Oil thermal reserve

[Anonymous]

I commute with my 200" falcon 50 miles each way every day. it is a stock 68 with a pertronics ignition. running .050 plug gap and ignition advanced to the edge. it will ping on the steeper hills at 70 if i get into it.

what i notice is a drop in oil pressure at sustained running at 70. the gauge will drop back to 20. if i slow to 65 for a couple minutes the oil pressure will always come back up to 40. I do not know what this means.

also i note that when i am running fast in that low pressure mode, if i back off the throttle the oil pressure gauge drops even further. then picks back up. the oil pressure light comes on for a couple seconds.

also on hards stops, at anytime, i gat get the oil pressure light to come on and the gauge drops to zero for a couple seconds.

This engine is running very well, however i would like to understand what is going on if any body understands these phenominae.

I feel pertty comfortable since I know what is inside the engine. new mains and rod berings and new oil pump.

i do know the shape of the oil pan, the location of the oil pump in the front and all is conducive to shloshing the oil forward on hard stops.

also it seems that i am also reading the oil filter bypass valve at times as it seems to vary with filters and possibly with oil.

I am running valvoline durablend 20/50 which is a synthetic blend. i am running this heavy oil due to bad seals; it seems to hold oil longer.

do you think i am actually exceeding the thermal capacity of the oil and overheating the oil when the pressure is dropping at 70?

can anyone shed any light on this? and or have any suggestions

thanks frankie

 

[CobraSix]

Sounds like you may have a couple of things going on.

First, if the light comes on at hard stops, you may be low on oil. Make sure you are full.

Everything kind of points to the fact your oil pump may be dieing or you have a blockage somewhere in the oiling system. Was the oil pump new or rebuilt? Sometimes you may just get a crappy one. Also, the gauges, are they electrical or mechanical gauges. Check these number out with a mechanical gauge. Electrical gauges can do funny things if they don't get the proper input voltage.

For thermal capacity, I would say you aren't exceeding it. What temperatures do you run at those speeds? Modern oil generally has no problems with thermal capacity on these older engines. I know I run my 200 at 75-80MPH with no problems, even when I had a cooling system problem. So part of me still thinks oil pump or blockage. There are some oiling system cleaners you can get. I've never run them. Basically, you do it 5 minutes before changing the oil (though no road driving, just on the lift, run 5 minutes and drain).

Slade

 

[Anonymous]

it is a brand new pump from auto zone. gauge is a mechanical gauge. It reads 20 at idle and 42-45 at speed. i tend to think these are good values. i do keep the oil up within a half quart of top. i think my dipstick is good since the motor takes almost 5 quarts when i change oil and filter.
i am tapping the oil pressure at the fitting at the lower left rear of the block right at the sender.
the old and new pumps were more or less the same in performance: i changed it first. then i went in and replaced the lower end bearings. which had brought my oil pressure up from 6 idle/ 22 at speed to what i mention above. this was 19,000 miles ago . motor runs fine ever since but i have always noticed about the pressure drops when hard braking esp when the oil is lower.
since it is a rear sump i can envision the oil slipping forward on hard braking and uncovering the pickup.
i was also imagining as you travel faster maybe more and more oil hangs up in the upper end due to gravity feed back to the pan. maybe there is still sludge in the pushrod holes in the block i did not noitce.
I did stay with the early falcon pushrods which are smaller in diameter and would be less restrictive to the oil return.
I do believe i am overlooking something, and i do not know what it is.

It is mildly disturbing to see the red light and the needle swinging down to zero. there is always air in the oil pressure line to the gauge. is this correct?

any body else out ther have the same symptoms?

thanks frankie

 

[Lazy JW]

I can't imagine 20/50 Valvoline synthetic oil to be breaking down under those conditions. Maybe something weird like abnormal crankcase pressures could cause this. Try a test run with the PCV port open and the oil breather cap off. It could be messy though
Joe

 

[Anonymous]

i have not received any remarks that suggest anyone has a similar situation. this is very baffling. I have had dozens of vehicles over the years and similarly performed my own work. i have never seen anything like this red-light situation.

