lyonsh

Here's one I haven't seen before. We decided to put a more powerful engine in the Vette. Fired it up and were running it at 2000 rpm to break in the cam. It was running a little hot, but that's not unusual during break in.

Here's the problem. After about 10 minutes, the oil pressure started dropping. It dropped steadily from 50 psi to 20 psi over a period of about 30 seconds. After it got down below 20 psi, we shut it down. Other than the oil pump breaking (please, no!), I'm trying to figure out what the problem might be.

Right now I'm frustrated and not thinking straight, so I walked away from the car. If anyone can provide some options, I'd appreciate it.

:cheers:

71coupe

is it a new block?


[Modified by 71coupe, 8:27 PM 5/9/2004]

MotorHead

New motor, who built the motor, do you know what main bearing oil tolerances were ? Ws it still running OK, just low oil pressure ?

One easy thing to check first is pull the distributor and check the gear make sure it has not worn the teeth down. :D

turtlevette

hate to say this but could be a wiped out bearing.

71coupe

If it is a new GM block, there is a plug that needs to be installed in the rear/cam area. There is a note in the current Scoggin Dickey catalog in the block section that warns about this missing plug & low oil press. If someone has a current catalog maybe they could reply about the exact location (I'm at work right now)

checklst

Drop your oil pan and check the pick up!!!!!! and measure the pan clearance to make sure the pickup screen is not sucking down on the oil pan bottom cutting off the oil supply.

Also like Motorhead said check the dist gear(you did install the proper gear) brass or steel its all up to the cam you installed.

Right now that's all I can think of that simple

Super Stock

Also if you are sure the gauge is accurate , then maybe the rear main bearing spun ? Was it due to the oil getting hot and a pressure drop ?

R 73 454

I would pull the distributor, put in a "oil priming pre-luber". Pull the valve cover and see if the oil at least comes out the pushrods/rockers. Maybe something simple, like oil guage malfunction. Ugh, good luck! :cry I would also pull the filter, cut it open and look for bad stuff. :bb As far as the heat, make sure you get any air pockets out of heads when re-filling coolant. I leave the temp sender out or stat. out until the coolant bubbles out. :banghead:

checklst

:iagree: with 73454 now would be a good time to use an external oil pressure gauge to verify the sender/gauge, and remove a valve cover just to see a little flow with your eyes, it will make you feel better seeing the flow.

lyonsh

Thanks for the ideas, guys. I've cooled down a little now, and will get back on it tomorrow.

To answer the questions so far, I built the engine (I don't do this for a living, but it's not my first). I checked all the clearances at least twice, and pre-oiled the engine before starting. I'm hoping it's something simple like assembly lube clogging the oil filter. At least I have a few things to check now.

corvgreg

When I was very young and so was my friend that helped me build my first performance engine(a 12.5 to 1, tunnel-rammed Z28 302), he installed the oil pump and pan while I was away one day. We did the rest of the engine together. We had the same thing happen to us...I ended up pulling the pan and found the oil pump sitting in the bottom of the pan. He installed the pump with a bolt one size smaller in diameter than should have been and it let loose after a few minutes. Oil pressure was fine and then it steadily dropped until it hit zero.
I hope it's something simple...

Greg

Mr.Gearhead

Manassas... hell we are neighbors... hee hee...
I broke my cam in today as well... 60 psi for 20mins. I was told by my engine builder that my small block should never see under 25 psi. He said to shut it down and run the preluber to check. I assume if you get +25psi during prelube... it isn't the pump. If you don't get 25psi, then it might be the pump. Also, I noticed when prelubing today... the push rods OOOOZE oil like crazy... I ran the drill and modified old distributor for 1 min to get things started... :steering:

pws69

I had EXACTLY the same thing happen when I first started my fresh 350. Turned out to be the Oil Pressure Gauge!! Gauge was reading fine, then slowly dropped to zero! I think it was a little corrosion on the brass movement. I took the gauge out , soaked the movement with WD40 then applied a light pressure on the little brass "pressure tank" until the needle moved off zero freely. Put it back in and it has been working great ever since.

Before you start ripping the engine apart, verify that the gauge is still working.

68raggtop

One more easy thing to check is that the end of the tube (on mech gauge) or sending unit (on electric) didn't pick up some junk that is restricting it. Also, if using teflon tape, make sure it didn't cover any of the end. Been there- done that. Hope it all works out with an easy fix. :cheers:

LemansBlue68

Also check the pickup tube and its connection with the oil pump. These are pressed in, and with an oil pump replacement you often have to pull the pickup out of the pump and press it in to the new pump. When doing this I ALWAYS braze or weld the pickup tube to the new pump. This does two things: it seals the joint so no air gets pulled in and it assures that the pickup does not work loose from vibration later on. You can never get that press-fit as tight the second time due to wear and deformation of the tube. Also check your oil pressure relief valve to make sure it is not stuck open from lint or dirt left over from shop rags etc. I hope you don't have a spun bearing.

lyonsh

Yep - me too.

UPDATE: I think the pump is good. I pulled the distributor out and spun the pump with a drill/priming tool. The pump is pumping oil (splashing all over the rockers), but the guage isn't registering. I'm hoping there's just something stuck in the guage plumbing. That's my next little adventure.

And thanks for all the help, guys - I appreciate it greatly. :cheers:

jamiejamison

First thing I would check is the filter, could be collapsed. After setting awhile and then restarted or in your case spining with a drill you would get oil for a short period. Good luck. JamieJ

RHD '68 L89

When you were using the priming tool did you feel the oil pressure against the tool or did it spin freely to get the oil to the rockers? If there was "backpressure" from the oil when priming and the gauge didn't register then it is most likely the gauge (or electrical sender if you have one of those)
Good luck and I hope it is the gauge.
:cheers: