Part TWO

By Tim Wright

Understanding the Lubrication Needs of SHOs.
Part 2 - Paths & Flow Designs

Below is an illustration of the V8 SHO lubrication system from the 97 Helms. It is actually rather simple.

The oil pump pickup (5) is submersed in the oil pan sump. The pickup has a mesh screen to protect the pump from the largest chunks of debris just in case a piece of piston skirt could chip off or some other semi-catastrophe. The (7) positive displacement internal gear "G pump" in the V6 is capable of 12.1 GPM at 6400 engine rpm and the V8 pump is of similar design and rating.

The oil pump is located at front of the engine, which is the passenger side of the car. The center of the pump is driven off of the crankshaft snout. Oil pressure in excess of 55 psi opens the (6) relief valve preventing damage to the up-stream oil filter. Cold oil or high viscosity oil can dump out here, a good reasons to avoid heavy motor oils or stressing engines when cold because oil that never gets to the bearings can not protect them in any way.

Before the oil gets to the filter it passes through the heat exchanger or (3) engine oil cooler. Both oil and engine coolant pass through this shared canister bringing them closer to the same temperature. Because it is a fluid to fluid heat exchanger as opposed to a liquid to air radiator it is very compact and efficient. All engines depend on oil as a coolant to some degree, the SHO much more than most, except perhaps for air-cooled engines. Oil to coolant heat exchangers are most unusual on production street cars and evidence the importance of keeping the viscosity light to maximize the quantity of heat removed by oil. Oil works best over a narrow temperature range of 220 F to 260 F degrees. Above 285 F conventional motor oil oxidizes and begins to turn to varnish. Below 220 F oil is still too cool and too thick to provide optimal lubrication. The heat exchanger keeps the engine oil in the narrow optimal temperature range.

Next in line is the screw on (4) oil filter. The annular ring of the cylindrical filter receives the "dirty" oil and under pressure infiltrates to the core which is the "clean" side of the filter. When excessive pressure exists across the filter medium a bypass valve opens permitting dirty oil to by-pass the filter medium preventing oil starvation at the bearings. Some oil filters have the by pass on top near the inlet (as illustrated), other designs have the by pass on the far end of the element or the bottom.

This design does not meet Ford standards for three reasons. With dirt and metal chips collecting on the far end of the filter if the by pass valve is located down there it will be swept up when the bypass valve immediately above it opens. Oil coming from the engine washes over the dirty side of the filter media when the bottom by pass valve is open. A top bypass oil filter passes unfiltered oil to the engine but a bottom bypass filter washes dirt off the filter add it to the dirt load in the unfiltered oil and hits the bearings with a much greater amount of debris - at least in theory! The last strike against bottom bypass filters is the problem with ice. In theory, the dome end of the oil filter should be the lowest point of the lubrication system and it work as a place to collect excess moisture and water. If water was in the bottom of the filter and froze it could either obstruct or freeze the bypass valve closed. The PureOne by Purolator has a bottom bypass valve, but the Motorcraft, made my Purolator for Ford has a top bypass valve. I don't want to get in Dutch with either design camp and will try to get some balancing information from Purolator and Amsoil.

Pennzoil Technical Information

June, 1999

Over-Pressurized Lube Oil Filters

Technical Services

Oil by-pass occurs when the engine and oil are cold, or when the viscosity is too high, or when the filter medium is loaded up and can not filter oil as quickly as it is being feed. The important point we will return to latter is the difficult job of filtering out sub 10 micron size dirt particles while maintaining a flow of many GPM of oil. Even when the oil and engine are warm achieving this using any device no bigger than a coke can in next to impossible because the filtering area just does not fit in shell that small. If we knew when the bypass valve was open we may take it easy longer when the engine was cold. Depending on the filter it may also be true that we are in full bypass mode anytime the engine is running over 3000 rpm and the secondaries are open - even with a warm motor and clean oil! Some filter designers trade flow capacity for the ability to clean the smallest dirt and have bypass valves that open at lower pressure. Others make the opposite trade off, they flow higher quantity and don't clean as well on one pass, may have higher opening setting for the bypass valve and rely on their multiple pass efficiency to filter out all the dirt. In the small space provided it is impossible to make a single filter that flows 12 GPM and cleans 100% of the oil down to the smallest size. It is possible using premium filter medium and clever design to do an acceptable job but we will come back to that later. Some race cars avoid this problem by running two very large truck size oil filters in parallel. You can too if you don't mind moving the battery. They good news is you may not have to. In race cars the goal is to contain all debris if the engine has a sudden major failure. With most street engines we need only keep up with dirt and minor engine wear.

