Looking Back

VEHICLE: 2000 Jeep Cherokee

MILEAGE: 39,257 miles

DRIVETRAIN: 4.0L engine, Auto Transmission

COMPLAINT: Low oil pressure

Flying blind can be costly and very annoying and it can take several different forms.  Some of the stupidest mistakes I’ve ever made were the result of my working on a vehicle I just wasn’t very familiar with.  The situation can become even more explosive when I erroneously believe I know what I’m doing.

Example:  Several years ago I replaced the timing belt on a Toyota Camry.  At the time, I had never worked on a Camry; the belt had only jumped a couple of teeth, but when I was installing the new part, I knew how to get the crank on TDC, but I had no idea where the cam gear timing mark might be.  I called the local Toyota dealer, and the technician I spoke with told me to line up the hole near the center of the cam gear with the round punch mark at the 10 o’clock position on the front cam bearing cap. He never mentioned the notch that bearing cap has at the 12 o’clock position, so I ignored it.  I used the 10 o’clock punch mark he told me about, and the Camry fired up and ran just fine.  As far as I know, it’s still running today.  Well, I thought I had gleaned some reliable insight from that experience.  Wrong!

Fast-forward to the here and now. This week one of my students had to replace a leaking camshaft oil seal on a Camry.  Rather than dishing out information or finding it for them I generally encourage my students to look the information up for themselves, but this time we couldn’t find the information in Alldata. The information had been there in some of the previous quarterly versions; another student found it when he was replacing valve stem seals in another Camry.  But the latest Alldata release (I pay about $1000 a year to keep my subscription updated) at that time, only showed a fuzzy 3 dimensional exploded view of the timing belt and gears along with several useless illustrations of how to inspect the belt itself, but no cam timing info was available relating to the timing belt. Those illustrations are better now.

But on that day, I faxed an information request to Alldata asking for the timing information that was absent from the DVD, but they never returned the fax.  Go figure.

Anyway, since we couldn’t find the information in Alldata, I explained the gear hole/punch mark deal to the student working on the Camry.  Well, it had worked for me, but it didn’t work for him.  The punch mark I remembered from my previous experience was present and lined up perfectly in the cam gear reference hole, but this Camry had no cranking vacuum and no compression with the belt installed that way.  The end of the story was that the student managed to find an old Motor shop manual in the department library that did have the cam timing information and he discovered that we should have used the 12 o’clock timing mark instead of the punch mark.  The Camry I had timed turned out to be the exception rather than the rule.  I told the students that I would have been better off in this set of circumstances if I hadn’t had any prior experience with Toyota Camry timing belts.  In that case, looking back caused me to hit a brick wall.

Searching for the Root of a Problem

Drawing on past experience caused the Camry situation to blow up in my face, but looking back is just about always necessary and a bit more complex than simply drawing on past experience to solve a problem or avoid a mistake. For example, when we find a failed part that doesn’t ordinarily fail, the temptation is to replace the part, clear the codes and run the vehicle down the road for a quick test drive, then move on to the next job.  Have you ever run that course and had the vehicle come back with exactly the same unusual failure a short time later?

Now it’s time to look back:  An ethical choice must be made, and it takes great integrity and candor to make that choice honestly.  We have to backtrack to determine why the part failed.  And who should pay for the second replacement part? This question can create an ethical quagmire, but it’s not usually all that hard to figure out, even if we don’t like the answer.  It’s a foregone that somebody will be unhappy.

Should the customer pay?  Maybe, but only if the failure is happening because of the customer’s neglect or abuse. If it can be determined that the customer hasn’t done anything to cause the problem we obviously should look elsewhere.

Should the manufacturer of the part pay?  Only if a manufacturing defect was at fault, and when in doubt, we frequently blame the quality of the part when a second failure occurs because it’s usually pretty easy to get the vendor to absorb the cost.

What if the counterman gave the technician the wrong part?  Should the parts department be responsible?  Not if technician gave the counterman bad information!

What if the part was installed wrong? Who should pay then?  Should the shop absorb the cost, or should the technician pay for his or her mistake?  This isn’t an exhaustive list of examples, but we all get the picture.  Frankly, nobody ever wants to pay, when this hand is dealt but the vehicle has to be fixed, and somebody has to absorb the cost.

Then there are those times when the cause of the original failure may be buried in a repair history that can stretch back across several owners and into the irretrievable past.

The Hot Potato Syndrome

       The Jeep was clean both inside and out with only 33,000 miles showing, and the soldier and his wife spotted it sitting at a used car lot.  The price was right, the paperwork was done, and the man and his wife drove away on their new ride. Since the engine oil was so fresh, they drove 6,000 miles before having it changed. Immediately after the oil change, the pressure tapered off to an alarming 7 pounds.  As the engine heated up, the pressure quickly dropped to zero. Time to look back: The oil filter was the right one for that engine, and there was nothing wrong with the oil that had been used. What now?  The sending unit was replaced to no avail. Still, the engine wasn’t rattling like the oil pressure was low.  A master gauge was installed to determine the true oil pressure, and it was evident that the pressure was indeed low.

