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

[fred cook]

Ok, I have checked the sump plate assembly (correct) and the oil pressure relief valve (works freely, no probs). Next step will be to pull the left side heat exchanger and the oil pressure safety valve. If something is blocking it even partially open that would explain the oil pressure drop. Once I get that done, I'll report back!

[fred cook]

Got this from GTIHOP in a PM.

Hey.
I have a thought about your oil pressure problem.
Are you running oil fed tensioners? If the valve on a tensioner had come apart or fell out on the right side of the engine where the oil pressure sender is located, it would definitely give you lower readings as there would be a unrestricted flow of oil leaking out of the tensioner. just a thought for something to check into.
take care and good luck

This could be a real possibility!

[fred cook]

I dropped the left side SSI today and removed the Oil Pressure Safety Valve. I was expecting to see some debris holding the valve open but, nothing! Everything in the valve appeared to be normal. I measured the depth to the bevel that the valve seats on and made certain that the valve cap went in that far. A picture with the bits out. Will finish putting it back together tomorrow and give it a try. If that doesn't straighten out the oil pressure, will take a look at the right side tensioner.

[KTL]

Fred,

The safety valve malfunction (stuck in normal resting position) would indicate excessive pressure, not low pressure. The safety valve activates when there is too much supply pressure created by the pressure side of the pump. The overpressured oil is dumped directly to the sump instead of being directed back to the inlet side of the pump. That is, assuming the right spring is being used. Too short of a spring and the safety valve kicks in sooner, limiting your oil pressure. But it's a high limit.

But if the safety valve activates and sticks, then the pump doesn't have to work to hold it in place. In that case, oil is still going to get picked up by the scavenge pump and sent back to the tank. But the pressure side of the pump is going to seek path of least resistance and pump to the sump instead of thru the more restrictive crank passages.

This diagram gives a simple indication of that



The diagram DOES NOT do a good job of helping you understand how the bypass valve works. I say that because the diagram makes it look like there is an intersection between the upward passage coming from the pump (below t-stat) and the passage leading to the bypass valve. You have to look closely at the diagram to see the way the lines are drawn- there is NOT an intersection there. They are separate/independent. This diagram is better.



The bypass valve kicks in at a lower pressure and allows oil to go back into the inlet side of the pump. Again, an issue with this valve would cause an overpressure problem, assuming the right spring is being used. Too short of a spring and the bypass kicks in sooner, limiting your oil pressure. Again, a high limit.

For either of those relief valves to cause your problem, they have to be stuck in a compressed position (high pressure had to occur at some point to move the pistons) then allow pressure to fall when they don't push against the pump flow and close their relief passages.

30465 lead the discussion on a very good pressure relief valve thread here

Ultimate Oil Pressure Relief Valve Thread

The internal t-stat should not be causing a pressure problem. It defaults to the cold position of course and sends oil on it's way to the crank via the upper passage in the color diagram. This passage contains the oil pressure warning light (ZERO oil pressure) and the bypass valve. From there it goes on to the crank. When the t-stat opens to the cooler, the cold passage in the engine case is closed (or partially closed depending on temperature/position) and oil goes thru the lower passage to enter oil cooler before returning to the aforementioned warning light & bypass passage and then on to the crank.

If the right side tensioner was having a problem, it would reduce indicated oil pressure since that is where the oil pressure reading is coming from. But wouldn't you also hear a chain slap noise? Insufficient chain tension does not go unnoticed. Sounds like a chain dragged across the rim of metal garbage can. I'm sure you'd freak out and turn your engine off right away if you heard that. You'd shut it off long before you built any temperature in the engine.

The cam line restrictors are arguable. They do reduce oil supply to the cam housings where it's needed most (besides the crank) to cool the rockers, springs and heads. However w/out the restrictors, the cracking/activation pressure of the piston squirters is high enough that they rarely get activated if you don't hit high rpms. So the cam restrictors do a better job of activating the piston jets which indirectly helps cool the heads via lower piston temperatures?

[Walt Fricke]

Fred - as you will have noted, it is pretty easy to shim the pressure springs. The pressure setting relief is easiest because you don't dump a bunch of oil each time you pull its plug. You might toss a couple of washers in there while installing it again, just to see if that makes any difference. If they do, that might rule out the safety relief spring.

For that matter, maybe purchase new springs for each. Not expensive, and probably easier than finding a spring checker for the ones you have. Which I assume are the right length.

[HawgRyder]

Fred...there are two different types of pressure valves...are you sure you have the right one?
Early (non-bypass style)...I believe is the one with holes in it...the later (bypass mod) has solid sides to the slider.
Bob

[fred cook]

Originally Posted by HawgRyder

Fred...there are two different types of pressure valves...are you sure you have the right one?
Early (non-bypass style)...I believe is the one with holes in it...the later (bypass mod) has solid sides to the slider.
Bob

Good thought, but yes these are the correct valves. When I disassembled the engine, the valve parts went into marked zip lock bags. At reassembly time, I used new springs from PP.

