolt the
oil pump. Then you can probably lower the pan.
According to an old Chilton's, just unbolt the pan, but on some models
you'll have to unbolt the pump before you can remove the pan. Sounds easy,
and it is. But bolting it back together isn't nearly as easy. LOL
More Chilton notes- Disconnect stabilizer bar from lower control arms and
pull ends down. Unbolt pan and drop to crossmember. Undo one inlet tube
bolt, and loosen the other. Swing inlet tube up to provide clearance. Turn
crankshaft as required for clearance to remove pan.
Every day is a good day- it's just that some are better than others.
The air in the line makes absolutely no difference. As a matter of fact, if
you bleed it, it will have air in it again within a short time. You have a
worn out engine. If it truly is zero at idle, that's not really good,
because you'll be starving the rocker arms, but ANY pressure at idle at all,
and you'll be ok until you can arrange an overhaul.
uh... nice try... the viscosity is fine on startup, too thin at temp. going
to 30 aint gonna help if he was using a quality oil to start with. There MAY
be only one or two worn bearing.. though probably all. And 30 isnt enough
for wide gaps... that's why they still sell "racing oil".
After a certain point, MORE oil flow becomes a bad thing.
let's just agree to disagree. you follow grandpa's advice based on "everyone
And I'll counsel him to try a 20w-50
And I am probably your grandpa's age (early 60's) and can say for sure that
most old-timers are fulla shit!
Whatever.. so YOU are the grandpa, so am i... my advice stands.
Quality 20w-50 till rebuild. You need to SEE some oil pressure at hot
idle... if you dont you are flowing too much oil.
and NO freaking additives or gear oil!
Based on 40 years experince maintaining my OWN cars which I
expect to still have more than 2 years.
And the ability to think and read.
If you do not see any pressure, you have very LITTLE flow very big leaks or no
pickup. No flow = no pressure. Low flow with larger than normal leaks = low
pressure to no pressure. No oil to pick up = no oil pressure. Bottom line flow
is a good thing.
Symptom: "45 lbs when cold, 0 lbs when hot"
Think about some practical lube system physics and get back to us with your
Recall that i changed my original opinion... to probable mix of worn/bad oil
pump and some bearing wear.
And TOO much flow CAN equal no oil to pick up.. but not in this case.
Too much flow equals increased foaming at operating temp.
Everything I said is the basic laws of hydraulics. The pumps job is to move
fluid ( flow ), pressure comes from the restriction of that flow. No or low
restriction = no or low pressure; flow goes high. The symptom fits the second
law. low flow with a leak = low to no pressure. Even a pump that is in good
operating condition you will not have pressure or low pressure if there is a
large enough leak that the flow of fluid is not opposed ( that would be caused
by large gaps between worn bearing surfaces ). High resistance = low flow high
pressure. Low resistance = high flow low pressure. Want to prove it? Put a flow
meter and gauge on a garden hose. Turn on the water and let the water flow out
the end unrestricted, then partially plug and full plug the end watch what
happens to the gauge and meter.
Lost in all this is the possibility you really have a worn oil pump, which
with some bearing wear makes it looks worse than it really is.
My advice is still the same... 20w50
depending on your means, you could get by with just a new pump for a while...
but you have to pull the pan anyway. Plastigage the bearings, esp the mains,
while you are at it.
Here's the key... listen closely at cold start.
If you hear ANY evidence of a deep sounding knock until the pressure comes up
you have significant main bearing wear. If not count on at least new oil
pump. Like I said, plastigage!
Im running 20W-50 presently for the bad rings. Theres no knocking when
the engine first starts up, but im pretty sure the bearings are all
worn. Ive been driving the car around now on the freeway and there are
no problems whatsoever. I would think that if i had 0 oil pressure
that my lifters would drain and my valves would start tapping. The
cars temperature stays right at 180 also. If the pump were bad,
wouldnt it not read normal pressure at startup?
Thanks for the help!
the pump can still pump and works better (pressure) because of the relative
viscosity, both in pumping and the lower flowout through the bearings.
In fact, your pressure bypass in the pump is probably working initially.. you
would then see a gradual but quick drop as the engine warms.
Nonames physics are right but theres a good chance that the pump is the main
culprit if you dont have mains clatter on startup.
You have to pull the pan to fix it anyway.. check the mains and replace the
pump.. re my prev last thread.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.