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Why would oil/filter change fix low/no oil pressure?

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Big6ft6

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My original repair thread is in the injection section. But now that it is fixed and I don't know why it is fixed, I thought I might get some more ideas here.

A month or so ago I fired up my 91 350 TBI k2500 and oil pressure didn't register on the dash gauge. It was a REALLY cold (single digit) morning when this first occured. After a few minutes it would just barely register on the gauge and if I increased rpm it would drop back to zero:confused:. Eventually after 6 minutes it would register about 10psi and not move at all with rpm. Before this my oil pressure gauge regularly would bury the needle and would fluctuate wildly at different rpm. So I assumed I had the common bad sender and it had just gotten worse now and was not registering, but secretly I was worried. I drove it this way maybe 5 or 6 times, nervously waiting for pressure to register on the dash gauge, before finally my concern got the better of me and I replaced the sender. I started the truck expecting full oil pressure...but instead found no change:eek1:

Now I was worried. So I pulled the pass. valve cover to watch for oil during a cold start. There was no oil at the pushrods until about 5 minutes after a cold start (See video in original post). The oil showed up at the rockers about the same time the dash gauge would begin to register some pressue. I thought maybe it was just the cold oil taking time to get up to the lifter and through the push rods so I picked up an oil pressure test kit and fitted the gauge in the plug hole just above the filter to test pressure there and started the truck again from cold...ZERO pressure :eek1: I immediately shut the truck down.

I was really bummed out, figured I had clogged or messed up oil pick up. I vaguely remembered this all starting not long after my last oil/filter change (I don't drive the truck often) so I figured, what the heck, I'll change oil and filter. I also stuck a piece of a wire clothes hanger with a little hook on the end up int he oil pan and blindly fished around after the oil was drained...nothing of note came out not even sure where I was sticking that thing. After the the oil/filter change I started the truck and low and behold instant gauge pressure at the dash and 45 psi on the test gauge:confused::dunno::woot:

Any ideas what could've happened? How could the filter have caused this? Wouldn't the filter bypass have allowed oil pressure to the engine even if the filter was completely blocked? What the heck?
 
Last edited:
Big6ft6 said:
My original repair thread is in the injection section. But now that it is fixed and I don't know why it is fixed, I thought I might get some more ideas here.

A month or so ago I fired up my 91 350 TBI k2500 and oil pressure didn't register on the dash gauge. It was a REALLY cold (single digit) morning when this first occured. After a few minutes it would just barely register on the gauge and if I increased rpm it would drop back to zero:confused:. Eventually after 6 minutes it would register about 10psi and not move at all with rpm. Before this my oil pressure gauge regularly would bury the needle and would fluctuate wildly at different rpm. So I assumed I had the common bad sender and it had just gotten worse now and was not registering, but secretly I was worried. I drove it this way maybe 5 or 6 times, nervously waiting for pressure to register on the dash gauge, before finally my concern got the better of me and I replaced the sender. No change:eek1:

Now I was worried. So I pulled the pass. valve cover to watch for oil during a cold start. There was no oil at the pushrods until about 5 minutes after a cold start (See video in original post). The oil showed up at the rockers about the same time the dash gauge would begin to register some pressue. I thought maybe it was just the cold oil taking time to get up to the lifter and through the push rods so I picked up an oil pressure test kit and fitted the gauge in the plug hole just above the filter to test pressure there and started the truck again from cold...ZERO pressure :eek1: I immediately shut the truck down.

I was really bummed out, figured I had clogged or messed up oil pick up. I vaguely remembered this all starting not long after my last oil/filter change (I don't drive the truck often) so I figured, what the heck, I'll change oil and filter. I also stuck a piece of a wire clothes hanger with a little hook on the end up int he oil pan and blindly fished around after the oil was drained...nothing of note came out not even sure where I was sticking that thing. After the the oil/filter change I started the truck and low and behold instant gauge pressure at the dash and 45 psi on the test gauge:confused::dunno::woot:

Any ideas what could've happened? How could the filter have caused this? Wouldn't the filter bypass have allowed oil pressure to the engine even if the filter was completely blocked? What the heck?
Click to expand...

Sounds like you may have had some trash blocking a oil passage ????
 
what brand filter was on it? what oil and how dirty?
 
Would just draining the oil have removed junk from the pick-up?

I can't remember what brand oil, but it was 5w-30. The filter was just a Fram filter. The oil would not have had many miles on it...maybe a few hundred.

Does the fact that the pressure would drop to zero when I increased rpm tell anything?

Can I tell anything by cutting open the filter, where would I look, I can't remember how oil flows through the filter.
 
so let's say the filter was totally trashed and could flow no oil through it. Wouldn't the filter bypass have opened and allowed oil pressure to the engine?
 
So it seems there are two theories.

1) Malfunctioning oil filter and a malfunctioning oil filter bypass.

2) Clogged oil pick up that was unclogged when I drained the oil even though I didn't see any debris while draining oil.

3) Other?

Which one seems more likely?
 
Yeah, so I've picked up on the "bad filter" theme. So does that mean everyone is leaning towards the filter was bad AND my bypass galley must be plugged/non-fucntioning as the most likely culprit?
 
run of the mill frams have less filter media as a good Wix (Napa gold) so it may be easier for them to clog up. I still think you may have had some trash blocking the pump pickup as well.
If you run into this again after a few hundred miles, you should drop the pan, check things out, and maybe drop a rod and a main cap to see what damage the bearings have incurred through this.

good luck!
 
129_1202_02+filter_fodder+group_of_open_oil_filters.jpg




Here is a good comparison article....actually the Fram XG tests pretty well, just the rest of them not so good.

http://www.gmtruckcentral.com/articles/oilfilter/1060.html
 
My 86 does that with a newer sender and rotella 10w-30 and a delco 1218 filter. Figured it was the cold causing the sender or gauge to act funny.
 
Thanks 76! That is good info and I agree to pay close attention, if it happens again I will park the truck and schedule a pan drop for warmer weather.

With 170K miles the engine has been a fighter. She looses a fair amount of oil between a few leaks and burning some in one cylinder, but she still has 150psi compression in each cylinder, I'd love to see her break 200k, but if she doesn't I can't blame her. I'll do what I can to help her out.

After reading Kansas twister, I Wonder if I accidentally grabbed the wrong weight oil and quickly dumped it in there without paying attention? If I had 10W oil in there instead of 5W in single digit temps could that cause this?
 
5W and 10W wouldn’t make that much difference. In your cold weather.. the 5w would be preferred… but with your high miles.. I would actually run 10w.

Change the oil filter to Napa, Wix, pur, etc.. - I know firsthand this could be the issue. Had a similar issue in my Silverado after changing the oil and filter ( used that cheap walmart filter) Someone told me to change the filter.. I did and it was fixed.
 
Thanks K5_Fla, your the first person to say they had a similar thing happen. Good to hear some confirmation. Maybe I will try some heavier weight oil, it might cut down on the oil I'm burning in cylinder #3 and some of the leaking. The funny thing (nice thing) is that it doesn't leak in the driveway...all the drips land on the exhaust cross pipe and burn off while driving, but you can see the wet oil coming down and the little baby drips hanging off the converter inspection cover waiting to become daddy drips once I start driving again.
 
just to clarify.. make sure if your gonna run Napa's, make sure it's the golds, not the regulars..

and no, 5 to 10 wont make a difference...
 
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