I plan to put a cheesy lower-grade oil filter back on later today. hopefully at lunch so i can test on the way home.

at the moment i have a lighter grade of oil. as of last thursday i put in some 5-40 red jug that was on sale...exxon I think. since i had waited too long on my last oil change, i planned to make na couple quick changes in rapid succession to help flush it out.

i believe i have sensed that due to the way it is plumbed the motor is sensitive to grade of oil filter. the better rated filters get reduced oil pressure in only a few miles. junk filters like regular fram will only get a red light and low pressure when i am near 2 qts low.

when engine is cold and for the first 15-20miles at 70mph the oil pressure maintains at 42psi. whence the engine reaches up close to 180F
indicated, i will see the oil pressure hand start to get erratic. it will start to creep down toward 20. if i back off the throttle it will swoop to almost zero...red light for a couple seconds... then when deceleration levels out after about 10 seconds the gauge hand will start to sweep back up. to 20( (idle pressure.). If i reduce speed to say 65 it will hold oil pressure for many more miles before it starts to drop off. If I drive at 60 it may never drop off. i can repeat this cycle at will. speed-up, lose oil pressure /slow-down, regain oil pressure.

thinner oil makes it worse. lower oil level makes it worse. somehow the filter bipass valve may somehow come into play.

this scenario has exsisted for the 19000 miles since i obtained this car and got it on the road.

I imagine that the oil thins out to a point that it wont hold pressure as well. at higher speeds more oil is pumped into the top end and effectively lowers the oil level. thinner oil will also cavatate quicker at the pickup screen. thinner oil also sloshes forward over the baffles on deceleration.

is it possible that an anti-slosh baffle came loose in the pan? something that would aggravate this situation? i cant remember what it looks like now.

after i run it home tonite i will drain and change back to the 20w-50 durablend and see the effect. Then i will try the test with a breather stack in lieu of the cap and recirculating hose. this will give me true atmosheric
pressure instead of+/-0

I havent heard or seen any immediate negative effects as of yet but it is unnerving to be pulling a long 6% grade on kellog hill and suddenly get zero oil pressure when I have to back-off briefly.

I am open to any and all ideas

Thanks Frankie

 

[CobraSix]

I still think you have a bum oil pump. Just because you got it from Autozone doesn't mean it was anygood. I've bought alternators from them and they were bad when I put them on the car. You car does basically the same thing my truck is doing now. Drops oil pressure when the oil warms up. Generally, that is worn bearings or impeller in the pump.

Slade

 

[Anonymous]

but 20 psi at hot idle is not indicative of a bad pump.

i changed my oil filter at lunch and retopped it off with 20w-50 durablend.
it will run all the way home ( 50 miles)at 75mph without the oil pressure fall below 39 psi. the indicated temperature will be about 190 when i get half way home. the oil pressure will drop only if i decelerate very rapidly or if the oil level falls low 1-1/2 qt. but in a week or so ( as the filter clogs up again????) i will suddenly see a loss of cruise oil pressure from 40 down to about 20. slowing down only about 5-10mph to about 65 and the oil pressure goes back up to 40.
it is very strange and i have yet to convince myself what it is. however i am convinced the oil pump is good. i wouldnt get away driving it 500 miles a week for a year at top speed if the new pump was bad.
i need to hear some creative ideas. this isnt the usual worn out pump. a worn out pump follows a pump curve. this thing is following some sort of a bleed-down curve part of the time frankie

 

[Anonymous]

I have seen symptoms similar to yours. After operating temperature is reached oil pressure decreases on acceleration and increases on deceleration and this was constant, not back and forth like yours. It is worn mains. On acceleration the crank will move down, leaving slack on top where some oil can escape and not go through that oil passage, causing low pessure. On deceleration the crank will move up, closing that slack, forcing all the oil to go through the oil passage. With all that oil now going through that oil passage and not escaping, you oil pressure will increase.
I know this will be hard for some to understand just like some folks think 93 octane gas ignites quicker than 87 when in fact it doesn't.