The SAE "Life and Efficiency" standards require oil filter shells to be capable of withstanding 200 psi of pressure. Why when the pump only generates 55 psi? When the oil is cold it is very difficult to filter. Sub SHO quality oil filters can do many strange things in use. They sometimes explode or rupture. Recent offshore manufactured AC Delco PF35L oil filters have a reputation for that. They also implode - the pressure differential can collapse the center tubes into a crushed shape like a submarine at the bottom of the sea. Once damaged on the inside the element can detach on the inside so you have an empty shell doing nothing with the element bouncing around inside the can like a baby rattle. The high pressure turbulence of hot incoming oil will knock it around inside the shell like a tennis ball and it may further self-destruct. Pennzoil and to a lesser extent Quaker State have PDF files on their web sites "diagnosing" bad engine relief valves for batch of oil filters with collapsed guts and ruptured cans. I guess they don't have internal bypass valves that work or their typical buyer uses thicker weight oil in their motors. They say their filters are OK to 150 PSI, normal pressure is 30-60 PSI, why not 200 PSI as required by SAE tests? In time the heat cycling a filter endures can enbrittle the paper media which can deteriorate like a wet newspaper in a hurricane littering the engine with little bits of paper on bearings surfaces, cam lobes oil galleries and blocking off the oil pick up screen starving the oil pump. Running high viscosity motor oil increases the pressure difference; making filter damage that much more likely but why risk a bargain filter when the combination is a recipe for problems?

With every stroke an engine inhales some small amount of dirt that is too small to be trapped by the air filter. A larger amount of oil filtering media can pass more oil at lower pressure than a smaller area of the same quality. But just as important it can also store more dirt. As pores in the media plug up other pores come into play until all the pores are plugged up and the oil must use the bypass valve and the oil filter should be replaced. Instead of thinking of cleaning efficiency one can also think of filters as "3000 mile" trash cans and when or if the trash can is full the trash overflow will bypass as unfiltered and eats engine bearings and cam lobes. A filter with more square inches of filter media not only flows more oil at a lower pressure but also has a proportionally higher capacity to hold dirt - which buys running time. If you are behind a soot belching municipal bus or filthy dirt covered construction truck and the airborne particulates inhaled by your engine may momentarily increase 100,000 fold it is a great thing to have a disposable place to be rid of dust and carbon soot.

One common design combination known not to work is thin shell, cardboard end caps, a small amount of high efficiency filtering media and heavy viscosity cold oil. The cold thick oil can not pass the filter so the thin can bulges or explodes and the guts of the filter may be crushed. Every time we change oil we pour in 6 quarts of stone cold oil and jazz the pedal we play Russian Roulette with our bearings. Many cheap filters "let it rip" while they are still on the lift, - at the dealership.

Before oil leaves the filter, a one-way anti drain back valve keeps dirty oil from returning toward the engine from the filter when the engine is shut down. This can not happen on the V8 SHO because of its vertical mounting but it does on the V6. Oil leaving the filter passes through the (3) heat exchanger a second time and this is where the oil pressure send unit is located.

Once the oil is back in the block Ford does an interesting thing. All exits are in parallel, not in series. Almost all of the oil can either head to the main bearings or cam bearings but not both. It is like a controlled leakage situation with all the paths short and each path quantity exactingly controlled by clearances. If it routes to the cam bearings it lubricates and cools those bearings and the (1) Timing Chain Sprocket Tensioner then splashes the valve shims and drips home. Oil sent to the main crankshaft bearings lubricates them then travels to the rod bearings via holes drilled in the "cross drilled" crankshaft. After the rod bearings the oil travels the length of the connecting rod and lubricates the wrist pin and finally returns to the oil pan via the oil control grooves in the piston. Did I almost forget to mention, a small bit of oil is also sent to the (8) Front Chain Tensioner?

A subtle game is at play here balancing the clearances of the diverse paths to balance oil flow. If for example, one were to replace the factory pistons with ones that have a lose fit, more of the oil would take the easy path to the detriment of oil flow to the cam bearings. The factory system is very reliable if we just do our part, use quality oil and oil filters.

