Dropping oil pressure in new engine......

[fred cook]

I have just finished a rebuild of my SC engine using the original block, crank and oil pump. The cylinders (LN Engineering, pistons (Mahle), heads (Carrera Twin Plug) and rods (rebuilt by Ollie's to standard and balanced) are replacements. The crankshaft measured standard on all of the rod throws and main bearing journals. The original engine had standard rod and main bearings in place when it was torn down and made good oil pressure. Now, since the rebuild, the engine makes acceptable oil pressure when started from cold but within about a minute or two, the oil pressure will drop to about 1/2 bar at idle and will only make about 2 bars of pressure at 3,000 rpms. I have replaced the oil pressure gauge sender (helped the readings some) and just removed the oil pressure relief valve on the bottom of the block to make certain that there was no obstruction (wasn't) and that the valve piston moved freely (did). So far, I have driven the car about 2 miles or so. The engine seems to run well, pulls strongly and doesn't make any "bad" noises. At this point, there are no significant oil leaks and the engine fires up quite easily. I have not run it enough to do any final tuning or check the fuel pressures. On the short drives, the engine temps only got up to about 180 degrees F. Any thoughts or suggestions on the oil pressure issue would be appreciated!
This seems to be the same problem that is being chased around on the "Help No Oil Pressure" thread. ( I hope that I got that right!).

[otto_kretschmer]

2 bar is about 28 psi

so 28 psi at 3000 rpm follows Smokey Yunick's 10 psi per 1000 rpm

I wouldn't worry about it but if you must worry, switch to a heavier oil

[Green993]

I respectfully disagree about not worrying. 1/2 bar at idle is not right. This issue with it being good on cold start up is explained by the fact that the oil is very thick when cold. When it warms up, that thickness is lost and hence the lower pressure. Recommend you find the cause of this pressure issue. What was the idle pressure before rebuild?

[thumbdoctor]

How is your sump drain cover oriented? Is it obstructing the pick up screen? BTW high oil pressure is over rated, on an air cooled, flow is important to augment cooling. High oil pressure robs horsepower. 10 psi per 1000 rpm is adequate if bearing clearance is on spec.

[Green993]

One way to rule out the sender is by attaching an external pressure gauge at the sender and reading the pressure directly.

[mreid]

My 2.7 must be tired. It shows 50 psi at start up and then slowly drops to 0 once fully warm (200 degrees), but sits at 30 on the highway.

It sounds like your problem is different in that it happens so quickly unrelated to temperature. Is that correct?

[fred cook]

Originally Posted by Green993

One way to rule out the sender is by attaching an external pressure gauge at the sender and reading the pressure directly.

I did that by removing the gauge sender and connecting a mechanical oil pressure gauge. The mech gauge showed that the old sender was indeed going bad and needed to be replaced, which I did. The mech gauge showed the same results, normal looking pressure at startup w/ decreasing pressure as the engine was running. Almost as if the increase of oil in the tank was related to the decrease of oil in the sump.

[fred cook]

Originally Posted by thumbdoctor

How is your sump drain cover oriented? Is it obstructing the pick up screen? BTW high oil pressure is over rated, on an air cooled, flow is important to augment cooling. High oil pressure robs horsepower. 10 psi per 1000 rpm is adequate if bearing clearance is on spec.

I think that it is on correctly, but that is certainly worth checking!

[Walt Fricke]

Fred - you don't say what oil you are using.

In my usual contrarian way, I have never bothered with break-in oil. Just put the synthetic 20-50 in there and drove the car. Other than strange issues in a discussion I think you have looked at with a race motor built from disparate parts from here and there, and a GT3 pump, never much of an issue.

So I share the view that 1) 10 psi per 1,000 rpm is adequate, and 2) will you move to a higher viscosity oil once you are satisfied that it is time to move away from your startup oil?

I see the key here to be that your pressure rises with RPM. At least things are trending as they should, and not the baffling rise to a fairly low X, and then not rising more as engine speed increases.

Pulling the sump (luckily your '80 has the plate, although as suggested it can be installed incorrectly and cause problems) might help. Did you pull and reinstall the piston oil squirters? If one was spat out, chances are you'll find it in the oil when you drain the case. Did you install the cam oil line restrictors (yes, I know that probably you put back on what you had, and which worked fine, before the rebuild).

You might want to do the draining first, before removing the left side overpressure relief plug. That passageway connects with the bottom of the case sump, so - unlike the vertical one - when you pull that plug and the piston comes out, I believe you will drain most of the case anyway.

Good luck - all of us who have had puzzling oil pressure issues not solved with something simple are pulling for you.

[JJ 911SC]

Originally Posted by Walt Fricke

... Did you install the cam oil line restrictors (yes, I know that probably you put back on what you had, and which worked fine, before the rebuild)...

Walt

I had to read this twice to figure out what was implied.

I switched to oil line restrictors last time I had the engine out (3.2) and it did boost the pressure giving a reading of ~1 Bar per 1K Rpm which is probably what everybody expect.

Fred

2 Bar at 3K, what do you have at 5K?

[fred cook]

Originally Posted by Walt Fricke

Pulling the sump (luckily your '80 has the plate, although as suggested it can be installed incorrectly and cause problems) might help.
Good luck - all of us who have had puzzling oil pressure issues not solved with something simple are pulling for you.

Walt,

The more that I think about the way it is behaving, the more I believe that I may have installed the sump plate incorrectly. That will be the next thing that I check. It is acting exactly like it is starving for oil once the excess oil is pumped from the sump into the oil tank. And, I have already changed from 30wt to 20W50 wt oil. This engine might set a record for oil changes in the first 100 miles or so!