 

[CobraSix]

You'd be surprised how long a bad oil pump will last. My explorer one lasted for 4 years, 50k miles and it actually still works most of the time. I have to pull the engine this spring.

The way you describe it the fact that it happens after a week, that is very interesting. Makes it sound like you have something really worn out in the engine cause premature breakdown of the oil. Try this test. Do a simple finger viscosity test (since I doubt you have a viscosity meter like we have at work). put a drop of oil on your thumb. With your index finger, dap it and start to pull it apart slowly until the oil doesn't hold together anymore. Now, after a week, do the same test and see if you are pulling it apart less distance before the bead breaks. It's kind of a backyard test of viscosity. Not as good as a real top of the time viscosity tester we have for diesel engines, but will give you an idea of the state of your oil at various stages.

Slade

 

[Anonymous]

Sounds like your oil pump may be dyeing or you have a blockage somewhere in the oiling system. Slade

Maybe the pick-up tube has become disconnected from the pump. Have you checked to see that you are getting adequate oil to the valve train? The last cam bearing has two oil holes, one feeds the rocker arm, both holes must be aligned or the oil supply to the rocker arm assembly will be cuts off.
I had a similar problem on my Jeep in line six. At idle, waiting at a stoplight the oil pressure would go down to near zero. Bring the RPMs up and the pressure would come back.
It was a bad sending unit. The oil was actually leaking out through it. Once I found the problem and got a replacement it was a five-minute job to replace it.

 

[61Futura]

All symptoms considered, it sure sounds like your pump is pumping it out of the pan faster than the oil will drain back into the pan. No solution comes to mind other than, well, tearing it down and cleaning the block & heads. And who knows if that would help.

 

[Lazy JW]

This one is a real head scratcher for sure I am beginning to suspect multiple causes.
1. You have already changed the "lower end bearings"
2. You are running good oil of fairly heavy viscosity
3. You have replaced the oil pump with a new one.
4. It only happens at high speeds and when decelerating
5. It gets worse a week or so after an oil change
6. You mentioned it is worse when oil is over a quart low
7. You never mentioned changing cam bearings

I am guessing that you are burning a fair amount of oil. Also that the oil is getting diluted relatively fast. This combined with loose cam bearings and high speeds is allowing the oil to be pumped out faster than it can return. I suspect that the oil pump would need to be in good condition for this to happen.
Joe

 

[MustangSix]

One other possibility is that you are pumping the sump dry at high speed. The oil could be accumulating in the rocker cover and unable to drain back quickly enough. This might be exacerbated by the PVC system creating too much vacuum in the rocker cover or by a clogged air breather.

Do you hear a lot of dripping oil inside the engine after you shut it down?

 

[Hot 6t Falcon]

You've done a super job analyzing an aggrevating problem.
You also have lots of good advice here.

Two more things to consider in easy-to-hard order.

1.) IGNORE THE DIP STIKS MARKS. When you change oil, put in all five quarts. Give the oil time to drain into the pan. Pull the dipstick and check the level. That is your actual "full" level. My dipstick was off 3/8 of an inch. I used a file to make a new mark.

2.) Is the bottom of the oil pan concave or convex? The bottom of the sump is 'spose to be convex (curved outward towards the ground) Sometimes people will put a floor jack under the bottom of the pan and bend it upwards. This causes the oil pump's pickup tube and screen to not have enough clearance. It needs about 3/8 inch. Otherwise at speed the oil will cavitate (create an air pocket because the oil can't flow to the pickup as quickly as the at-speed engine can suck it up.)

Good Luck

 

[PLP6400]

I was looking at the Ranchero Forum and a guy was describing the same problem of low to no oil pressure at high speeds. His rebuilt motor was still under warranty. The rebuilder told him that it was probably the oil pressure relief valve spring in the oil pump was bad and to bring it in for them to change it.