One final thought:

Oil coolers are not radiators; they are oil to air heat exchangers. In order to function they must be supplied with large amounts of the coolest air possible. This means ducting and it means that oil coolers should not be mounted in the exit ducts from the water radiators-no matter how convenient it may be. One last word-in cases where the designer fell off his drafting stool and has provided a totally inadequate water cooling system, it may be possible to drag the water temperature down by super cooling with oil. - "Prepare to Win" Carroll Smith, Aero Publishers 1975.

Now in this context Mr. Carroll Smith is talking about oil coolers that look like radiators not fluid to fluid heat exchangers like the SHO has. With the exchanger the oil and coolant will tend toward the same temperature. But when is the oil heating and when is it oil cooling the coolant? One would need an oil temperature and a coolant temperature gage to know for sure. I would like to know! I think oil would achieve operating temperature first, heating the coolant and speeding up the process of engine warm up. If the radiator is sized large enough the coolant should tend toward the same temperature or a little warmer than the thermostat setting. Is the coolant ever warmer than engine oil? I don't think so. I am again speculating that creating water jackets in the SHO heads close to those double exhaust valves with good flow is no simple task when the same area is at a premium for the double exhaust port passages. A problem further compounded by the high specific engine output and compact design of the engine. I suspect the plan here was that the high quantity of oil bathing the heads washes away heat from hot spots the engine coolant does not have the best access to. Just another reason to be very particular about oil, oil filters, and maintenance intervals with a SHO. Knowing what I do about the Yamaha engineering I doubt anyone fell off his drafting stool. I doubt they still have drafting stools to fall off of. But ol' Carroll is right about one thing "it may be possible to drag the water temperature down by super cooling with oil."

You mentioned in one of the parts about the relationship between water and oil temp. I have digital gauges in the race car with 1F calibrated sensors, one in the coolant manifold, the oil temp sensor is located in the main galley above the crankshaft, right above the passage going down to the rear main bearing. (This sensor is only accessible when the flywheel is off...) Once the engine is warmed up, oil and water temps track within a few degrees for light driving and highway cruise. Only when loading is high does the oil temp exceed the water. On the track, I see 220F coolant and 230 to 240F oil temps. At cold start, the water also warms faster than the oil, I see the coolant temp start to rise from ambient within 5 seconds of cold starting the engine, were-as the oil lags by several minutes during the warm-up phase.
There is also a rather ingenious bypass valve in the core of the oil/water heat exchanger. Its not thermostatic, but is viscosity based; If the oil is viscous (cold...), it will bypass the cooler and go straight to the engine. It's a simple spring-loaded plunger that opens and allows oil to bypass the cooler. Don't know if this gadget is on the V8 oil cooler, but it is on the V6. The V6 routes the oil through the filter, then through the cooler. This may also help protect the cooler from overpressure spikes seen at cold startup. - Gary Morrell

This is interesting in that on cold start the oil cooler may actually work as an oil preheater and aid engine warm up, minimize start up engine wear and perhaps effect start-up emissions.

Rambling Oil Filter thoughts.

LOWERS ENGINE TEMPERATURE OFTEN 20°F OR MORE
The Airwolf Remote Oil Filter System and its hardware are a natural conductor of heat. That is why we affectionately call it the "poor man's oil cooler". A properly installed Airwolf Remote Oil Filter System with ample air circulation can help reduce your engine oil temperature significantly. (from Airwolf web site)

This is an indication of the ability of an air stream over a remote filter system to remove heat. Fluid to fluid coolers can be 1000 times more effective than air to fluid radiators because of the density of fluid and latent heat caring capacity per weight. I think we can assume that the SHO oil cooler can remove a LOT of heat from the oil. Maybe in an airplane a remote filter may remove a lot of heat but I suspect the cooling ability of a remote filter under the hood of a car to be subtle, nothing like 20°F

On magnets, note that SHO engines also have little to no ferrous metal in their construction. The block of the V6 is iron but the V8 is all aluminum - heads and block.

