To gauge or not to gauge?

My first VWs carried no gauges beyond what VW engineers thought appropriate.  Idiot lights monitored oil pressure, aged fuel gauges of questionable accuracy gave me a vague hope gas still remained in the tank, a red light told me if I was no longer able to stop, and another red light told me if the charging system was alive.  But no instrument observed oil or head temperatures.  Big Blue came equipped with my first set of aftermarket engine gauges, one for oil pressure and another for oil temperature. Not only did it seem like a good idea to have this important engine data available at a glance but more gauges on the dash looked cool!  However over time, the gauge needles began to migrate from the preferred value ranges and worry set in as I wondered if I would make it home before the engine died.  Then came the hours of troubleshooting, tearing the engine down, replacing parts etc….  I began to miss the days of driving in ignorant bliss as to what was going on behind me in the engine compartment.

Over the years I lost two engines mid-trip; one due to a broken crankshaft and the other broke a broken wrist pin.  I ran the former engine sans gauges and drove happily along for years until, when traveling Rt 95 in Baltimore MD on my way home form school, a rather loud bang followed by an eerie silence informed me that it was time to pull over and rethink my time of arrival (as well as mode of transport!).  When the crankshaft broke, it caused the distributor to shoot from its retaining clamp and bounce around the engine compartment (the loud bang) and without the distributor the engine will not run (the eerie silence).  Although Big Blue’s oil gauges carefully monitored the second engine during my cross-country trip, they did not relay the true nature of the doom which awaited me in the foothills of San Fransisco, CA.  While the oil pressure sensor happily marked normal pressure, the oil temperature sensor climbed, over the course of two weeks, from a standard of 190 deg F to 200-210 deg F.  During those two weeks, I stared in angst at that gauge pondering the possible reasons why my engine decided to run a bit hotter.  Since I was not anywhere near the resources for an engine pull and diagnostic session, the only choice was to continue on and try not to worry too much.  The latter proved to be just about impossible and when the wrist pin finally let go of #2 piston, I was a bit of a wreck (and stuck! But the rest of this story is for a future post).  In the following days, I began to wonder if these gauges were really worth the anxiety they produced on such a trip because, without gauges, the end result would have been the same yet I would have had two weeks of driving with more enjoyment and less angst.

Moby came outfitted with three gauges; oil pressure, oil temperature, and head temperature.  I cannot say my enthusiasm flowed forth freely when I saw them but when one falls for a bus one cannot always choose what accessories she brings along.  Since the PO installed them in the dash, I decided having them a better choice than three big vacant holes under the stereo.  The head temperature gauge was the first to make me reconsider after telling me the head temperatures over #3 cylinder hit 500 deg F during the first long road trip (350-375 deg F is normal).  The engine never showed any other signs of trouble and, in fact, continued to bring me back home without decreased performance.

Once home, the troubleshooting began as I replaced tin; pulled disconnected thermostat flaps; cleaned and inspected spark plugs; timed the engine; adjusted valves, carbs and dwell; and reset the head temp sensor. Nothing worked and research provided no insights beyond needing to break the engine open and go through it all with micrometers and such.  At some point in my frustration, I began to wonder if the gauge itself was the problem and perhaps my suspicions of an evil spirit inhabiting my engine a bit premature.  The gauge’s thermocoupler is set at 70 deg F and deviations in ambient temperatures above or below this threshold are known to cause false head temperature readings.  To test, I put the head temperature sensor in a coffee can of boiling water along with a meat thermometer; both the sensor and thermometer agreed that water boils at 212 deg F.  Bummer, the gauge seemed fine.  But wait a minute!  The engine does not run at 212 deg, it runs around 350 deg!  Could the gauge be faulty at higher temperatures?  After throwing away the water, I poured some cooking oil (canola I think) in the can and started to heat it up.  I quickly realized that my grilling thermometer does not read temperatures above 220 deg and switched it out for a candy thermometer (why I own one I have no idea, but it was nice to find a use for it) capable of reading up to 400 deg F.  When the oil reached 400 deg, I pulled the heat source, threw in the head temp sensor and watched both the thermometer and head temp gauge, writing down the readings for both as the oil cooled.  Sure enough the head temp sensor read high.  For the short term, I created the chart below using the data collected so I could track true head temps while driving.   Last April, I finally replaced the sensor and now get normal readings of 350-375 at cruising speed and 400 up long grades.  I found my bliss once more, albeit not so ignorant this time around!!

Although temperatures below 250 were accurate, these lower values in the chart are extrapolated from the candy thermometer data and therefore do not match. Presumably, the higher temp values have a greater difference than what is listed due to the calculation method.

