Pressurized Black Gold

Jan. 1, 2020
A vehicle's health is dependant on motor oil for more than just lubrication.

Frequent oil changes alone are no guarantee that an engine will last. Regular cooling system service, a tight air induction system, regular filter replacements and good quality fuel are all essentials.

Driving habits are just as important. A granny’s-one-owner creampuff might drive like a dream and look clean as a pin under the hood, but the engine’s innards might be full of sludge if she only drove it a mile or two at a time.

6.0L relief valve
The relief valve, found under and behind the balancer, tends to stick on 6.0L Power Stroke engines. If you remove the plug and the spring shoves the plug out of the hole into your hand, the relief valve is stuck in its bore and there will be little if any oil pressure. Metal particles can cause this problem.
Check for oil pressure by removing the filter, pressing the drain in the bottom of the housing to empty it of oil, then spin the engine with the filter cover off to see if the housing rapidly refills with oil. If there is no pressure, check the relief valve. If this valve is stuck, the crank-driven pump may well be destroyed along with the front cover.
(Photo: R. McCuistian)

Case in point: My brother-in-law bought a 1993 Acura Vigor that looked and drove like it was new. But the first time he drove it to Birmingham, sludge in the oil pan clogged the pump screen, and you don’t have to be a Master Technician to know how that deal turned out. He had to buy a replacement engine after owning the car only a couple of weeks.

A traveling salesman’s car can rack up some pretty large numbers on the speedometer if he or she keeps it in the wind. But with evenly spaced pit stops for regular maintenance as per the owner’s manual, it can last well beyond its expected lifespan.

Another example: My son now owns my old 1995 Ford Taurus with 250,000 miles on it. It hasn’t needed any major repair except a water pump. That’s because I maintained it so carefully when it was mine, and my son has continued that maintenance pattern.

Keeping things cool and clean Lost oil pressure can destroy an engine about as quickly as a rocket-propelled grenade, and more than a few engines have welded themselves together being starved for one reason or another.
Ford 7.3L Power Stroke Oil Flow Notice how the oil is drawn into the crankshaft-driven gerotor pump from the pan and sent under pressure through the oil cooler and filter head, which contains the pressure relief valve on this unit, before making its way to the crankshaft and lifter galleries. Also note the J-shaped piston cooling jets. The oil reservoir (top left) feeds the high-pressure oil pump, which sends 500 to 3,750 pounds of powertrain control module (PCM)-regulated pressure to the injectors. The oil filter bypass valve on this unit is built into the filter head, not the filter.
(Illustration source: R. McCuistian)

At the college where I teach, we worked on a 1999 Ford F-150 pickup that was running fine when the lady parked it, but the next morning the engine wouldn’t spin. We found the rod bearings had literally welded to the crank journals. After installing a crate motor from Ford, I explored the original mill but wasn’t able to determine what had caused the meltdown. The oil pump was in great shape, nothing was broken and the relief valve wasn’t stuck either.

But we all know there’s more toå the crankcase oil than lubrication. It also cools the parts and suspends solid contaminants so they can be removed by the oil filter. According to Ford, running a five-quart engine with just four quarts of oil can cause the oil to break down in as little as 1,500 miles.

A heart of steel The oil pump is the only mechanical component in an engine that receives unfiltered oil, and different engines drive these pumps in different ways. Distributor-driven oil pumps were once extremely common, with the camshaft driving the distributor and a hexagonal or slotted shaft from there to the pump. These early pumps were made of cast iron with steel gears and a pressure relief valve that was a part of the pump.
Toyota Camry Pump
This 1998 Toyota 2.2L oil pump (with its four-tooth rotor removed) is driven by the Camry’s timing belt by way of a dedicated cog. The oil pressure relief valve is on the other side of the timing cover mounted vertically. It can be replaced separately, but the timing cover must be removed.
We had this one apart because of a stubborn oil leak. Notice the broken rubber seal in the peripheral channel. After replacing a leaking camshaft seal (which is another pressurized leak point), we found that the oil pump seal was leaking as well.
(Photo: R. McCuistian)

Because oil pumps are positive displacement, they require the relief valve for overpressure protection. But that same valve also determines how much pressure the pump is able to shove into the galleries, which are drilled to feed whatever needs lubing and cooling from the crankshaft up.

