964 low oil pressure solved, new question
 

Back at the end of August, while driving my 1990 C4 w/113k and no known engine work, the low oil pressure idiot light came on at a stop light and the pressure gage indicated a lower reading than normal. In the weeks the followed, I replaced the oil pressure sender, changed the oil, had the oil analyzed, and then pulled the pressure relieve valve plug/spring/piston assembly which controls the oil pressure. The piston was in good shape as was the spring and so I reassembled and poured the oil which had drained out while examining the assembly into a spent oil container. In the bottom of the pan I found a small ball of metal (~3/32") which appears to be brass, but which is slightly magnetic (ferrous).

http://forums.pelicanparts.com/uploa...1160488720.jpg

The oil analysis did not show any abnormal results with the exception of 25ppm copper vs. the expected average of 11ppm. Once the oil relief valve was replaced, the oil pressure problem was solved. I am relieved that I was lucky to have a simple fix for a possibly major problem, but I am still concerned. I plan on having another oil analysis done in about 3k miles to check for any trends.

My primary question is what inside of the engine might contribute to forming this metal ball and was it formed at the end of the oil relief piston or is that just where is finally lodged? Does someone have a picture or drawing of how the relief piston works?

--tom

First thing that pops into my head is piston oil squirter check valve.

Are those present in the 964 3.6 engine? If so, are they a steel ball bearing? What diameter? Where did the brass come from?

Anything which could be monitored or checked in order to try to determine if this is the case? I can do some further analysis on the metal ball to see if the core is something different...

--tnx
--tom

yes,
http://forums.pelicanparts.com/uploa...1160652165.jpg
http://forums.pelicanparts.com/uploa...1160652199.jpg
http://forums.pelicanparts.com/uploa...1160652227.jpg
these are for a 993 but in the area where the squirters are the 964 and 993 are the same

there is a small round check ball inside of the cylindrical squirter body

Thanks for the diagram, but the 964 is slightly different in that it only has one oil filter. I cannot seem to find a similar diagram in my 964 service manual, at least not in the obvious place, and Adrian's book doesn't seem to have a diagram at the level of detail of your 993 illustration, so I'm guessing a bit...

In the single oil filter 964 system, does the oil flow though the filter on the way to the engine or on the way back from the engine? If it is on the way back, then the object could reach the pump and pressure relief valve straight from the tank.

If the object was from the piston squirter as you have suggested may be possible, wouldn't it have to pass through the screen on the oil pump? What is the hole size in that mesh?

--tnx
--tom

The 964 just connects internally where the 993 engine mounted filter console is, it makes no difference as far as your ? goes.

If a squirter pops out it goes directly to the sump. see the squirters in the crankcase pic?

Unfortunately Bills estimation is the same as mine, the piston squirter is the only place I know of that would have a ball like that... It would also explain the higher copper content too, becuause when a squirter goes, the oiling to that main bearing drops dramatically and would wear out that bearing.. (Hence showing/leaving copper)

So the current thinking is that it is probably time for a rebuild?
What kind of risk am I taking by continuing to drive in the current condition (e.g. how soon do I need to do the rebuild)?

Sorry if the following questions about rebuild options have already been answered elsewhere, please forgive me...

Assuming that I am fully capable of doing a large amount of work myself, but there is a question of time vs. money, and that the car needs some other attention (e.g. front gearbox axle seals are beginning to weep, etc.). What are the rough price differences in these options:

1. Should I just drop the car at Stoddards (about 3 hours east of me) and have them do what they feel is needed.
2. Drop the engine myself and ship it to Stoddards (or other suggested/reputable rebuilder) and then replace it when it returns.
3. Drop the engine and do the rebuild myself?

--tnx
--tom

Hi,

If what Bill and Chris is true I'd try to get hold of an old squirter (if possible, otherwise buy one) then open it to see what the ball looks like and if it's magnetic as you mentioned the 'item' is. If that matches up then the story is known. No idea though if those squirters have changed over the years nor if they are prone to failure.

Wonder if the oil pressure, at some point in time, could have gotten to high so that the ball was pushed out from it's location (or would it have to be sucked out) ?

