Ham's '48; Old Trucks Doing Silly Things

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?

There is a check ball that regulates oil pressure. When you start your engine at idle, the pressure is regulated at around 30 +/- 10 PSI. When you start out driving, the oil is still cold, so the relief is dumping oil back to sump until the oil reaches operating temperature, the pressure stabilizes.

Quote:

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Originally Posted by gmwillys

There is a check ball that regulates oil pressure. When you start your engine at idle, the pressure is regulated at around 30 +/- 10 PSI. When you start out driving, the oil is still cold, so the relief is dumping oil back to sump until the oil reaches operating temperature, the pressure stabilizes.

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Okay ... Another reason to let things warm up before I set out on an adventure.

Thanks.

My grand dad farmed with a 560 Farmall diesel. The engine was notorious for cracking heads. He would start it in the morning then do his daily maintenance until it was at operating temperature. At the end of the day, he would idle it for 20 minutes before shutting it down for the night. He never had any engine issues. I do the same for any of my non daily drivers, to include the air cooled units. I'm convinced it helps.