Well when we took the 79 out to SMORR a few weeks ago, I noticed a little rattling noise from the engine. It was running a little warm, the radiator was just caked full of muddy water, witch soon turned to mud.
I've washed out the radiator several times. Now after the engine warms up, my oil pressure drops. Factory gauges, don't really know how much pressure is there.
But the rattling noise is still there..... Truthfully if the motor's going to be toast, I'd almost park it, or try to get my money out of it. But I love that blue truck................

 

you cant sell the truck what engine i still have a few in the shop down home!

 

I wouldn't worry too much about it, Bob.

My oil pressure isn't the best, and it keeps on rolling. You can buy an inexpensive mechanical gauge for the oil pressure and run it into the cab to watch your oil pressure while you drive.

 

It's a400M

 

Frankly, the factory gauges leave a lot to be desired. If you'd like, you can pull the oil pressure sending unit and clean it out...or do what I did. I put in an extension tube, and reinstalled the factory sending unit about six inches above where it was originally installed...and used a tee fitting off the side of the extension to put an aftermarket gauge in the cab.

It ain't that difficult or expensive...

 

400m didn't have much oil pressure ether... had on that knock well it still runs today that's been 5 years...

 

The truck still runs strong. Just going by the factory gauges,my running temp looks good. But the oil pressure is shot. And I have a rattle noise that I'm sure is the engine. Don't like it.
Bob

 

I ran my 351m out of oil and she hammered. filled back up drove it for two more years before th ex hit it.

try lucas oil additev