Michael

Hi,

Long shot, but if you took out an oil return tube can you then inspect the piston squirters with a borescope ?

Michael

Tom,
I'm going to have my 3.6 case back from the machine shop in a week or so. I can take a look at the squirter to see if I can confirm that they are magnetic and what they look like.

I think the answer to your question has to do with for how long you can live with the car down.

I would guess option #1 would = $15k with all the ancillary items included (resealing the tranny).
2. You might shave several thousand $s from the bill. You might even look at sending the engine to one of our resident experts on the board (Steve Weiner comes to mind), shipping is expensive, but I bet he'd do a far better job than a dealership. Joel Reiser is close to you, too and is in the same boat.
3. you could probably do it for $5k to $8k, depending upon what you have done, if you seek more power, new cams, porting.
4. might be a good option, especially if you want to rebuild yours. You could buy a replacement (get a running one that you can test and document. Probably worth $6k to $8k. Rebuild yours and sell the spare when you are ready.

I've had my car down for the better part of a year, when I thought I would do a simple swap and be done with it in three months. My story is unique on one hand, but as it turns out not so unusal :D :D

Just one man's opinion.

Doug

Thanks Doug!

Tom- If you want to think about option 3, note that Bruce Anderson and Jerry Woods are giving their engine rebuild school this December. I won't be at that one, but may take Transmission again a couple of days after engine.

Also you are welcome to do option 2 & 3 right here with me this winter, if the distance isn't a problem... I am another 3-4 hours east of Stoddard. jmreiser@frontiernet.net

Not sure how I shoud take that:confused:

heh heh. Unfortunate for him is what I meant Bill. You're not getting sensitive are you. :p

I think it's a great idea to try and tear apart an old squirter and see if it matches... I don't know if you can get a borocope bent properly to look, but I know I'd try.

I don't think you'll get many more miles out of the engine before something bad happends if this is really the case... I hope it's NOT!

Hi,

Even if the borescope can't bend to see the squirter you could add a little mirror on the end. I'm quite sure that would be possible and the cost of a oil return line is peanuts in the engine build comparison. One guy at work have this model;

http://www.uniqueproductsonline.com/opticscope.html

Quite good and I think with a dentist mirror you would be able to see something.

Michael

Makre sure you get one with a light.

Does anyone have a 964 case they could work out the angles from the oil-reurn tube hole and a piece of wire?

I've been reading this thread with interest and confusion. Are the balls in the squirters:
-a check valve to eliminate back pressure?
-a valve that allows oil flow through the squirter above a certain pressure?
-an object to shape the spray?

If they are a check valve, then the sprayer is probably still working as intended cooling and lubing the back of the pistons. However, is there a risk of damage to the oil cooling system from the pressure?

If they are a pressure relief, then they are still happily spraying the pistons, but at all pressures, not just above the valve's limit. No so bad either, unless the open valve lowers oil pressure somewhere else in the system causing wear.

Lastly, if the ball shapes the spray, then there is a chance the spray is not hitting the underside of the piston as designed lessening the cooling effect?

Now I'm wondering if in addition to the ball missing, the shape of the squirter after the ball was forced through it is also an issue. Either way it needs repair. Wayne's rebuild book explains that the squirters were implemented by Porsche in 1970 to reduce piston head cooling by a significant 100 degrees. These engines need cool pistons to survive the stress we put them under!

Here’s another quandary… Where’s the spring that holds the ball in the squirter? I’m guessing is stuck in the pump screen!

Out of curiosity, I'm going to visit Kelly Moss Racing to see if they have one laying about that is either disassembled, or I can hack open!

Don,
I'm no expert, but I've learned a bit recently.

The check valves are shut below a threshold pressure. So the pistons do not receive cooling oil at idle. I believe they open above 3.5 bars. That figure was provided by Steve Weiner off of the top of his head. In a 964 engine, the factory spec says 2.0 to 2.5 bars oil pressure at idle and above 5. bars at 2500 rpm. As was already stated, seems like it would bleed pressure if the ball is missing.

Good thoughts on questioning the shape of the resulting spray.

Doug

Don,

The balls are a check valve. The sprayer stays closed untill a certain pressure. i thought it was 30 psi (2 bar)but it may be 3 bar....

