Old trucks do silly things that puzzle us sometimes.

When I go out and wake up the truck to go for a ride, I’ve gotten in the habit of letting it sit and run for a couple of minutes to get the fluids circulating a bit before I hit the road; a good idea for old trucks and old guys too.

Off I go and the oil pressure sits nicely at 30 on the gauge - but, after about three or four miles (about five minutes at road speed), the oil pressure starts to gradually drop off until it almost gets down to the mark between 0 and 30 on the gauge (15 PSI?). Of course any drop in oil pressure gets my attention.

Then, after a couple of more miles, the oil pressure rebounds and once the truck gets into happy mode, it runs a needle width above 30 on the gauge for the rest of the day. I have checked and there is plenty of oil in the engine and nothing is making any unhappy sounds up in the forward engine room.

Just one of those things that make you go “Hmmm …?”

Any ideas?