would like help diagnosing Low Oil pressure - Ford Powerstroke Diesel Forum
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Old 01-09-2014, 07:09 AM
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would like help diagnosing Low Oil pressure

First, thank you to anyone taking the time to help me. I've searched posts and tried some things, but now I need help about what to do next.

The problem: Low Oil Pressure, as measured at the stock oil pressure sender/sensor on the HPOP reservoir on the L front of the engine.

How bad it seems to be: I get a "no oil pressure" reading at idle, but my truck starts, runs, and seems to drive fine* (I don't know if I'd recognize reduced power since I've not owned a 7.3 before this one I just got).
-At about 900-1000 rpm on the factory tachometer, the dash oil pressure guage registers "on - good oil pressure"

What I think it means: My idle oil pressure is less than 5 psi, and at 900-1000 rpm it's >5 psi, assuming my sender is functioning properly.

What I've heard about it: Read this and other forums. Learned common causes for Low Oil pressure including: failed LPOP, cracked front cover face where it mates with the LPOP. Injector oil O-ring leaks. Failed/cracked/or blocked oil pickup tube, and of course Low Oil level in the pan!

What I've done about it:
1. Replaced the oil sender/sensor* (well, the previous owner did, said it didn't fix anything, so he left the wire disconnected)
2. Made a terminal and reattached the white wire/Red strip to the sender and got the dash reading I describe above.
3. Jumped right in and figured pulling the oil pump was next. It and the front cover appeared OK to me, but a Melling 208 may/may not be an improvement, so I installed one. The truck has 115,000 and has been driven, towing frequently, for 15K in this low-oil-reading state with no apparent problems.
4.Got a few stitches in my hand (at the kitchen table courtesy of my wife) when the 10mm flare wrench broke loose one of the oil pump bolts and and I nailed the sharp flanged edge of the oil pan.

What I'd like: Help!
I have a few questions, first of which is - is it possible that the reading taken at the stock location is inaccurate? Has anyone ever seen an oil galley blockage to that reservoir? The HPOP stays full and the truck seems to run fine, so I kinda doubt that..

What's the MOST likely cause of the low oil pressure? Replacing the LPOP didn't seem to fix it - oh well, at least that's narrowed down and I've got a new oil pump on there - my knuckle will be fine in a couple days - ha!

Seriously- what might folks suggest I try next?

I'm considering, in this order.
1. Put a mechanical guage in place of the sender to get quantitative PSI numbers.
2. Pull the oil pressure filter head, which I believe involves pulling the whole oil cooler assembly. In the head reside the excess pressure bypass valve, and the oil pressure regulator valve proper. Clean and inspect for stuck regulator or missing bypass valve parts, plugged oil cooler?
3.Do the "pickup tube test" - over fill crankcase (How much extra oil?) jack up the rear of the truck, and see if Oil pressure improves. I understand this immerses the pickuptube er, "to the hilt" and thus confirms a cracked or broken pickup tube, but wouldn't help to diagnose a plugged/blocked tube/screen.
4.Kinda get frustrated about the internal oil leaks that could be going on, and wonder how hard and expensive it might be to find and fix.
5.Seriously think about giving up.
6.Seriously think about driving it until it blows up and put in another used 7.3
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Old 01-09-2014, 03:37 PM
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I would start by putting a mechanical gauge on the HPOP reservoir to see what it is reading at NOT and idle. Then I might move it to the oil filter header port and check it there too. Cheers!
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Old 01-10-2014, 05:34 AM
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Patrick, I put a mechanical gauge on the HPOP reservoir and ALMOST got excited when, upon cold (40 degrees) startup, it registered 25 psi @ idle, and 40 or so with some rpms. Within a few moments, certainly before the engine was anywhere close to normal operating temperature, it dropped to 0 psi at idle, and hardly anything measurable ? 2-3 psi on the mechanical guage even with 1500-2k rpm.

I read on different forum where a person with similar symtoms did the oil pump, no help, and finally pulled the pan to find a piston oil squirter had come off and fallen down into the pan.

I fear a similar large internal leak. I've read that engines can run "ok" even with a pushrod or rocker damaged and have a large internal leak that was also. In that case, "taking a look under the valve covers" was suggested. I'm not sure what I'd be looking for.

Looking more and more like I'm going to be pulling this engine, ugh!
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Old 01-10-2014, 06:42 AM
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Patrick, your sig mentions a "relocated block heater plug" on your 97. When I looked at the oil filter head, I didn't see any port - except the very large one with what appears to be the block heater in it.

Why did you relocate the plug on your truck?

Are there other ports that I just can't see without removing the oil filter?
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Old 01-10-2014, 07:24 AM
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When is the last time the oil was changed? What oil was used? I think I would pull the valve covers, see if you see anything not consistent and pull the oil pan to see if you can see anything out of the ordinary.

sent from me
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Old 01-10-2014, 06:33 PM
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Quote:
Originally Posted by blueridgespeed View Post
Patrick, your sig mentions a "relocated block heater plug" on your 97. When I looked at the oil filter head, I didn't see any port - except the very large one with what appears to be the block heater in it.

Why did you relocate the plug on your truck?

Are there other ports that I just can't see without removing the oil filter?
It's the other end of the block heater cord (where you attach an extension cord to plug it in) that I relocated to the bumper. Anyway, there is another smaller port that is plugged on the filter adapter/header forward from the big block heater port. Chhers!
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Old 01-11-2014, 05:08 AM
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Thx Patrick!
-as for the answer to last post, 15w40 Rotella Dino oil 1400 miles ago. I would pull valve covers if I knew what I was looking for, but that's where I need help. And as for the pan, I hear piling that requires pulling the engine. I've pulled and rebuilt a few 4,6,8 cyl engines, but the 7.3 is quite heavy and the 18 hr r+r professional labor estimate has me intimidated
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Old 01-11-2014, 05:33 AM
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If you are running the engine with VC's off, you are looking for for relatively even oil discharge from the injector oil spouts and looking for oil leakage from around the base of the injectors (which would indicate a bad top o-ring). Cheers!
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  #9  
Old 01-11-2014, 06:40 AM
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Doesn't require pulling the engine, just unbolting it and lifting a couple inches

sent from me
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  #10  
Old 01-11-2014, 08:11 AM
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ATVrider and Patrick - thanks guys- this gives me more I can work on - I hope to be back with the results soon.
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