Okay, so the ball is part of a check valve system as suspected. Check valves are used to keep fluids from returning backwards through them. So I guess Tom, the author of this thread may have a squirter that squirts the back-side of the piston and lubes the wrist pin bearing. It works at high bar\psi but also at low pressures. That doesn't seem all too bad to me. I'm still at a loss as to why Porsche used a check valve in the squirter.

Don, Unfortunately it is my thread and I am the one with the engine in question. I guess the term "check valve" is a bit of a misnomer as it is really a pressure regulator that does not allow the squirter to operate until there is enough pressure to open the valve. As I understand it, the squirter's purpose is primarily to reduce the operating temperature of the dome of the piston up which it squirts (by 100 degrees or so). If the pressure regulation ball in the squirter comes out, then presumably the squirter is operating all of the time rather than just when the pressure is above 3 bar (off idle). So if the remaining "nozzle" which the squirter fell out of is still able to hit the back of the piston with oil, then the cooling effect should still be present, however as the pressure regulation is no longer pressent, other areas of the system may be starved for oil (e.g. main bearings?), particularly during idle conditions. Sigh...

--tom

Thanks for the information. I've always had a sneaky suspicion that some of my squirters were malfunctioning as they were way easier to clean than all the instructions on Pelican suggest. Maybe I have the same problem and will be pulling my engine just like you. Three of the squirters are on the same oil line as the main bearings so trouble looms. Anyway, I didn't mean to hijack your thread on this fantastic public forum. Sorry!

Is there any update on this engine problem?

-Eric
90 C2

I swapped in a '92 engine and the '90 is sitting in the front of my garage waiting for me to decide what to do with it. I won't know if the metal fragment was from a squirter or somewhere else without either opening the case myself or sending it out for a rebuild.

maybe it's a plug from a crankshaft oil passage.

I wish that I had more knowledge or a better diagram of the oil flow for a 964 so that I could better speculate without disassembly. The metal bead was found in the pressure regulator which as I understand is after the pump, which is after the screen. So unless a larger than normal hole developed in the screen, how would anything this size from inside of the case end up where it did?

It could have fallen into the tank.............

-Eric
90 C2

Tom,
The 964 diagram looks very much like the 993 posted by Bill Verburg. However, the oil filter, fed by the outlet of the oil pump does not exist.

Also the bridges (to feed the top end) are smaller in size since the 964 uses a solid lifter cam, where the 993 uses hydraulic lifters.

Doug

I can send you a ball from a squirter assembly if that'll help... Just PM me.

Sorry if I'm asking a stupid question here, but I would just like to be clear. the pump draws from both the tank and the sump, passes through the pressure relief valve, then to the engine's oil ways. If the metal object fell into the tank or was a loose scrap from the brazing of the tank, etc. it would just pass through the pump and end up in the relief valve, never having to go through the sump screen. This sounds likely.

Right, the 2nd oil filter does not exist on the 964, so that oil flow is non-existent.

Thanks for the offer Don, but I'm not sure that it would help. Do you have a picture of the squirter assembly? That would be interesting to see...

That would be my thought as well.

But wouldn't a plug from the crankshaft oil passage have to flow through the oil pump screen in order to arrive at the pressure relief valve? I believe that the hole size on the screen is smaller than the size of the metal bead.

Tom,
The oil pump is really two pumps sharing a driveshaft. One pumps clean oil gravity fed from the oil tank to feed the lubrication system, which includes bearings, cams and moving parts.

The second is to scavenge oil from the crankcase and send it out to the oil cooling system and on to be filtered prior to re-filling the tank.

Doug

Going back to your original photo, the ball from the squirter looks too small to be your stray part. Attached is a photo of a dime and a disassembled squirter (sorry, the camera doesn't have a zoom).

Could the stray part be part of the oil pressure sender you replaced? If I had one, I'd probably cut it in half just for fun...

http://forums.pelicanparts.com/uploa...1179196782.jpg

Oil flow diagram for engines with on engine cooler, should be same as 964

http://forums.pelicanparts.com/uploa...1179328495.jpg

Fred