MoMo

I need a question answered, if any engine gurus might know.

I just got my 427 running in the 68 Corvette. (Big Block 427). Because of our thin air in Colorado, I went with a large radiator and an oil cooler mounted behind the radiator. Then there's a remote oil filter mount under the oil cooler. Only rated oil line runs from engine to cooler to filter and back.
I also installed a Melling, high volume oil pump for a big block Chevy.

When I first start the engine, I get around 35 psi of oil pressure. I would have expected close to 60, but taking into account the length of the lines to the front of the engine bay, I suppose that could drop my oil pressure.
(Right or wrong?)

However, my concern is that when the engine warms up, the oil pressure drops to just above the zero mark, and on the stock gauges, they aren't numbered. Of course, when I rev the engine, it'll climb right back up to 30-35 psi.

Is this a reason for concern? Possibly a bad oil pump, or is it probably just because of 6-8 feet of oil hose length plus a huge cooler to go through?

mountainmotor

Whats the cST of the oil you are using @ 100C or 212 F ?

or just post the oil brand and advertised grade and we can go from there.

You do have a bit of pumping to do but initial thoughts are the pickup tube has a pinhole if it was welded,not properly mounted on the pump, a leaked caused from the use of the Moroso plate mounted between the oil pump and the main cap,lifter bore worn,cam bering issues from not sizing after install causing a tight fit and damage ect,the right oil sending unit is used if a electic type are a few things but really think if those are out of the equasion a higher VI oil will help matters .

CFI-EFI

In MY opinion...First things, first. I would beg, borrow, or god forbid, buy a mechanical guage of known accuracy. By accuracy, I don't mean specially calibrated or anythng fancy, just one that is known to work. Double check the situation with a reliable guage. Many factory guages are only slightly better (worse if they are misleading) than an "idiot light". Things may not be as bad as they appear.

RACE ON!!!

vetterod

I agree. If a reliable gauge still shows 0 at idle you have to find the problem. It could be as simple as the oil pick up pin hole. Let's hope. If you are running a good grade of at least 10/30 oil I don't believe increasing oil viscosity will help.
What are the internal rod and main bearing clearances and side clearance of the connecting rods of your engine? Big blocks set up loose (top end of recommended clearances) in these areas are designed to pass a lot of oil through the crank assembly. It's needed for cooling and lubing the extensive mass of this engine. Any clearance above the recommended, especially in the rod side clearance area, results in large reductions in oil pressure at idle. Not flow, but pressure. Some builders don't worry as long as you have 10 to 15 psi at idle with a full warm engine on big blocks. Keep in mind that rule of thumb is that at elevated RPMs you must have a minimum of 10psi pressure for every 1000 RPMs of engine speed. 6000 RPMs needs 60psi min.. Pressure at idle is not the only concern.

MoMo

Thanks for the replies guys. I am using about 8.5 quarts of Castrol GTX 10W30 oil.
I have checked the bearing clearances on the main caps with plastigauge and although I no longer remember the measurements, I remember everything was exactly to GM specs.

The oil pressure gauge is what I suspect. I don't think it's very accurate. I think I should get out an old Autometer oil pressure gauge and measure it separately to see what exactly it is.

What I do know is that when the oil is cold, I do get above 30 psi of oil pressure when I start the engine, according to the factory gauge. As the engine warms up, the oil thins out and the pressure steadily drops towards the bottom of the gauge. It's not at zero, but it appears to be just above.
When I blip the throttle even slightly, oil pressure immediately rises.

I think I definitely do have more than 10 psi per 1000 rpm. So maybe it's nothing more than thin break-in oil and a mile of oil lines to go through, plus a not-so-accurate factory gauge.

I left out one detail. Per recommendation from a Hot Rod magazine tech article, I drilled and tapped the hole for the pressure relief spring where the oil filter screws on, and plugged it with a screw-in plug. The purpose of this is to force ALL the oil to go through the filter, which in my case is remotely mounted with a large oil cooler in line.

427Hotrod

Well, I think I'd be pretty concerned. They are right...first thing try another gauge to make sure. I don't know....is the stock C-3 gauge still a mechanical one?

Any chance dirt got into line/opening to sender during installation? Pretty easy to do.

Where are you attaching oil sender/line to? Back of block? Front of block at main galley? Inline filter?

Have you changed filter? Assembly lube can plug one up pretty quick. This will kill pressure.

What filter are you running? Does it have an internal bypass? Most remote setups use a filter with one.

I don't think cooler line length should have drastic effect on oil pressure like this. Once it's full, it's full.

Does it return to original filter mount on block adapter?

Did you prelube it before installing in car? What did it hold then on drill?

Along with everyone else, check oil pump mounting surface on main cap. It must be flat. Also the whole pickup tube deal. Can't have leaks. Like sucking on a straw with a crack in the side. Don't work! Pump didn't bottom out somehow on oil pump stud or something?

How 'bout "Cavity" in cap under pump? No "porting" left a nick on sealing surface did it?

You might have to look at pump. I've talked to several folks with some "high end- high $$) pumps that are pretty sloppy internally on end clearance. In all cases pressre goes up dramatically once end clearance is reduced to .002 or so.

I've yet to get a bad Melling pump. Not saying it can't happen, but in 25 years haven't hit it yet.

Any chance trick distributor or something isn't engaging oil pump drive properly?

All the galley plugs in place behind timing cover?


