I was cruising along at about 60mph today and heard a loud pop, kind of like a rock kitting the windshield, and then the oil pressure steadily dropped from around 60psi to a little under 20psi. I babied it home about 2 miles and checked the oil and as far as I can tell from the lokar dipstick, the oil is fine. I don't know if the sound had anything to do with this or if it was just a coincidence. Anyone know what this could be? I only have maybe 3000 miles on the fresh motor.

 

With 4.10 gears at 60 mph I am under 2k RPM.... My oil pressure is usually never over 20 if I'm under 2k RPM.

I stay pretty consistent with the 10 psi per 10k RPM.

And did a rock hit your windshield, or did the noise come from the engine?

60 psi at 60mph on a warm engine is pretty damn high if you ask me.

 

Given the specs of his engine, I suspect he has a high pressure oil pump.

Did you replace the plastic retainer for the oil pump drive with an upgraded part?

 

I changed to 3.23 gears recently. It sounded like maybe something hit the firewall or under the cowl maybe. I didn't see any rock chips, but it did sound very similar to something solid hitting the hood or window. I believe the motor has either a high volume or high pressure oil pump, possibly both. I'd have to look through some old posts to see what I went with. Its been a few years since I built this motor so I don't remember all the little specifics like that. What is this plastic retainer your talking about? I think it was a melling oil pump and I'm pretty sure I used an aftermarket oil pump drive shaft, but I'd have to either tear into it or find the receipt from when I bought it. I'm using an MSD oil drive gear like this. Oil Plug Wet Sump Chevy V8 - 8513

My oil pressure is usually pretty high with the oil that I use, which is German Castrol 0w-30, but I know that the pressure steadily and somewhat quickly dropped off soon after I heard that sound.

 

The stock oil drive (sometimes referred to as the dummy distributor shaft) uses a plastic top part, which is the retainer. There are metal replacement drives available. The plastic can crack, and allows the drive shaft to mesh incorrectly with the drive gear on the cam, stripping the gears.

Courtesy of Shoebox:





From Ellwein racing engines:



Doubt that it would make a loud pop when it broke, but it would explain low oil pressure.

 

I have a msd oil pump drive so I'd hope that nothing with the actual oil drive broke. I just took it for a drive and the oil pressure is around 40psi on a cold start but after driving for about 30 minutes it'll drop to around 10-12psi at idle. It climbs with rpms up to about 35psi at 4000 rpm, but I remember it being a lot higher.

I also notice engine temps were very hot today and yesterday after I noticed the low oil pressure. I'm sure the high temps aren't helping oil pressure. I checked the coolant and its full but after a 30 minute drive temps rose to around 230º when I was backing into the driveway. It was also higher than normal yesterday. I can hear the electric water pump running, but something isn't right because the fans never turned on and it never got that hot before.

 

Is the plastic air dam still in place under the front bumper?

 

Yeah, but its trimmed down a bit since I'm lowered 1 1/4" and I dropped the radiator mount crossmember to accommodate standing up the bigger griffin radiator. Its about as close to the ground as it can be. Its closer than the stock setup. I don't have that plastic piece that goes on top of the radiator and I also don't have the other piece that goes in front of the radiator that directs the air damn flow through the radiator.

 

Loud pop could have been a head gasket letting go which would explain the overheating. What kind of drive gear is on that MSD distributor drive, is it bronze or composite because bronze gears wear fast and could have broken a tooth causing the lowered oil pressure especially if you have a hv oil pump? In any event I wouldn't keep starting or driving it, pull the motor and check everything out.

 

Those things that are missing are going to compromise the proper air flow into the radiator. The stock system funnels air from under the car and directs all of it to the radiator. Your missing baffles lets air escape.

 

Are you running a converted Gen 1 intake manifold? That "plug" plugs the hole in the manifold for the distributor. Or is it something "similar" to that plug?

In any case, it appears to have a bronze gear.

 

hearing a "pop" and now low oil pressure would suggest something in the oil pump drive broke. You will have to pull intake to see if that in fact happened.

With that said I don't really know if you could hear a oil pump shaft collar or gear "break"....

A stock oil pump drive shaft has a plastic collar and if re-using the old one the plastic collar can crack on re-assembly because it has dried and fatigued and will break. Most just buy a ARP or Mellig solid steel drive shaft for around $12.

Also if the bolt (#66 in shoebox pic) is over TQ it will crack/break the plastic top of the oil pump drive gear (#65 in shoebox pic) and that gear will lift up resulting in no/low oil pressure

your cooling issue...maybe do a leak down or compression test to see if a particular cyl is down

 

I know this is a really old thread, but I’m hoping you can tell me what the issue was. I just experienced the exact same thing. Loud pop and then a drop in the usual oil pressure (although pressure is still in normal range - it used to run a little high). Also, oil levels are normal. Any advice or info is much appreciated!