My article on the Oiling System of a Porsche 944 engine has been very popular on my website. I suspect that occurs mainly because folks have a problem with their 944 oil pressure and via a Google search they find their way to my article. You may have reached this article because you are experiencing problems with your Porsche. More on that follows below. Anyway, I have acquired a new candidate for reverse engineering, that being the oiling system on the M97 engine of my 2007 Cayman S.
Although my wife still owns the Cayman S she purchased in 2006, I value my marriage too much to use it as a research subject. But when I bought a 2007 Cayman S last year, an opportunity to reverse engineer its oiling system presented itself, when I decided to perform a full rebuild on its engine, as discussed here. While I had it torn down, I decided to educate myself on its oiling system. And yes, technically it is a lubrication system but oiling is just the way I think of it.
The engine on my 2007 Cayman S is 3.4 litres and is described by Porsche as a M97.21. My understanding is that this engine architecture is generically known as the M9x engine, as used in Boxsters and 911s from early in the water cooled era that began in the late 90’s. Whatever, what I am describing in this article is the engine from my 2007 Cayman S.
As proof that you can teach an old dog new tricks, this “article” includes a series of videos that I recorded and edited. Warning, the total running time of the 8 videos is about an hour. Wow, my first feature length film! With my understanding that the current thinking is that any video over 2 minutes is “too long”, many of you can opt out right now. But if you hang in there and watch the whole sequence, I promise you will learn a few things. But not about high level videography! Sorry about the very beginner nature of my filming.
As a general introduction, it has been said that the lubrication system of an engine is its “lifeblood”. Fair enough. Modern IC engines will not last long without lubrication. At a very high level, oil is collected in a sump at the bottom of the engine. An oil pump draws the oil from the sump and distributes it throughout the engine to those areas that require lubrication. The most common area that requires lubrication are the bearings, specifically shell type bearings. The shells encircle a “journal” that is rotating. The oil fills a narrow space (around 0.005″) between the journal and the bearing, providing a cushion between the moving and stationary surfaces. The most common examples are crankshaft main bearings, piston rod bearings, and camshaft bearings. Another type of lubrication is “splash” lubrication. A good example is the lubrication on the walls of the cylinders, where the rings on the pistons slide back and forth. So the primary function of the lubrication system is to provide an oil film between the moving metal parts, such that they don’t come into metal to metal contact and fuse together. The lubrication system also removes excess heat from the hottest areas of the engine. For instance, “piston squirters” spray oil on the bottom side of the hot pistons, serving to cool them. All of these functions are vital to the operation of a modern engine. Yet another function of the lubrication system is to provide pressurized oil for the hydraulic lifters, which serve as a dynamic “shim”. The lifters are a variable height device (shim) that direct the opening forces to the valves. Their primary function is to “pump up” under the hydraulic pressure of pressurized oil, dynamically filling the space between the rotating cam shaft lobes and the valves. They also require an oil film in their bores to keep them from seizing up. A similar function of the lubrication system on the Porsche engine is to provide oil pressure to mechanical devices that perform functions like adjusting valve timing (known as VarioCam) and to apply dynamic pressure to the timing chain tensioners. And of course the lubrication system requires a method to keep the oil clean, typically an oil filter. All of these functions are vital to the operation of a modern engine.
Finally, all of this needs to work from the Artic to the Equator, under acceleration, braking, and cornering loads, without input from the driver. With minimal friction and parisitic demand on the engine. It is really a fascinating technical challenge. Well, enough with the preamble. Below is a list of all the areas of the engine that require lubrication, in the rough order of the sequence that the oil flows to them. What is the value of this list to you? Remember, oil exits the oil pump at a certain pressure, typically ranging from 3 to 5 bar (~45 to 60 psi). Porsche engineers carefully balance what goes in to what goes out so that at the last device in the distribution pipeline, there is still enough oil pressure to do the job. If your problem is indeed low oil pressure, than it helps to understand all the items that might represent your problem. Troubleshooting can get really complicated in this regard but I’ll take a seat of the pants shot at some guidance, where I can.
Oil Sump- the lowest part of the engine. It is sealed with a large access plate held in by multiple bolts. The access plate covers the entire perimeter shown in the picture below. There is an oil drain plug in roughly the center. If your drain plug falls out or you have a big hole in your sump, that sir is an indicaton that you have a big problem!
