No Oil Pressure at Idle

Tim Denning

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Dallas, TX
Ram Year
1986
Engine
318
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.
 

Fast69Mopar

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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.

I would drop the oil pan and inspect the oil pump pickup tube for cracks just to make sure. Then I would remove the oil pump and disassemble it for a close inspection. Make sure the clearance in the gerotor is okay and not excessive.

Also, if you installed a gasket between the oil pump and the main cap please remove it. A gasket is not required.

Another thing about the high volume pumps. It really is not necessary. The HV pumps take more horsepower to turn them and they can create more heat in the oil. Unless you are running this engine hard and in the upper RPM range you really don't need it.

Also, if you are set on running the HV pump please upgrade to the Milidon or MP oil pump driveshaft. I have seen too many stock oil pump driveshafts fail and shear off at the hex going in to the pump and then you will have zero oil pressure.
 
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Tim Denning

Tim Denning

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1986
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Thanks, it feels like I did put a gasket on the pump so I'll check that when I pull the pump off. One thing I forgot to mention was that I did the timing tensioner mod that replaced the cam plate with a timing tensioner/cam plate combo. I don't know if that had an effect. Here's a small video of that:

Timing Chain Tensioner Install
 
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Tim Denning

Tim Denning

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Update:

I may have found the reason why I had no oil pressure. It looks like the oil pump may have been damaged by some FOD although I don't know how it made it past the pickup screen. The pump and pickup were brand new. The damage on the outer pump and pump lobes match up. Whatever got stuck at that point caused damage to all 4 pump lobes in the exact spot. It's hard to see how such a small defect could cause 0 oil pressure but the pump tolerances are very tight. On the other hand, whatever caused that mark could have travelled on up into the engine and gotten stuck in the oil passage going to the oil gauges. I find that more likely since there doesn't seem to be any damage to the engine as far as I can tell. Also, I just noticed something in the last pic. Does that look like a crack in the pump shaft housing (circled in red)?
oil_pump.jpgpump_interior.jpgreceiver.jpglobe_damage_Moment_2.jpglobe_damage_Moment_1.jpgcrack_question_highlighted.jpg
 

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Tim Denning

Tim Denning

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Location
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1986
Engine
318
Follow up:

I've replaced the oil pump and rolled in new Main and Rod Bearings. I now have about 60 psi at startup and about 30 psi after warmup.

I don't have time for a full teardown right now so we'll see how it goes. I replaced the main and rod bearings out of an abundance of caution but I suspect the cam bearings aren't great either. All of the crank main and rod journals were still shiny and without scratches.

Here are some pictures of the worn bearings. The main bearings aren't too bad but the rod bearings are trashed. It's interesting that only the upper bearing halves had worn through to the copper layer. I guess that's a function of the forces being applied.

I don't believe the wear on the bearings was from the low oil pressure. I believe the original low oil pressure issue was due to the worn bearings.

We'll see how long my luck holds out.
 

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