Bearings shouldn’t have more than 0.0015 inch clearance or pressure tends to squirt past the loose bearings back into the pan instead of making its way through the gallery. That’s why using green Plastigage is so important when building an engine: No amount of micrometer measuring can be as accurate as checking actual bearing clearance with a flattened piece of green wax. Even a half-thousandth too much clearance can cause rumbling main bearings on an otherwise healthy powerplant.

Reinventing the heart The demand for lighter engine components brought aluminum-housed pumps (steel gears remain even today) that were still distributor-driven like the old cast iron units, but situated on the bottom of the timing cover. The pressure relief valve was likely to be somewhere else in the oil circuit.
Cutaway Oil Pump
This type of oil pump is one of the most common in use today. The tan-colored area represents oil suction from the pan and the yellow area represents splash oil. No pressurized oil gallery passages are visible in this photo.

The pump gears on those timing cover-mounted, distributor-driven pumps are accessible from the outside. If the distributor is mounted at an angle in the front of the engine, it will generally have an external oil pump on the opposite corner of the timing cover, pulling the lube through a tube and screen that leads back to the sump. Ever had to remove the oil pump plate on a late ’70s Buick V6 and pack the gears with grease to get it reprimed after an oil change? I have.

The Diligent DriverEd was an unusual guy I knew in the 1980s. He told me his 1974 GMC pickup died one day and that he had spent more than $400 to fix it. He had hired someone to fix it because, frankly, Ed wasn’t too “wrench smart.”“What was the problem?” I asked.“Timing chain broke,” he returned. That sounded interesting. How many small-block Chevy engines break a timing chain? Usually the chain on an older V8 stretches and causes the cam timing to run a few degrees behind, robbing the engine of vacuum and power. The next step is a stripping of the nylon teeth from the gear and an oil pan full of oil pump-locking nylon shards, but the timing chain generally stays intact. Ed continued: “When the timing chain broke, it bent most of the valves. This was the first unscheduled maintenance my truck ever needed.” My mind was still whirling around that broken timing chain issue. “How many miles did you put on it?”“I bought it with 2,500 miles showing, almost new. But the speedometer stopped working at 385,000.” As our conversation continued, I discovered Ed’s secret to a long-life vehicle. Remember I said that Ed wasn’t wrench smart? Well he decided that 1,500 miles was a long way to go on the same oil, so for the past 400,000+ miles, Ed had changed the oil and filter every 1,500 miles. Religiously. What engine wouldn’t last a long time with new oil in the crankcase every 1,500 miles? Ed didn’t know that was too often, and he was disappointed that his truck didn’t last longer than 400,000 miles – go figure. I spoke with the guy who does Power Stroke diesel work at the Ford dealer where I worked, and he was pulling maintenance on a 7.3L that had 600,000 miles on it. According to the owner, that truck had always enjoyed 15 new quarts and a fresh filter every 5,000 miles.

In the early 1980s, many engine designers began using crankshaft-driven gerotor or crescent gear oil pumps mounted in an aluminum housing behind the balancer. Many engines use this design today.
When the pressure is low for one reason or another, the lifters will generally begin to rattle. The Toyota Camry 2.2L oil pump is a peculiar little four-tooth gerotor driven by a dedicated cog via the timing belt. The relief valve is mounted several inches away from the actual pump in the aluminum front cover.

Dye Tells The Tale
The original diagnosis on this 1998 Dodge Stratus was a rear main engine oil seal leak – an expensive repair. But when we applied dye and a black light, we found the head gasket was leaking from the pressurized gallery that feeds the cam bearings in the head. The rear main seal had no leaks.
(Photo: R. McCuistian)

The 6.0L Ford Power Stroke uses an oil pump similar to this, and sometimes the relief valve mounted below the oil pump in the timing cover/oil pump housing will get fouled by trash that can destroy the pump.

