Low oil pressure

[DrCharles]

When I added the factory turbo setup to my 7.3, I also converted the on-off oil pressure sender to a Duralast PS-4 (on the turbo), and jumpered out the resistor on the cluster. So I actually have a dash gauge that moves.

However, now that it's really hot, the oil pressure at idle (below 700 rpm) is so low that the sender opens completely and the gauge reads zero. That means the pressure is only 4 psi or even less:

• 0-4 PSI - Open Ckt
• 4-8 PSI - 24-36 Ohms
• 90 PSI - 8.5-17.5 Ohms

It comes right back up off-idle and through the operating range, fortunately. No lifter noises or other issues. Coolant temp is right in the middle of the temp gauge as it always is (new thermostat last year). Recent oil change using Delo 15W-40 diesel oil and a PS filter. (Mechanical lift pump delete so no diesel in the crankcase, although I will smell the dipstick and see again).

I guess the next step is to hook up a mechanical gauge and see what the actual psi is.
But what do I do after that, if it really IS low?

My old F150 with the 302 sludged up the pan pickup. Don't know if IDI's are known for this.
Dropping the pan on these is supposed to be really fun, and hard to get leak-proof afterwards.

 

[Thewespaul]

Around 7 psi at hot idle is completely normal. The oiling system in these is different from most gassers, it’s low pressure high volume, and with 8 open holes in the bottom end (oil squirters) it makes for not a lot of pressure, but a ton of volume.

 

[DrCharles]

That's reassuring, thanks. Should I go to 20W-50 for the hottest months, or just stick to 15W-40? Run any kind of flushing agent in case there's sludge at the pickup?

 

[Thewespaul]

Stick with 15-40w, I run it in all my IDIs even with 110+ days regularly. For flushing, the best thing I have found is to let all the oil drain then install the drain plug and fill the crankcase with clean diesel and let it sit overnight. Drain it the next day and youll be surprised how chunky it is from the sludge it has picked up. Ive done this on every oil change in the shop truck, and the oil will still look like honey for a week after putting fresh oil in. No other additive or snake oil has been able to do that for me.

 

[onetonjohn]

"For flushing, the best thing I have found is to let all the oil drain then install the drain plug and fill the crankcase with clean diesel and let it sit overnight."
What are you plugging? Dipstick? How much diesel are you adding? Filled to top? Are you pouring in the timing gear cover fill hole? Sounds like a great way to clean out sludge, albeit would be nice to have all the details before I try it at home.

 

[The_Josh_Bear]

+1 to real gauge double check

Slight out of the box thinking... you could also just raise the idle.

Mine is abnormally high ever since my LuK vlutch install but it doesn't bother me one little bit and helps with the stick shift starts a little. I raised it to get rid of the gear rollover noise.

 

[Thewespaul]

"For flushing, the best thing I have found is to let all the oil drain then install the drain plug and fill the crankcase with clean diesel and let it sit overnight."
What are you plugging? Dipstick? How much diesel are you adding? Filled to top? Are you pouring in the timing gear cover fill hole? Sounds like a great way to clean out sludge, albeit would be nice to have all the details before I try it at home.

I reinstall the drain plug in the oil pan, and fill the crankcase up to the fill line and just let it set. I fill it from the timing cover just like I’m filling it with oil.

 

[IDIBRONCO]

I also converted the on-off oil pressure sender to a Duralast PS-4 (on the turbo),

This is something else to consider. Your sender is as far away from the oil pump as it possibly can be. You'll always read the lowest oil pressure here. If you were to install the sender in another location, you'd probably see higher oil pressure even at a hot idle. A popular spot is in the oil galley that's on the lower, back of the block on the driver's side. It's right in front of the transmission bellhousing. In case you're thinking about using it, it has 1/8" NPT threads.

 

[DrCharles]

That's a good point... I fed the turbo bearing from the port on the top rear of the engine (where the original fake sender was located). I fabricated the oil feed from #4 Teflon braided line... I know the turbo is pretty worn, so I may be losing some (indicated) pressure there.

Someday I will send the turbo to Wes for a complete rebuild, when I can be without the truck for a while. That should be soon, before I start hauling firewood for the winter (should it ever get cold here again!)

 

[IDIBRONCO]

I'm not the most technical on the turbos, but I think that the oil pressure reading is taken before the oil enters the turbo on the factory style set up.

 

[DrCharles]

Yes, it's right there at the turbo center section inlet (in other words, at the far end of the feed line). So if the turbo is taking more oil flow due to loose bearings, there will be more pressure drop in the line and the sender will read lower.