Niles,
Shame on me for not including that. Yes we did change the sending units, three times!

However, this is another clue...

The plot thickens :)

DV -- 300 Cobras ARE not enough!

THE VIDEO'S OF THE DVSF I ARE AVAILABLE !

Oil Pressure problem
 

If you checked the gauges then I'd have to agree with Niles that the sending unit would be suspect. IF they were electric gauges. If they were mechanical then it could be an obstruction. If its not an indication problem ie the gauges check OK then I'd suspect the end play gap on the oil pump gears was incorrect. I don't know how the Dodge pump is set up but my Buick Grand National has the same kind of pump where its in the front cover. My buddy is a Chevy guy who checked his Grand National's pump and measured it like you do a Small block ie the gears are countersunk EXCEPT on the Buick they stick out of the housing. When he started his engine oil pressure was fine. As soon as the oil began to heat up the pressure would go into the toilet. He pulled the motor checked EVERYTHING including the pump. Again he checked it like a small block Chevy which he has built MANY. Again Motor back in car start it and the same thing. Could cause insanity. Finally sat down and looked at the BUICK manual and about crapped when he read how to check the gear end play. Uggghhh...

Wrong filter could do it, also an obstruction in the oil cooler.

On a different note I couldn't agree more with Niles about not trusting any one gauge. On any airliner if you get low oil pressure there is also a light. It should come on at the redline. Also Oil temp will begin to rise if the pressure really starts to go away. But its simpler in a large jet you can simply shut down an engine as a precaution (but not because of one gauge indication) on the DC10 or 747 its really a non event.

Regards,

Bob,

No obstructions. We used mechanical and electrical for testing with the same results.

The oil "pump" ended up being fine, in fact the original one was probably fine!

Oil temp. has nothing to do with the "improper" reading(s).

Think off the wall here...way off!

This may be so far off the wall no one will get it. We'll see.

DV -- 300 Cobras ARE not enough!

Video's of the DVSF I are shipping!

pressure
 

DV:
I suspected you had just omitted the the sender cause; too simple and obvious.
Clearly you have a very obtuse and diabolical culprit at play here!

HOW about too much assemble lube creating obstructions or anomolous indictations?

gn

"anomolous indications"

Now we are getting close!
The plot thickens....

pressure
 

English vice metric?
gn

Nope!

Should I drop the dime, or wait a day or two?

DV,

I am fine. Getting really into it. Bought a Contemporary Classic project with 427 SO.
We also bought seven Cobras already and shipped them to Europe.

I have seen the Hi-Tech factory - amazing!

Oil pressure:
you experience a drop right after start-up?
It may sound blunt, I would let it run without oil-filter if the filter itself does not have a bypass (or if you blocked it).

Some filters Peter used were on their edge when new already. We found out during practise and got it confirmed by Lee Miur, the 60s McLaren mechanic.

They were set up for full flow.

I changed mine for the bypassed version.

Good luck,

Dominik

Dominik,
Another excellent thought...but nope, not the filter.

OK, last clue. All three guages and senders, (mechanical and electrical) were working properly. We DID in fact have oil pressure at all times. It was the third guage that finally solved the problem.

The question reviewed: Why did two guages show 75/80 lbs of oil pressure at start up, then drop to +/- 10 lbs, while the 3rd guage showed full pressure immediately and through out the engine break in?

For what it's worth: The motor was rebuilt using all new parts including a very special crank. (More on that later and WILL come into play with the oil pressure issue)

The incredible story behind the rebuild: See above posts. Totally assembeled, including plugs, minus the transmission, it takes less than 40 ft. lbs. of torque to turn the motor over by hand! Is the motor built tremendously "loose?" Not on your life. Unbelievable, very, very close tolerances.

DV -- 300 Cobras is NOT enough!

DV
 

You seem to be pointing at the "indication" side of the mystery in yet you said that you tried both electric and mechanical gauges which "indicates" to me that you got something in the passage that feeds the fitting to the oil pressure pickup as you stated that the motor had full pressure at all times.

Silicone? An obstruction could allow the pressure to initially show high and then drop...

This is one of the things I like about a forum like this. You can learn from other people experiences.

Regards,

Bob,
Nope, thought I made that clear as mud in one of the other posts. Absolutely no obstructions, as I said we eventually found that we did have pressure at all times.

Lets go one more time:

The false reading WAS because of a guage(s), but the guages work perfectly and no obstructions!

Think, "pressure!"

Now that should do it! :)

DV -- 300 Cobras is NOT enough!!

DV
 

You mentioned that the "special" crank had something to do with the pressure. However, the motor was never without pressure and that the gauges were finally found to be incorrect (first 2) third gauge showed pressure normal.

It might have something to do with changing the gauges finally "fixed" the problem. But you said there were no restrictions. So it can't be something like Teflon tape blocking the passage.

Hmmmm... all I can think of saying is I'm glad it wasn't me:)

Ok lets hear it as I've got to go down and finish putting my Grand National back together...

Also the "kid" is bringing over his Big Block 66 Vette so "Dad" can find the oil leak. Fun job, thank God I've got a lift.

Regards,

Ok DV, I'll give it a try. Was the issue do to the size of the sensor orifice? And did a larger orifice fix the problem?

Petek,

Lets say you and the anomolous indicatior are almost there, but not quite. :)

It is one of those problems that is soooo stupid, you could kick yourself when the answer finally becomes clear!

Think pressure! ( last hint...a lot of pressure compared to a normal engine!)

DV

300 Cobras is NOT enough!!

DV,

Ok, 'nother guess: teflon sealant causing a loss of ground on the sender ... until enough pressure was placed on the sender to overcome the insulating sealant?

Hmmmm,

This is the last hint! :)
Remember guage #1 and #2? If I were to reinstall them, the same scenario would pop up! Pressure would go up to 80+ then fall down to 10 +/-. Both guages are working properly.

If I install guage #3, we will and f do get a proper reading.

It is SO easy! :) ....... now!

DV

Gauge(s) not matched to the sensor (i.e. positive vs. negative coefficent).

the three gauges act as pressure reducers and so the third reads correctly???

Scott

Scott,
I thought you had it for a minute! But no, not really. We did not hook up the guages in a series.

Ready for the answer?

DV -- 300 Cobras is NOT enough and by golly we're going to get there!

DV
 

You did say that both mechanical and electric type gauges were used and they showed the same pressures. So that should eliminate teflon tape problems unless you had a fitting that was obstructed and that fitting was used on all of the gauges up to the last one. Also you could have filled the 1st two gauges with sealant and the stuff was gone for gauge 3. That is why the first two would still show the problem but 3 doesn't.

Is the oil pressure pickup point near the pump on the front of the motor? The reason I ask is mine was like that on the Cobra motor and I moved it to the rear of the motor just off the rear cam bearing figuring that I wanted to see the pressure at the "far end" of the oiling system not at the pump. It really shouldn't make a difference other than with my dry sump I "Prime" the motor by cranking it until I get 50psi (about 5 seconds) then I pump the gas to get it to fire. Its easier than spinning the Weaver pump with an air rachet.

OK DV put us out of our misery...
Can't wait to hear the answer as I've got my climbing boots sitting here ready to really give myself a "kick"...

Regards,