Tim Denning
Junior Member
1986 D150 318 - I had a broken bolt hole where the fuel pump connects to the timing cover so I ordered a new cover, water pump, and timing chain. Since I was down that far, I decided to replace my rear main seal as well as the oil pump since I was having a low pressure issue (probably down to around 5psi) when the oil was hot. I installed a Melling high volume oil pump. I made sure to prime it before installation.
Initially my oil pressure read 60-70psi (using a mechanical gauge) at idle (while still cold) so I thought all was well. I drove about 200 miles round trip and by the time I got home, my oil pressure was zero. Water temp was fine at around 200 deg. and no ticking or knocking from the engine. I even got stuck in a 2 hour traffic jam in 90 deg. weather on the way home and the truck never complained.
The next day I pulled the distributor off and spun the oil pump with a drill. At first the drill had no load on it, then it would catch and oil pressure would start rising, then it would start free spinning and the oil pressure would drop, then it would catch again and show oil pressure. Oil pressure was finally constant so I re-installed the distributor and fired it up.
Again I have zero (or maybe 1 or 2 psi) oil pressure at idle. When I rev up the engine to around 2k rpm, oil pressure will climb to 70psi but will drop immediately to basically zero when it goes back to idle. I didn't notice any excessive ticking or knocking at all and the engine temp never got above 180 in my tests.
Of course the first suspect is the new oil pump but I've never seen that failure mode before. I was thinking that perhaps I didn't set the pickup at the correct height or that it dropped down and was touching the pan bottom. Or perhaps I didn't install something correctly when I installed the timing chain and I have a big oil leak that the pump can't compensate for at idle.
I will be dropping the pan and investigating soon but I thought I would check here first to see if anyone had experienced anything like this.
Initially my oil pressure read 60-70psi (using a mechanical gauge) at idle (while still cold) so I thought all was well. I drove about 200 miles round trip and by the time I got home, my oil pressure was zero. Water temp was fine at around 200 deg. and no ticking or knocking from the engine. I even got stuck in a 2 hour traffic jam in 90 deg. weather on the way home and the truck never complained.
The next day I pulled the distributor off and spun the oil pump with a drill. At first the drill had no load on it, then it would catch and oil pressure would start rising, then it would start free spinning and the oil pressure would drop, then it would catch again and show oil pressure. Oil pressure was finally constant so I re-installed the distributor and fired it up.
Again I have zero (or maybe 1 or 2 psi) oil pressure at idle. When I rev up the engine to around 2k rpm, oil pressure will climb to 70psi but will drop immediately to basically zero when it goes back to idle. I didn't notice any excessive ticking or knocking at all and the engine temp never got above 180 in my tests.
Of course the first suspect is the new oil pump but I've never seen that failure mode before. I was thinking that perhaps I didn't set the pickup at the correct height or that it dropped down and was touching the pan bottom. Or perhaps I didn't install something correctly when I installed the timing chain and I have a big oil leak that the pump can't compensate for at idle.
I will be dropping the pan and investigating soon but I thought I would check here first to see if anyone had experienced anything like this.