My biggest fear is that there is some major clearance issue somewhere. Hope not, but you need to make sure it is fixed before you run it much more. HV pump with stock type clearances should easily peg 80 psi gauge cold and hang in the 70-75 range warmed up. 35-50 psi at idle is common unless things are loose somewhere.

Keep us up to date.


JIM

GregP

Long oil lines of proper size won't lower the pressure. The boat motors plumb through about 7ft of line (total) in going from block to oil coolers to remote filtes and back to the block. I have both mechanical and electric gauges at the oil filter mounts. Mechanical (inlet of filter) usually read 70 psi at idle and electrics (outlet of filter) show 60-65. After a long run when the oil temps come up it drops to about 50-55 psi at idle on the electrics.

I'd first check your gauge, but if not suspect a bad main clearance as that is quite low oil pressure from my experience.

-Greg

MoMo

Okay:

1. Any chance dirt got into line/opening to sender during installation? Pretty easy to do.

*Very Possible.

2. Where are you attaching oil sender/line to? Back of block? Front of block at main galley? Inline filter?

*To a pre-existing port just above the oil filter, on the driver's side.
There is no filter in line between the block and the gauge. Just a tiny plastic line.

2. Have you changed filter? Assembly lube can plug one up pretty quick. This will kill pressure.

*There is less than a mile on this filter. I'm still tuning the carb.

3. What filter are you running? Does it have an internal bypass? Most remote setups use a filter with one.

I am running a Fram PH8A filter, a big huge one that holds about a quart of oil. It's a size common to Fords actually.

4. I don't think cooler line length should have drastic effect on oil pressure like this. Once it's full, it's full.

*Yes that's true. But I've had one other Melling oil pump do this to me. It was on the 455 in my 68 Firebird, and the symptoms were identical. On a hunch, I drove it around doing a couple of full throttle runs, and it came "unstuck". I was told it could've been a stuck pressure relief spring inside the oil pump. I'm beginning to suspect that here."

5. Does it return to original filter mount on block adapter?

*Yes. It goes through the oil cooler, and then through the filter, then back to the adapter on the block.

6. Did you prelube it before installing in car? What did it hold then on drill?

Yes I did, for quite some time, using an old distributor shaft and a 1/2" drill. But because of my vantage point, I was not able to run the drill and look at the center gauge console simultaneously. However, I did feel the oil hoses vibrate from the oil flow. That's how I knew it prelubed.

***************************
I too am a little bit concerned about this. So this weekend, weather permitting, I'm going to take it out to try out my latest carburetor set up, and if it feels good, I'll goose the throttle real good a few times and try to get a more accurate gauge hooked up.

I don't think Melling's quality control is THAT good. This is the second pump I've had on two different engines with the same identical symptoms.

You're absolutely right about the phenomenon of trying to suck fluid through a straw with a hole in it. You don't get much. I don't know if that's the case here though.

Let me test drive it a little further than a half mile, and see what it does. It's kind of hard to really work the throttle on a car that goes sideways with the slightest blip on the throttle.

:D

71coupe

Try working the problem by process of elimination. The easiest would be to go get a different filter adapter (the factory one that goes on the block) & disconnect the oil lines at the block & install a couple of plugs. If the problem stays, I would check the torque of the oil pump bolt. If it's torqued, try to insert a feeler guage at the flange to ensure there's no gap.
After that if you are still have problems try installing a new pump.
Good luck

427Hotrod

Just paranoid me....but before I went out and winged it at all, I'd see some serious oil pressure on a gauge. These issues don't "grow back" once they are wounded. Only gets worse.

An oil filter can plug up in about 5 minutes on a newly built engine if assembled with lots of moly lube or lubriplate. I'd stick a new filter on for $3 and try it first. Don't worry about changing oil for this test. Just scrrew on filter. If it helps, change both after that. The extra solids are still in the old oil.

The Ford filters use an internal bypass.

Install a cheap gauge and check pressure.

Not saying Mellings are infallible, just my experience has been that I have zip issues with them while I've seen some mega $$$ ones be terrible.

Good idea on the feeler gauge check under pump.

Good luck....but if you go out and run it hard before you see oil pressure on a gauge, you're braver than I am.

JIM

MoMo

Just to ease your mind, I don't have to go out and run it hard before I see oil pressure. Just a tiny blip of the throttle and the oil pressure jumps way up. The Corvette goes sideways with just one fourth throttle and only in the primaries. I haven't had enough warm weather to completely tune it yet. So I have not yet run it hard, and I have not yet even driven it a mile.

However, your suggestion to change the filter is a good one. It's cheap, and why not? In fact, I could do that at the same time that I try another oil filter adapter. One very good Mopar guru friend of mine seems to think that introducing 10 or 12 feet of oil line that the oil has to go through full time could and probably does cause the problem. So what the hell. A new oil filter adapter and a new oil filter is a lot easier than trying to pull the oil pan with the engine still in the car. Because if I'm not mistaken, the entire steering assembly has to be dropped under the pan to get it off, correct?

Finally, I think I will go ahead and check oil pressure with a more accurate gauge. In fact, maybe I'll make provisions for an electronic oil pressure gauge that will permanently reside within the cowl induction scoop visible to the driver that will monitor the EXACT oil pressure, because I'm sure the OEM gauge lacks accuracy.

Know what? I could even run a little test. I could simply screw on a filter onto the block and see if that eliminates the problem. If so, that's pretty good verification that it's because of the mile of 1" oil lines that the oil has to go through. And from an engineering standpoint, that CAN have the effect of dropping some pressure. How much is the question.