289 reads no oil pressure

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?
Thanks!
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snipped-for-privacy@hotmail.com (Errol Smith) wrote in

Well, duh! if there is air in the line, I guess you should bleed it.
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Try bleeding the OP feed line to the gauge first. Most likely though, it will be a main bearing problem that's preventing the buildup of oil pressure.
Errol Smith wrote:

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On 30-Jul-2004, snipped-for-privacy@hotmail.com (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.
Have fun.
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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.
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Forgot to mention. 86 the damn multiviscosity oils and use a good name brand straight 30 weight.
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Steve Barker opined in

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 knows".
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!
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It has nothing to do with my dead grandpa's opinion. It has to do with my 30 years experience in fleet management of trucks with small gas to large diesel engines.
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ahh, the heck with arguing.
Just toss some 80 weight gear oil in it. You'll get pressure, or you'll snap the drive shaft. No guts no glory. Maybe a 50/50 mix with the 30 weight?lol
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Steve Barker opined in

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.
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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.

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noname opined in

Symptom: "45 lbs when cold, 0 lbs when hot"
Think about some practical lube system physics and get back to us with your modified opinion
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.
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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.

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Backyard Mechanic opined in

Well... shit!
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!
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Steve Barker opined in

go to a quality 20w50 till you rebuild.
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unless a 66 mustang is your transportation to work, no oil pressure no drivey, dont even bother with a different oil weight just rebuild it before you break something.

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The type of oil delivery system a car engine has, no bleeding is necessary.

No, you should find out why the oil pressure is low.

If you do not want to do the work, or it is too hard for you, you can pay some one to do it for you.

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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!
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Errol Smith opined in
If the pump were bad,

no.
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.
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