Thanks to everyone for your suggestions and observations.

[fred cook]

I retained the original (large orifice) oil restrictors. It seems logical to me that having a bit more oil vs a slightly higher reading on an oil gauge is the way to go.

Oil pressure at 5K? Don't know, haven't revved it that high yet! At the moment, that is where I have the XDi rev limiter set, though.

Originally Posted by JJ 911SC

Walt

I had to read this twice to figure out what was implied.

I switched to oil line restrictors last time I had the engine out (3.2) and it did boost the pressure giving a reading of ~1 Bar per 1K Rpm which is probably what everybody expect.

Fred

2 Bar at 3K, what do you have at 5K?

[Lapkritis]

I'm going to have 4 oil changes inside the first 1000 miles after my job so you have some catching up to do. The 4th change is because I discovered my oil tank drools onto the exhaust around corners so I'm replacing... figure it doesn't hurt as long as I keep running dino instead of synthetic until done with the break in period.

[Lapkritis]

Oh and oil pressures. 10psi per 1k rpm is fine. So idle when hot will be gauge near the bottom line of 10psi. I agree with the line of thinking that flow>pressure on these so the cams and rockers are getting plenty of spray without restriction. What exactly are you expecting that you aren't seeing? I would ask the same of the other gentleman who has raised his concern of a similar issue. I see 30psi at 3k rpm hot with 15w oil. Hot idle is near the bottom line or 10psi. Had always been this was even prior to service and with previous owner. You may be chasing castles made of sand. /jimihendrix

[jsveb]

Originally Posted by fred cook

I did that by removing the gauge sender and connecting a mechanical oil pressure gauge. The mech gauge showed that the old sender was indeed going bad and needed to be replaced, which I did. The mech gauge showed the same results, normal looking pressure at startup w/ decreasing pressure as the engine was running. Almost as if the increase of oil in the tank was related to the decrease of oil in the sump.

I bought a wet gauge and hooked it up in the same position as the factory sensor. I did this by tapping into that little block where the oil press. sensor and cam tensioner feed joins up. My gauge is temporarily mounted where the wing nut on the engine fuse and really panel normally screws in.

[Steve@Rennsport]

Fred,

For clarity, did you split the cases?

Did you remove & clean the oil cooler?

If so, what gasket set did you use?

Were the crankshaft's oil passages cleaned?

[fred cook]

Originally Posted by Steve@Rennsport

Fred,

For clarity, did you split the cases?

Did you remove & clean the oil cooler?

If so, what gasket set did you use?

Were the crankshaft's oil passages cleaned?

Yes to all the above. I used the gasket set from Pelican Parts. I went out to the shop this morning and I think I see the problem. I believe that I may have installed the sump plate incorrectly. Next step is to drain the oil and pull the plate and strainer off. Since the oil pressure starts out good, but drops as the oil tank is filled and before the oil has a chance to get more than warm, it seems to me to be a problem in the oil circulation. If it turns out that I made such a bone headed mistake I will be both angry with myself and relieved that the solution did not require disassembling the engine again!

[thumbdoctor]

Originally Posted by fred cook

Yes to all the above. I used the gasket set from Pelican Parts. I went out to the shop this morning and I think I see the problem. I believe that I may have installed the sump plate incorrectly. Next step is to drain the oil and pull the plate and strainer off. Since the oil pressure starts out good, but drops as the oil tank is filled and before the oil has a chance to get more than warm, it seems to me to be a problem in the oil circulation. If it turns out that I made such a bone headed mistake I will be both angry with myself and relieved that the solution did not require disassembling the engine again!

Here's having my fingers crossed for you Fred, I've caught that problem and damaged sump screens on many P engines for the problem you have and overheating in high ambient temperatures

[fred cook]

Late this afternoon I had time to drain the oil from the engine and pull the sump cover off of the block. Turns out that I had assembled it and the screen correctly. Don't know whether that is good or bad news! At least there are no pieces of the large green and red seals floating around! At this point, I am assuming that the oil pump seals and the oil cooler seals all went into place correctly. But, I still have the dropping oil pressure problem. While I had the oil out of the engine, I filtered it through a micro screen to see what might be circulating in the engine. Turns out that all I could find were some very small bits of the Loctite block sealer and of the Curil-T. I checked the bits with a magnet and got no takers. Nothing on the screen even began to look like aluminum. So, it appears that the engine bits are fairly happy with each other at this point. The car has only been driven about 2 miles since the rebuild, but any problems in break in running would have made at least some shavings.

Next I took a good look at a schematic of the oiling system. From what I could tell from the small drawing, the suction side of the oil pump picks up the oil and sends it to the oil filter and tank. from there, it drains back to the pressure side of the oil pump which sends the oil to the internal oil thermostat. From there the oil goes one route to the oil pressure light sender and pressure relief valve. In another channel, it sends pressurized oil to the crankshaft and cams. The crank and camshaft oil is then returned to the sump to be pumped back into the filter and oil tank. It occurred to me that since the pressurized oil has to go thru the internal oil thermostat, could the internal thermostat be causing this problem? If I remember correctly, it can only go into the block one way because of an offset of the holes the studs go thru. Also, at least in my case, the internal thermostat is one of the few things that has not been replaced in this engine. Any one else care to hazard a guess? At this point, I am fairly certain that this is a problem that should be "fixable" without breaking down the engine again!

Thks,

[fred cook]

Did not pull the piston squirters but did make certain that they were clear of debris. Same with the cam lines.