What do you think of these "super magnets" that attach to the outside of the oil filter?
First of all you have to realize, that there is very little ferrous metal in an aircraft engine. However if you wanted to collect what little there is, it really is not very efficient trying to accomplish it at the oil filter location The oil is typically traveling at over 7 gpm as it goes through the oil filter. These Neodymium " super magnets" as they are commonly called, are really not so super or strong enough to pull this ferrous metal out of suspension as it whizzes by at 7 gpm. It just isn't possible. In addition, most people don't realize that Neodymium magnets loose their magnetic properties the higher the temperature gets, where at 200°F they have but 10% of the magnetic forces left. Guess what your engine operates at. 185°F. If you really wanted to put a magnet into your system, the ideal place would be the bottom of your drain plug. This way what little metal you may have suspended in your oil, is allowed to slowly fall out of suspension to the bottom of your oil pan, where it slowly migrates over to the lowest point in your sump, where it could be collected by a simple magnet. Just like automobile engines have done for years.

But then Glen came through with this helpful note. It seems even an all aluminum engine will make a little iron.

Tim and all,

There's enough iron in the engine to make a drain plug magnet worthwhile IMHO. Cam gears, timing chain, cams, valve train, rods, crank, etc. Admittedly, some are non wearing. I pulled the cam position sensor once and it was covered with tiny iron particles.

Glen Murdock
97 Pacific Green

The issue may be less one of iron than design, it is very difficult to attract and hold sub 20 micron iron particles from a oil stream as it rushes by. Someone else told me that Super magnets don't lose their force at high temperatures, but the important point is that to be effective at all they have to work at an area where the oil will be still for a long time, like the bottom of a sump.

How tight should I tighten my filter to make sure it doesn't leak, but is still easy to remove?
The single biggest mistake people make when installing an oil filter is failing to use a dab of Dow Corning DC4 or any good silicon grease on the oil filter O-Ring before screwing on the filter base. Never use engine oil on the gasket as 50 hrs later when you try to remove the filter, the oil will have been long gone and the filter will not want to come off. We purposely have made our oil filter adapter easily removable with 4 bolts, so if you put the filter on like a gorilla, or you used engine oil as a lube, you can take the filter base off the aircraft and put it in a vise and deal with it there. Never try to remove a stuck filter on the firewall, as our mount is deceptively simple, yet very strong, and you have the potential of pealing back the firewall with brute force. We purposely did not provide a way of holding our filter base with a large wrench because if would provide you with a very large lever and increase to potential of damaging the firewall. Again, fix the problem, not the symptom. Use a dab of DC4 silicon grease and you'll never have a problem removing an oil filter.

One last Airwolf gem on oil temperature:

What is your definition of a "High" oil temperature?
On our website, we now have a new link that addresses this very subject, and specific things to look for. The first thing we do at Airwolf, is try to determine from the customer, what their definition "High Oil Temps" is. When we hear temps of 240-250°F, we get very, very concerned. I have been told that in Lycoming's service school, they tell the class that there is a temperature reading that you never, ever want to see on your gauge. Their comment is "AT 265°F, YOU HAVE TWO MINUTES TO LIVE" The temperature your read at your temperature gauge is actually 50°F lower that what the engine is seeing in the sump of the engine. Therefore at 315°F [265°F+50°F], you have no lubricity left in the oil. All you have is a liquid and engine seizure will occur.. Remember this the next time you climb out on a very hot day and your engine oil temps are at or very near the redline of your old non specific colored oil temp gauge. Now you see what it is really important to calibrate your temperature gauge.

I thought the +50° comment interesting, Gary Morrell reports 240° peak oil temporaries on the track so add 50° and we have almost 300° and a lot of reason to commit to synthetic oil for their heat resistance.

I think synthetic motor oil is essential for SHO motors that will see sustained high speed or sustained high RPM. The most recent tri-synthetic Mobil 1 is supposed to "protect your engine" (whatever that means) up to 400°F. Under extreme conditions the engine coolant alone can not keep up with the heat a healthy SHO engine can generate and the oil cooling system becomes far more important, and I just don't think conventional motor oil is up to the job for many enthusiastic drivers. Just as many SHO owners don't need Z rated tires every day they provide a margin of safety just encase a need presents itself, so too with synthetic motor oil.

Mercon ATF is stable up to 368°F but Mobil 1 ATF is stable up to 430° F which is a huge 60° safety margin. In spite of the ATX problems the Mobil 1 ATF showed only 2.2% oxidation and I credit it for saving my transmission.

Go to Part Three: Understanding the lubrication needs of the SHO (Oil Filters)

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