Oil sump pickup tube- This short piece of “pipe” is made from plastic and is held in with two bolts. If it develops a crack or worse, the oil pump will suck air. Another bad thing! You can drop the sump access plate and see the pickup tube. Seeing a crack would be hard but it would be relatively easy to proactively replace this tube. Also shown in the picture are the scavage pump return pipes, discussed later.
Oil pump- As shown in the video, it resides on the lower front of the engine. Porsche oil pumps are very robust. I have no way of knowing but I suspect their failure rate is very low. I doubt that they “wear out” in any measureable sense. But I think they can be replaced without dropping the engine (I am told you need to remove the motor mount first) so that is always an option.
Oil Pressure Relief Valve- Built into the oil pump housing. As the name literally implies, it relieves high oil pressure. It has a passageway between the output and suction side of the oil pump. A metal plunger is held in place with a strong spring. When the oil pressure on the face of the plunger exerts a sufficient force over its cross section area, the spring compresses a bit, opening up a passageway that bleeds oil back to the suction side of the pump. I guess there is a scenario where the spring gets “weak” and the oil is bypassed at a lower than optimal pressure. Then there is a worse scenario where the spring collapses completely and the oil is bypassed continously. I can only speculate but I suspect Porsche designed the passage sizes so that this scenario does not cause the oil pressure to go to zero. Regardless, I think the spring and the plunger can be replaced externally without dropping the engine.
Intermediate Shaft Small End Bearing- the IMS has it’s infamous bearing subject to failure at the flywheel end of the shaft. At the other end is a more traditional sleeve type bearing, which is fed pressurized oil. The feed for this bearing is through a small slot immediately at the outlet of the oil pump.
Oil Filter- See the video for a discussion of the oil passageways built into the block but the first stop is the oil filter. As noted, the oil leaves the filter through the center post. A very obvious statement is that if the oil filter is leaking oil badly or the filter element is very very clogged, bad things will happen to your engine. It is very easy to remove the plastic cover and the filter element. Only a small amount of oil will run out i.e. you can change the filter without draining the oil from the sump.
Oil/Water Heat Exchanger- As shown in the video, a small silver rectangular element that sits on top of the block. It is a heat exchanger that transfers heat from the oil to the water/antifreeze coolant. There are several failure modes here. If the physical barrier between the water side and the oil side breaks down, you obviously have problems. The first sign of this on any car is “milk shake brown” oil. Normally you check the dipstick. Oh, snap, no dipstick on a M9x engine. I guess you need to drop your oil filter element. Also, the heat exchanger is sealed to the top of the block with 4 o-rings. If these start to leak, you have a minor problem. Unless it is just gushing oil, it soundn’t be a cause for the flat bed tow to the shop. It is technically external to the block and I suspect that it can be replaced without removing the engine but I don’t know for sure.
Crankshaft bearings- Finally, we get to the important stuff. There are 7 shell type bearings on the crankshaft. Each receives an oil feed through passages drilled in the crankshaft carrier. See video. As a general statement, shell type bearings are designed to wear as the mileage on the car piles up, as they are relatively soft compared to the crankshaft journals. They are technically an item that can be replaced, although to get to them requires a complete teardown of the engine. So to avoid repetition, when I talk about a shell or sleeve bearing, we have a location where pressurized oil exists on one side of the bearing and zero pressure oil exists on the other side. When the engine is running, the oil goes from the high pressure side to the zero pressure side at a rate that can be calculated using equations that take into account the bearing clearance, the bearing area, the oil pressure, and the oil viscosity, to mention the main terms. On a “worn out” engine, the bearing clearances have grown larger over time and allow the bearing to pass oil at too high of a rate. This lowers the overall system pressure of the oil. In general, this effect should be gradual over time. A sudden failure of a bearing usually results in a loud knocking noise from your engine and possibly a sharp dropoff in pressure. Evaluating noises can be tricky but if your oil pressure light goes on and you hear a new knocking noise, shut the engine down immediately and call for the flatbed! If you hear a new knocking noise without an oil pressure light, the noise may or may not be significant. A flatbed to your shop would be the conservative move. A low rpm limp home might be an alternative. Not all new noises are fatal but you just never know!
