This is the thermometer we put in Tracy's rear end - of the CAR I mean! (You guys are terrible!)  We wanted to incorporate some warning lights into the new gauges. This dipstick oil temperature sensor is sold by Gene Berg.  The little copper wire at the top twists around until, at 225 degrees, it contacts the screw with the red wire under it and your oil pressure light starts to flicker (or you can wire it to a separate light).  We filed
cross hatches in it for checking the oil but it was still hard to see so we keep the original dipstick in a hole in the firewall insulation for easy reach at oil-checking time.
    We got this nifty little thing installed just before I took Haifisch on a trip to Ohio & back (about 1,400 miles).  I was surprised when it came on with the oil temperature gauge reading only about 205-210 degrees.  We've run this engine hot a few times so we're very familiar with the symptoms.  When the oil temperature gets up around 130+, the oil pressure light will flicker at idle, the idle will be rough, the engine will leak oil noticeably, and upon opening the engine cover you are greeted with a blast of seriously hot air.  Well, I pulled over but the engine was fine.  No symptoms at all.  So I assumed the gauge was right, the Berg thing was wrong, and went on my merry way, running with the red light on solid, the temp gauge climbing as high as 240 at the top of a couple of mountain passes.  Haifisch ran great there and back and all was well...until I got home and checked the temperature of the oil with a very accurate photographic thermometer.  The Berg sensor was lighting the light at 226 degrees!  This meant that I overheated this car for hours on end, running oil temps as high as 260+!  Could it be true?!  Visions of Tracy throwing all my stuff out on the lawn, asking me through angry tears how I could be so thoughtless & cruel, ran through my head.  I started practicing my pleas for forgiveness ("Honey, I was thinking of how I had to leave at home for a week & through my watery eyes, I didn't see the warning light!" - "The guy at the gas station said not to worry about it!" (no-strike that one) - "I'm just a total idiot.  I wouldn't blame you if you never forgave me.  I should just go drown myself in the ocean for being so stupid.").  I was horrified but amazed that the car actually seemed unfazed!
 
    Well not exactly.  After trying two oil temp gauge senders and temporarily substituting a known good gauge, we have come to the conclusion that the Berg dipstick tube temperature sensor is giving misleading information.  The Berg sensor is taking the temperature at the top inch of oil, the oil that has just been superheated from lubricating the bearings, cam, heads, etc.  But the oil that flows into the pump and lubricates the engine is actually drawn from the bottom, not the top.   The
temperature for the gauge is taken from the side of this 2-1/2 quart oil sump that bolts to the bottom of the engine (the middle & left senders in this picture are for a future fuel injection upgrade).  The fact is that there is about a 20 degree difference between the top and bottom inch of oil in the sump. This also explains why sometimes the light comes on with the gauge at 200, and other times the gauge can be at 215 with the light off.  It just depends how the oil is mixing.  Maybe the dipstick thing works fine with the stock sump because there isn't much distance from the top of the oil to the bottom, but it obviously is not working correctly for our application.
    This is a great relief because it means that we don't have as severe overheating problems as we thought! In fact, as we have made it better & better, we have come to the point that we can cruise at 70-72 on the hottest summer days before the light comes on.  So if the light is actually coming on when the oil going into the engine is about 210 degrees, we are probably fine at the 75-80 mph cruising speeds that we have been trying to reach without overheating.
    Of course knowing all this, we could adjust the light to come on at 245 or so, assuming that the temperature of the oil going in to the engine would be around 225, but the right way to do it is to take the temperature of the oil as it's going in to lubricate the engine. The way to do that is to switch to Berg's screw-in sender and relocate both gauge and light senders to the oil fittings coming from the filters back to the engine.  Stay tuned...
 
    Our new VDO Cockpit Royale gauges did not come with built in warning lights. We wanted a professional, stock look to our warning lights so we purchased these LED's at Radio Shack and decided to potentially sacrifice one of our new gauges finding out if we could fit the lights inside. These 12 volt LED's come with built-in resisters so they are a plug-and-play deal.