[fred cook]

At this point, I am going thru the engine checking (and eliminating) all of the external and semi-external possibilities. I am operating on the assumption that since the crank journals and throws all measured within standard ranges, that the engine had standard bearings when disassembled and that the new bearings were at least nominally thicker than the used ones, the oil pressure issues are not clearance related. The oil pressure in the original engine was good even when quite hot and I used the same block halves, crankshaft and oil pump. Also reused were the internal thermostat, oil pressure valve (new spring), oil pressure safety valve (new spring) and the tensioners. Also, when first started from cold, the oil pressures appear somewhat normal, dropping when the oil is simply warm but not hot. So far, I have eliminated from suspicion problems with the oil pressure relief valve, the oil pressure safety valve and the oil pressure gauge sender (replaced w/a new one). I have also verified that the sump plate and strainer were installed correctly. There are no external oil leaks visible. I have strained the oil thru a very fine strainer and only found "crumbs" from the block sealer. I checked the filtered debris with a magnet and nothing was picked up. None of the bits on the screen looked anything like aluminum. Based on what was and was not in the oil, it appears that the metal on metal surfaces are reasonably happy with each other at this point with no galling apparent at this point. This only leaves an unexpected bleeding off of oil pressure at some point. So, as I said earlier, I am going thru and checking and eliminating as many points on the oil circulation route as possible. While I did not really think the problem would be in the two oil pressure relief valves, they have now been manually checked and removed from the list of possibilities. As Sherlock Holmes (I believe) once observed, "Once all of the possibilities have been eliminated, what is left, however improbable, must be the solution". The quest goes on!

[Steve@Rennsport]

Which oil pump seals did you use??

[fred cook]

Originally Posted by Steve@Rennsport

Which oil pump seals did you use??

I used the seals that came in a master gasket and seal set from Pelican Parts. When assembling the engine, I noticed that each place the large oil passage seals were used that they seated properly and that there was a small amount of "springiness" between the parts as they went together indicating that they were being compressed properly. So far, I have not found any indication of a seal being cut during assembly. I've looked in both of the oil pressure openings and have pulled the sump plate to make certain it was assembled correctly (it was).

[Porshaah]

Originally Posted by fred cook

I am operating on the assumption that since the crank journals and throws all measured within standard ranges, that the engine had standard bearings when disassembled and that the new bearings were at least nominally thicker than the used ones, the oil pressure issues are not clearance related.

No clearance measurement/plastiguage performed before assembly of new bearings?

[fred cook]

Originally Posted by Porshaah

No clearance measurement/plastiguage performed before assembly of new bearings?

Yes, all main journals and rod throws checked with plastigauge. All measured in the middle of "normal". In the above post I was just emphasizing that there was no reason to suspect bearing clearance as the root problem. Since the oil pressure from a cold start appears to be in the normal range, but drops after the oil is warm but not hot seems to me to verify that the bearing clearances are ok. That is why I believe the problem to be elsewhere.

[KTL]

I don't recall if you checked your spring lengths. car311 did a rebuild not too long ago and his engine was in the good hands of a local Porsche tech. He too had a low-ish oil pressure problem and it turned out the bypass spring was a little short. Installed spring of right length and got the oil pressure he was expecting. Granted, his pressure issue was on the high end. He was only hitting 60psi and expected higher/same as before.

[nocarrier]

We had someone over in the turbo forum with an oil pressure problem right after a rebuild. It turned out to be the victor reinz seals used in the case. If I remember correctly, they measured significantly shorter than the elring or wrightwood brand seals.

[Lapkritis]

Originally Posted by nocarrier

We had someone over in the turbo forum with an oil pressure problem right after a rebuild. It turned out to be the victor reinz seals used in the case. If I remember correctly, they measured significantly shorter than the elring or wrightwood brand seals.

That would suck. I would write a nice letter to VR executive team for that one.

[Porshaah]

Originally Posted by fred cook

Yes, all main journals and rod throws checked with plastigauge. All measured in the middle of "normal".

That's reassuring. I'm not sure if it was this forum I read the new bearings received were thinner than the originals. Builder ended up reusing the old bearings.

[fred cook]

Originally Posted by Porshaah

That's reassuring. I'm not sure if it was this forum I read the new bearings received were thinner than the originals. Builder ended up reusing the old bearings.

I read that also. That is one reason that I measured the bearing thickness and compared the numbers to the measurements of the old bearings. The existing bearings were actually in very good shape, in a pinch I could have reused them. The only wear I could see on the old bearings was on the face of the thrust bearing and some wear on the oil pump bearings. I really believe that the problem will be found to be somewhere along the oil circulation system. Maybe something I did incorrectly, maybe a failed part. I will figure this out eventually!

[fred cook]

Originally Posted by KTL

I don't recall if you checked your spring lengths. car311 did a rebuild not too long ago and his engine was in the good hands of a local Porsche tech. He too had a low-ish oil pressure problem and it turned out the bypass spring was a little short. Installed spring of right length and got the oil pressure he was expecting. Granted, his pressure issue was on the high end. He was only hitting 60psi and expected higher/same as before.

I put in new springs on both the oil pressure safety valve and on the oil pressure relief valve. They were the same length as the old springs or perhaps a tiny bit longer. Good idea, though!

[fred cook]

Just finished putting oil back in the engine (after checking the oil safety valve) and letting it run (idle) for a while. After the engine had time to warm up a bit (about 2 minutes), I increased the engine speed to 4K rpms. Oil pressure at that engine speed was right at 2 bar(s). When taken back to idle, the gauge was showing about 1/2 bar of pressure. The engine is not making any unusual noises, not chain slap and nothing that could be considered to be rod knock, etc. I could not find anything wrong with the oil safety valve, valve slides easily in the bore and there was no trash visible. So, now I am about down to the end of the oil pressure gallery. The only things left to check are the two pressure fed chain tensioners. To access them, I will have to remove the rear engine support bar and rear engine tin. The only other thing that could be causing this low oil pressure might be the two block seals. If they did not seat properly or were not manufactured correctly then oil pressure could be being lost at the seal location. If that is the situation, then the oil must be leaking back into the case as there are no external leaks.

[JJ 911SC]

Seem you are half the pressure reading of what one to expect (1 Bar per 1K).

Do you have (probably) the right match between the Oil Pressure Sender and the gauge?

Did you replacement Senders was the same as the one that was fitted?