Rod Bearings- We typically refer to the “big end” connecting rod bearings as they are physically larger and attach to the crankshaft. These are shell type bearings. At the “small end” of the connecting rod is the piston pin, which obviously connects the rod to the piston. These are sleeve bearings but do not have any pressurized oil feed. The situation with the big end bearings is the same as for the crankshaft bearings. Wear can cause oil pressure loss. Failure in many cases does very bad things to the engine. As discussed in the video, the big end rod bearings are supplied oil via internal passageways drilled in the crankshaft. They take their “feed” from the mainshaft bearings.
Piston Squirters- These are built into the crankshaft carrier. See video. Their openings are small but I also read somewhere that they spray a significant amount of oil, which means they are a main contributor with regard to the oil pressure situation in the engine. I think they are more at risk of getting clogged than wearing too large.
Crankshaft Carrier/Block Oil Passageways- This could be a little bit of a sleeper issue. Watch the video to see what I am talking about. I was surprised to find no evidence of factory sealant around these passageways. They seem to rely on a very good set of machined surfaces on both the crankshaft carrier and the block to provide a seal. I could envision a scenario where there might be some weepage or worse at this surface, resulting in an undiagnosed pressure loss. Upon teardown, I would look carefully for any discoloration at this interface that might be indicative of a leak path. That said, my engine looked fine in this regard.
Next we move onto the cylilnder heads. You really need to watch the video to understand what is going on up there. There are clearly two cylinder heads, in the M9x world known at Bank 1 and Bank 2. The lubrication issues are identical, with the exception that oil pressure sending unit is on the bank 1 side.
Camshaft bearings- These are a sleeve type bearing. There are 3 per camshaft or a total of 6 on each cylinder head. Porsche clearly does not plan for these to wear, as there is no bearing shells to replace.
Exhaust Valve Lifters- These are as described in the introductory remarks and in the video. There are two exhaust valves per cylinder so there are 6 exhaust valve lifters per cylinder head. If the lifter fails, typically referred to as “collapsing,” you will hear a sharp rapping noise. Diagnosing engine noises is an aquired art but if your oil pressure is generically low you might hear multiple lifters. This can also occur upon initial startup of a fresh engine rebuild or an engine that has not been started in a long while.
Intake Valve Lifters- These are as described in the introductory remarks and in the video. There are two intake valves per cylinder so there are 6 intake valve lifters per cylinder head. Just like the exhaust valve lifters, if the lifter fails, typically referred to as “collapsing,” you will hear a sharp rapping noise. To complicate things further, these are a more complicated lifter if your engine has Variocam +. Which is also why they cost so much!
Variocam- Porsches trade name for variable timing on the intake valves. As discussed in the video, the actuator for this system uses pressurized oil. If it fails, I would suspect that Porsche designed it to “fail safe” but I don’t know. You can use a PIWIS or a Durametric diagnostic device to determine if this system is working correctly. BTW there are two components in play here. There is what I think is strangely called the Throttle Control Element, which looks to be an electro-mechanical switch for sending pressurized oil to the Variocam. And there is the actual Variocom actuator on the end of the camshaft. Both can theoretically be accessed without dropping the engine. I say theoretically purely because based on just replacing spark plug coil packs, access is very limited in there.
Variocam +- Porsches trade name for variable lift on the intake valves. As discussed in the video, this system uses pressurized oil to change the “state” of the lifters from low lift to high lift. If it fails, I would suspect that Porsche designed it to “fail safe” but I don’t know. You can use a PIWIS or a Durametric to determine if this system is working correctly. BTW similar to the Variocam there is a Throttle Control Element, which looks to be an electro-mechanical device to switch pressurized oil from the low lift to high lift state. As with the other Variocam parts, they can theoretically be accessed without dropping the engine.
For both the Variocam and the Variocam +, I assume you would experience a noticable drop-off in engine performance if either failed. I also suspect you would get a dash light. I would not expect them to set the low oil pressure light on but I do not know for sure about this.
Chain Tensioners- There are several devices that serve to provide the correct tension of the various timing chains. They are supplied presurrized oil. If they fail or collapse, you would immediately get bad noises.
Scavage Pumps- As discussed in the video, there are oil scavage pumps at the end of each exhaust cam shaft. These help to move zero pressure oil that collects in the heads back “uphill” to the main sump. I think they are pretty bullet proof. In the unlikely event of their failing, you would not get a low oil pressure light. You might hear some bad noises. As discussed in the video, for an engine on level ground with no lateral g forces, there is a path for the oil to drain back by gravity, even if the scavage pumps are inoperable.