Checking and tweaking A few years ago, I repaired a 2000 Jeep Cherokee. It was purchased with 33,000 miles on the odometer and ran like a dream until the first oil change.
4.0L Cam Bearing
This is the front cam bearing on a 2000 Cherokee that had an oil pressure problem even after the pump was replaced. With the pan and pump off and air pressure applied to the gallery, we found pressure escaping around these bearings. After we replaced the bearings, the oil pressure returned to normal. The rod and main bearings looked fine, and because the relief valve was built into the pump and there were no porous castings or cracks evident, it was a good bet that this was all the Cherokee 4.0L needed.
(Photo: R. McCuistian)

After the oil was removed and replaced, the pressure went away. Installing a new oil pump helped some, but the pressure was still alarmingly near zero with the engine hot. We removed the pan, pulled the pump and shot air pressure into the oil galleries. An awful lot of air hissed out around the cam bearings.

The first pump had failed, the resulting lack of oil pressure fried the bearings, but the camshaft was in good shape. The rods and mains were still pristine, so a fresh set of cam bearings put that one back on the road.

Years ago as a fleet mechanic, if I knew everything else on an engine was healthy and time was of the essence, I would add a washer to stiffen the oil pump relief valve spring. However, I would ensure that oil pressure wasn’t leaking past loose bearings and that the spring had weakened and wasn’t allowing the pump to do its best. In a word, the pressure relief valve is as much an oil pressure regulator as anything else. Not only does it relieve high pressure, it creates pressure by providing a calibrated restriction.

To prevent damage from a clogged oil filter, a bypass valve inside the filter or built into the filter head prevents oil starvation. But be careful: Some oil filters actually house the pressure relief valve for the lubrication system.

If you screw on the wrong oil filter, there won’t be any pressure at all in the system, and you just bought an engine. It’s easy for this failure to occur, especially if the filter threads, gasket, and other features appear to be a close match on a cursory exam.

I personally know of one oil change outlet that had to buy a Cherokee 4.0L because they used the wrong filter; the Jeep didn’t even make it a mile before the inevitable meltdown.

Other points to consider Overhead cam engines need pressurized oil feeding the camshaft through the cylinder head gasket. This is another possible leak point. Remember the Dodge Stratus we fixed that had a nasty oil leak from that head gasket passage?

So what are some other reasons an engine can lose oil pressure?
Foamy oil (too full or the wrong grade), slow idle speed, low oil level, restricted oil filter, oil that is diluted, a bad oil filter bypass valve or a hole in the pickup tube are just a few. Some other fairly obvious mechanical faults would be loose bolts at the oil filter adapter or oil pump, missing or damaged seals, a worn-out pump or a sludge-plugged oil screen.

Ever replace a set of lifters in a V6 only to have the engine lose oil pressure because of sludge migration into the sump? Missing or incorrectly installed gallery plugs; loose bearings (don’t forget the camshaft); and cracked, broken or restricted oil galleries are all possibilities.

I’ve heard that some mid-’90s Cadillac crank-driven oil pumps can lose prime in the time it takes to walk into a convenience store and back because of a stuck relief valve or a loose harmonic balancer bolt.

The fix? Check the bolt first. If it’s tight, the relief valve might be fouled. If that appears to be the case, dump 10 to 12 quarts of engine oil in the crankcase on top of the original seven to immerse the pump, then start the engine and rev it repeatedly to 3,500 RPM to reprime the pump. This will break loose the stuck relief valve.

Don’t drive it or exceed 3,500 RPM or you’ll whip the oil into a foam.
When you think you’re done, drain the oil, refill with seven quarts and recheck the pressure.

Along that line, my compatriot at the Ford dealership drew a ticket on a late-’90s Ranger with a nasty vibration that resulted from eight quarts of oil in a five-quart crankcase.

Keep it clean, keep it full, and run it warm to keep the odometer rolling. That’s my philosophy.

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