The vehicle was taken to the local Jeep dealer, who verified that the oil pressure was low, and suggested a replacement oil pump.  Not a bad idea.  It was at this point that the tire store owner called me, laid the situation out, and asked my advice.

“Don’t just throw an oil pump at it.  Apply some air pressure to the oil gallery and see if you can determine where the oil pressure is going.”   I dropped by the tire store a few days later to find that the oil pump had been changed but the low pressure problem was still there.  The customer had taken the Jeep to a repair shop for a second opinion, and the repair shop checked the pressure and gave them only one choice:  They would need a $5000 engine.

The used car lot was approached for help, but all they did was to call the Jeep dealer and ask if Chrysler could help; after all, the Jeep only had 39,000 miles on it.  Chrysler’s refusal came from the valid point that the Cherokee had already changed hands four or five times (the car lot had purchased it at an auction in another state). If the vehicle had been sold to the present owner as a new unit, D/C would have been happy to pick up the tab.  The car lot apologetically but firmly refused to personally do anything about the problem.

Without passing judgment or throwing stones, here was a situation where nobody wanted to pay for the repair, regardless of who was actually responsible; the soldier couldn’t afford to fork out $5000 for a new engine, and so, after returning to the tire store for advice (and the tire store owner didn’t have any) the shiny red Cherokee was parked in the customer’s garage, unsellable, undrivable, and absorbing a nice portion of the soldier’s paycheck every month.  The tire store owner called me to ask if there was anything I could do.

Exploratory Surgery

“Pour a couple of bottles of Motor Honey in the crankcase so you’ll have some oil pressure and bring it over here,” I told him.  He and his wife showed up later that day to fill out the paperwork and I assigned two of my more experienced students to the task.

The first thing we did after verifying the low-pressure concern was to drain the crankcase and pull the oil pan, a fairly simple job on the Cherokee.   Removing the shiny new oil pump the tire store had installed, I applied a rubber-tipped air nozzle to the oil gallery and we heard a large amount of leakage blowing out around the cam bearings.

Incidentally, on the Cherokee 4.0L, the oil is picked up by the pump, shoved through the oil filter and up to the lifters, where a small amount makes its way through the hollow pushrods to the rocker arms.  The lion’s share of oil goes from there through four drilled passages that pass by the cam bearings on down to the main bearing journals, where it feeds through the drilled passages in the crankshaft to the rod bearings.

New Bearings, Good Pressure

The engine had to come out in order to do the job right; we recovered the refrigerant, removed the condenser, radiator, and grille, and got the powerplant out of the Cherokee, mounting it on an engine stand.  The cam bearings hadn’t spun but were badly worn, but the rod and main bearings looked just fine.  Gaskets and bearings were all that would be required; the cam bearing journals measured within specs, and the timing chain had only a small amount of slack.  Sliding the lifters back in their bores, we applied air and felt a good volume available at all four cam bearing ports.

The cam bearings on the 4.0L look almost exactly alike but are selective in size and design and must be installed in the proper journals. To their credit, my students discovered this peculiar design feature while checking clearances.

The new OE cam bearings are actually color coded and come with an instruction sheet, but the Sealed Power bearings we ordered weren’t color coded and came with the instruction sheet missing.  My parts supplier called Sealed Power and was told that the part numbers stamped on the bearings are sequential, with the highest number riding in the rear of the engine and the subsequently descending numbers fitted for the other three journals in countdown order. With the new bearings in place and air pressure applied, we found a much tighter gallery than before.  The leakage was gone.

With the engine reassembled and filled with new oil, a new filter, and new coolant, the gauge indicated a cold oil pressure reading of 60 psi.


We hadn’t found any concrete evidence of what had wiped out the bearings, so I called the tire store and spoke to Jeff, the tech who had replaced the oil pump.  Jeff’s report was interesting.  When he had first checked the oil pressure with his master gauge as stated earlier, he had seen 7 pounds at cold start and zero pressure with a warm engine.

Removing the oil pump and spinning the gears, they seemed to be loose, and when he shook the pump, it rattled.  He didn’t disassemble the pump or apply air pressure to the gallery. What was even worse was that the scrap metal man happened to be present and the old oil pump left in the scrap truck.  He replaced the rattling pump, filled the crankcase with oil and restarted the engine to find 50 psi at cold start.

Letting the engine run until it was at operating temperature, he still saw a comfortable reading on the gauge (he didn’t tell me the numbers) and thought he had cured the problem, but when the owner picked the vehicle up and drove it around town for awhile, the oil pressure continued to drop until it was near zero again.

Back to the Rear View Mirror

I had backtracked as far as I could and it appeared from the report I got from Jeff that the oil pump had been the causal component.  The reduced pressure would have allowed the cam bearings to wallow out, and while the new pump helped somewhat, the bearings were already past the point of no return.