"Spring pressure behind the bypass valve determines when it will open. If it is designed to open at 60 psi, it doesnt have any effect on anything below 60 psi - UNLESS IT STICKS OPEN - if it sticks open pressure will be low at idle and then build up to the 60 psi at which point the valve would normally open."

In theory maybe..in practice I think you'd find most stock pumps will open way before that.

 

Oh absolutely. if the bypass spring for example is in the pump when the pickup is brazed into place one could easily weaken the spring. In a circumstance such as that replacing the spring is excellent advice. The point is adding a higher pressure spring to replace a standard pressure spring will have no effect in this case if the standard spring is undamaged.

If it is damaged (i.e. weakened) or even sticking....replacing it is a perfectly appropriate step.

 

The OP didn't say that he had "10 at idle", unless I missed it.

If there is only 10 psi with 10 miles on the motor, then,
Pretty much has to be one of these.

-faulty gauge (1st to check)
-the relief valve is stuck open
-bearing clearances far to high
-welch plug under rear main oil galley missing
-welch plugs under timing cover failed/missing
-oil pump pickup tube cracked/loose/plugged
-damaged oil pump
-problem with distributer housing (oil galley)
-filter and bypass plugged/missing

 

If the plug is missing under the rear main cap the oil bypasses the filter once it full as it can not bleed of any where as I have seen this posted before.

Here is a link to look over
http://speedtalk.com/forum/viewtopic...er=asc&start=0

Here is a test I did on a crate engine

 

Yes, I'm aware of all that, a lot of opinions, but have never known of anyone to do a real test other than you.
Yours was a BB?
I always put the plug in, even partial filtering is good.
I know driving a plug too far, in past the step, can create problems too.


Here is a quote from
John Lingenfelter's book Modifying Small-Block Chevy Engines

"don't forget the little 1/2" oil galley plug found under the rear main cap. If left out, it will create an internal oil leak that can reduce oil pressure by 20 psi."

Although, his engine reputation is probably beyond reproach, it's a shame he's not around to confirm his statement.
Nonetheless, it's something the OP can check.

 

Thanks for all the tips.
The gages and sending units are all new and I checked the oil pressure with a mechanical gage.

I checked the battery cables and while they looked like new they were 4 gage. I replaced with 0 gage and the car starts much better, not perfect but a lot better. It took me two days just to change the wires. There must have been a better way but I ended up removing the transmission to replace the positive battery cable and associated clips.

While reinstalling the transmission I had a jack stand break. There was an air pocket in the casting and the “Y” part holding the car split in two. Thanks to whoever suggested putting the ramps under the tires. It scared me good but the ramp caught the car before falling any more, just the distance of the suspension travel. I took the jack stand back to sears they actually gave me my money back even though I kept the jack and creeper that came with the jack stands. I am going to get some high quality ones now.

As far as the oil, thanks 63mako, I checked the shop manual, according to that I should be running thicker oil so I am going to change the oil to 20W-40.

page 1-12
Temp
Min below 5deg 10W-30
Min between 5deg and 32 deg 20W-40
Between 32deg and 95 degree 20W-40
Over 95 degree 20W-40

The oil pressure is not linear, there is a jump at 750 rpm. It jumps 10 psi real fast. This is under load as well as in neutral. The oil pressure gets up to 50psi at 3500rpm, I have not gotten above that as this is when the car shifts.
The oil pressure does not drop before rising, or if it does I can’t see it.

As far as who built the engine, the company lost there shop while rebuilding the engine. I started by installing the intake and harmonic blancer. The guy was not very good, he had the car for a year and all he did was rebuild the engine.

I was reading about the rear seal and it is on my to do list, just wanted to see if there was anything oil pressure related I should do at the same time to save pulling the pan twice.

I plan to replace the radiator and fan clutch this weekend, I am hoping that will help with the engine temp. If not I will give it some time and hope it cools down as the engine brakes in.

 

Here's the oil plug were talking about, if you leave it out the filter will fill but get bypassed once it is full. The oil pressure will not be any lower or higher but the oil in the filter will not circulate thru the motor. With the plug correctly installed the oil is sent thru the filter and back thru the motor thru the second passage. If you leave the plug out the filter will fill and then the oil will go straight up into the motor.

 

Mine does the exact same thing as your but it is a BB. My mechanical reads 20-25 at idle when warm. Electric is reading 10-15. When revving or driving it goes up to 50-60 and settles back when at idle. I am the engine builder so I can't pin it on someone else...

Glad you didn't get hurt when the car fell. That has always scared me.

Wade

 

Great post as there are a lot of write up abouts leaving that plug out and low or no oil pressure and more guys beleive what they read but don't have a clue how the SBC oils. Even GM wrote it in one thier manuals.

Again great post
Carl

 

If you mean its jumping from 10psi to 20psi (at 750 rpm) and then proceeds to reach 50psi by 3500 rpm then I would say run the 20-40 as indicated in the manual and you're probably fine. While you have the pan off to fix the rear main check the pump inlet pipe to make sure its securely fastened to the pump.

 

I agree pressure shouldnt be different, there is one drawback I can think of however. Most if not all oil filters have an anti-drainback valve, which would prevent oil still in the galleries at shutdown from draining back through the filter into the pan.

Without that prevention I could see much of the oil in the galleries being able to drain back to the pan and perhaps even out of the pump. I am certain that some drainback occurs anyway so I'm uncertain how big a drawback that could be.

 

It's very surprising that John Lingenfelter didn't understand this, building and selling many hipo chevy engines, but yet publishing that in a book.

 

This is true no presure change with the exception that you may have the drain back problem and low presure till it fills again as you point out. Not so sure why people want to dream things up about how things work, maybe cause they do not look at the way the systems works and just make assumtions. In this case if the plug is left out you only by pass the filter. Oil and anything such as air will just take the path of least resistance in this case bypass the filter only.With that said one could see a slight difference in presure because of less restrictions of the oil not going through the filter.

 

Ya because he probably read it in the GM manual and did not think about it. DON'T BELIEVE ALL YOU READ

Look at what Smokey Yunick wrothe that to much side rod clearance will affect oil pressure HMMM any one that knows about performance engines knows its the bearing clearances which regulate how much oil comes out between the rods not side clearance.

Also I built some piston guided rod engines that have .100 plus side clearance and have not seen any oil pressure lose yet.

 

On the side clearance issue your right it will not lower the presure no matter how big the side clearance but you do have to have enough, without enough you can reduce the flow out of the rod pack and that an't good! And yea your right some read way to much without thinking about the problem.