Scavage Pump Return Tubes- I not sure what they are officially called but as discussed in the video, in the sump there are two plastic tubes that scientifically dump the oil returned from the heads into the sump in the most advantageous manner. What I mean is that they are rumored to have a “de-areation” function. Their cracking or outright failure of one of these tubes (there are 2) would not obviously in my mind create an immediate issue such as a low oil pressure light.
Oil Pressure Sending Unit- This is screwed into the cylinder head cover on the Bank 1 side only. It is a simple on/off switch. If the pressure falls below its “setpoint”, it will change state and set the oil pressure light on your dashboard. It does not measure actual oil pressure per say, although I understand folks who want to data log their oil pressure have come up with alternate devices that allow them to do so. Just keep in mind that this measurement point is way out at the end of the “supply chain” so to speak. That is conservative but bear in mind that low oil pressure at the sensor may not necessarily equate to low oil pressure throughout the entire system.
Oil Level Measurement Device- See video. It is not part of the pressurized lubrication system but clearly serves a critical function. I have not determine yet how hard it be to remove it through the engine access opening.
Whew! So that is quite a list of things that need/use oil from the lubrication system. Problems with any of these will result in various levels of havoc with your engine. With the assumption that there are some DIY folks reading this, I’m going to provide a few big picture checks that you can make. This is just one car guy talking to another so if things go wrong for you, don’t come after me!
Oil Light Illuminated On Your Dashboard
OK, that is always a pucker up moment! I hope you shut your engine down and evaluated your options carefully before proceeding.
1. If it just flickered, it might just be a low oil level in your sump. The frustrating thing is you have to wait many minutes before you can get a reading. I guess this is to let the oil drain back to the sump. We had this happen on my wife’s car right after we went through a car wash. We moved the car to a nearby safe location and called a cab. I came back the next day. No light. You never know!
2. Is the light giving you a false positive? Another way of saying that something has failed in the sensing circuit that is making the light come on even though the pressure is fine. There are a lot of failure modes here and I don’t feel qualified to get into details. I would certainly try and access the electrical connector for the sending unit and do a few basic tests. I may have to swing back around to that with a future article.
3. Something has truely failed. OK, this one requires a little courage but no guts no glory. Remove your oil filter housing and the filter element. If possible, remove the fuse to the fuel pump. Have a friend crank the engine and see if oil does or does not gush out of the filter base. Use your judgement but 5 seconds of cranking should prove the point. Of course there will be a mess but I don’t think short bursts of cranking will hurt your engine. Just don’t get carried away. An option is to remove the sending unit and check the oil flow or lack thereoff from there. Or do both to bracket the situation. BTW, on the 944 engine, “lack of prime” is a common problem. This means the oil pump cannot bring up oil from the sump level to the level of the pump suction intake. This is typically caused by a crack in the oil pickup tube or by a loss of seal at the crankshaft carrier oil passageways. When I look at my M97 engine, the cracked pickup tube is a distinct possability. They are cheap so if there is any doubt just replace it. The passageway to the inlet of the oil pump is a solid cast channel so the only other thing I could think of is if your oil pump looses its seal at the forward face of the block. Some people introduce modest oil pressure to their dipstick to force the oil to prime. Oh wait, scratch that option 😦 But you can probably think of similar ways to temporily pressurize the oil sump. Don’t go crazy. No more than 10 psi!
Low Oil Pressure
Well, as discussed you have no way of really knowing unless you swap in an alternate gauge or sending unit at the cylinder head cover port. Regardless, if you have followed with me to this point, maybe I have generated some ideas on how to proceed. Unfortunatly, your diagnosis “decision tree” has many branches.
Bad Oil Leaks
I like to call them “gushers”. Again, if you have followed with me to this point, maybe I have generated some ideas as to where to look.
OK, is that enough words? Sorry, that is what I did for a living for 45 years. It just comes naturally. Anyway, I will conclude with a “flow diagram” and links to the video series. You do not need to Like me or Subscribe, I am not doing this for profit or fame. If you like what you see, a short note of appreciation is always welcome! Click on the Contact button.
Porsche M97 Engine Lubrication System Flow Diagram
As you can see, this is my sketch, not a Porsche document. I feel confident about the general flow path shown. That said, my understanding of the “stealth oil passages”, especially to the heads using the cylinder head bolts, continues to evolve. Use at your own risk.
If you have gotten this far, congratulations. There is no reward but hopefully you learned something.
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