I did my weekly engine run and started seeing excessive oil pressure when I increased RPMs, 60 psi at idle and then maxed out the gauge, 80+ psi at 3000 rpm. It went down to 50 psi at idle and then suddenly lost all oil pressure, but continued to run normally. I shut it off and let it sit for a while, then started it to check the pressure and found none. Engine has about 6 hours total on a custom build. Any thoughts or opinions on this?

 

Check the oring on the pan pickup. If it becomes pinched it will cause havoc to the oiling system. Can you confirm from your builder that they used the appropriate oil barbell?

 

I’ve gone over everything in my head and the thing that has me stumped is that the pressure was too high then completely lost pressure in an instant. The oiling system consists of a new Melling pump, an Improved Racing baffled pan, pick up tube girdle, and cooler adapter. I have also considered the barbells which would explain the loss of pressure, but I believe that it would have had no pressure from the first start. I could be wrong about all of this. Another interesting thing is that the engine does not act like it is starving for oil, no extra lifter noise, bogging down, and the fuel pump continues to run. I have the Dakota Digital pressure sending unit installed at the cooler adapter and the ECM gets it signal from the stock location, I have not verified the pressure from the ECM, just the gauge. There is a slight leak near the filter where the engine transmission bolt together. In the end, the engine has to come out, that sucks.

 

So what exactly is the gage sensor measuring? Engine oil pressure, or pressure in the cooler feed line? Other?
It's going to eat at your mind not knowing how the 2 sensors compare. Maybe give the engine a quick start and see. (I'll bet you did already. )

I know the gage itself will read high if there is extra resistance in the wiring circuit. I assume it will read low if there is an electrical short, but I'm not sure without looking at the troubleshooting guide in the GM service manual.

Any time I had a rear oil leak it was the oil pressure sensor on top of the engine. First time it was just plain loose. I guess I didn't tighten it enough. Second time the sensor was actually falling apart. I swear it was held together by a prayer and wish when I got to it.

 

What type of pan do you have ? Dose it have a bypass built into it ?

 

I talked to the machine shop that put the engine together this morning and we agreed that I first have to determine the actual oil pressure with a mechanical gauge (I had planned to do that today) and we'll work from there. He brought up a good point in that he's never seen an engine suddenly have 0 pressure, even with a hole in the side of the block you'll get some pressure. As far as the oil pan, it's a GM F-body pan that has a sump baffle. The oil pump is a Melling with a 65 psi relief spring, which is why the 80+ psi spike is suspect. I'm hoping it's the Dakota Digital sending unit, or the location I have it installed. I'll post updates soon.

 

Well, if that DD sending unit works anything like my DD speedometer signal converter then it's a little g-g-g-g-g-g-g-g-g-glitchy.

 

Good news, and QwkTrip wins the diagnostics award. I got the car up and took a look underneath and found the clamp holding the knock sensor and oil pressure sender wire harness to the block had melted which allowed the wires to hit the header. While this explains the “sudden oil pressure loss”, it does not address the excessive oil pressure. The heat from the header may caused increased resistance in the gauge wires, giving a false reading. Unfortunately the entire exhaust system, including the headers has to be removed in order to fix this, but it beats having to pull the engine. I’ll post the results when I finish. Thanks to everyone who posted a reply.

 

Wire resistance probably glided upwards as the wire took heat damage being in close proximity to headers. The final nail in the coffin was the event that shorted wire to ground and that's when gage plunged to 0 psi.

 

Now that you've found something sodomized, JUST FIX IT. Don't get all hung up in over-analyzing the symptoms. THEN, if all the other supporting stuff is known to be working right, and the gauge(s) still indicate some kind of fornication, THEN AND ONLY THEN, descend into "maybe it's this or maybe it's that".

 

Sofa, I think you replied to the wrong thread by accident. But not all is lost because now you get to make another post full of demeaning, sarcastic, yet still meaningful advice! Your day just gets happier and brighter by the moment, man!

 

See, this is why I've never liked electric gauges.
I remember when the pressure sending unit went out on my first truck, and I **** a brick; thought I was going to need a new motor on a highschooler's budget.

Took it to a guy I knew, and he gave me the good news that it was just the sending unit. He recommended putting in a mechanical gauge, so I did, and WOW, the needle on the gauge actually moves around!

 

This is for anyone using the Improved Racing oil cooler adapter with a Dakota Digital oil pressure sender and long headers. I put various extreme heat sleeves on the hoses and wires in the area, but I needed to do something for the adapter. My solution was this aluminum heat shield that is bolted to an unused threaded boss on the side of the engine. This should help.

 

Wow, I didnt appreciate just how close that tstat was to the primaries. Neat little heat shield, I'll have to copy that.