That bliss turned out to be temporary because on the way down to the Natural Bus camp out a couple of weeks ago, the oil pressure suddenly dropped to 22 psi from its normal 32 psi at 180 deg F at 60 mph two hours into the journey.  Hello, stress,  I missed you.  After driving at lower speeds, checking the oil level, and staring a blue streak at the gauge, I decided the pressure ceased dropping and continued on to the camp out.

The following morning before departing for home, I once again checked the oil level, down a tad from the top fill line but still OK, and gave the engine a quick visual once over before starting it up.  Upon start up, the oil pressure resumed its normal value ~ 40 psi at cold start up then dropping to 15 psi at idle after warming up.  Twenty minutes into the trip, however, it fell back from 32 to 22 psi once more and stayed there for the three-hour trip back home.  I began troubleshooting the issue once home, starting with an oil change and a search for the dreaded metal filing/flakes that indicate internal self-destruction.  Luckily, no metal inhabited the oil, which seemed rather healthy overall.

With new oil added, the subsequent test drive began.  Oil pressure held at 32 psi after 10 minutes of driving, 15 minutes, 20 minutes….  As I drove and thought, I remembered the dual Kadron carbs make the engine tough to start after it sits and they require a little pumping of the gas pedal before cranking the engine.  Perhaps some gas made it down the manifolds, past an open valve, and into the engine case.  While not enough to raise the oil level, the gas may have caused oil viscosity to break down a bit.  25 minutes……  In addition, I thought it was odd that when the oil pressure dropped, idle pressure went to 0 psi on the gauge but the idiot light did not light. Designed to light up at 7 psi, the idiot light should come on if pressure reads 0 psi.  After 30 minutes of driving, the oil pressure remained at 32 but the oil temperature climbed from 180 deg F to an unusual 220 deg but I was back home at that point and parked the bus for the night, puzzled.

The next morning I decided the oil pressure dilemma could wait a few days until the cooler weather expected later in the week arrived.  My initial test drive took place on a much hotter afternoon than the drive to or from Natural Bus and while ambient temps should not greatly affect the oil temp sensor reading, the scientist in me wanted to complete the next test drive under conditions as similar to the original trip to rule out as many variables as possible.  The perfect morning came last Friday, and I took Moby out for a 40-minute run.  Both the oil pressure and temp read perfectly for the entire trip.

Now I am not one to run tests until I find the results desired as I would much rather find results I can trust should I decide to travel 12 hours away from home.  So Saturday, morning I took the bus out one more time under the same cool conditions of the previous day.  This time the oil pressure dropped to 22 psi within five minutes of driving!  The problem was becoming quirkier by the day and none of the symptoms pointed in any one direction for a cause.  About two minutes after the oil pressure fell, I looked over at the gauge and it read 39 psi!  Seriously??  At the ten-minute mark, the gauge began to slowly show a drop in pressure until, at 15 minutes, it reached 32 psi, and at 20 minutes hit 22 psi.  The needle remained at 22 psi for the remainder of the trip.  At this point, I felt the issue was definitely not with the engine as it ran very strong during the Natural Bus trip and all the tests drive and maintained perfect head temps and, for the most part, good oil temps.  There are very few reasons why oil pressure would fluctuate up and down because of an internal engine issue, and I saw no evidence of anything wrong inside the block.

At a stop light, I reached under the dash and moved the oil pressure gauge wires around, mostly out of curiosity.  An almost unnoticeable flicking of the gauge needle occurred when I pushed the wires up, so I left them in their new position and continued to drive when the light turned green (safety first!).  As I accelerated, the pressure rose and at 60 mph, read 40 psi.  Hmmm…. I reached under the dash and wiggled the wires some more…32 psi, wiggle…22 psi, wiggle…40, wiggle… 16, wiggle…32…PERFECT!  Not only have I found the issue, one that makes sense in light of the symptoms but I get to pick the oil pressure I reading I want!  Need a little stress in my life? Wiggle..20 psi.  Need to relax and feel good about the engine?  Wiggle…32 psi, ahhhh.  Need to feel extra special?  Go for 40 psi, why not?

While I still need to get under the dash and take a closer look at what, exactly, is loose/broken and see if it can be fixed or at least stuck in a position to provide suitable oil pressure readings, I ultimately think a replacement is in order.  Even if I know the cause, how do I know which reading is most accurate, the 22, the 32, or 40 psi?  I will admit that I have much less angst when I get to control what the gauge reads, it is kind of a novelty, and I wonder if I should not just pull it and return to driving in ignorant bliss.  On the other hand, I know from the months of April and May that when all the gauges seemingly work as intended, they provide a great reassurance that all is well.  In the end, I imagine I will replace the oil pressure gauge and maybe the oil temp gauge while I am at it but I do not think I will hold them in the same standard of reliability any more.  As long as the engine does what it is supposed to do, without any excess drama or stubbornness, I will watch the gauges for trends instead of absolute on the spot values.  Or I may just cover them up with electrical tape, who knows….


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