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Low/No Oil Pressure **(not) FIXED!**

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Big6ft6

1/2 ton status
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Apr 26, 2010
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Location
Madison, WI
***just updating for future forum surfers to recant my previous claim that I fixed this issue - Changing oil filter only fixes the problem temporarily, it eventually comes back regardless of filter type and especially in cold weather, no fix or cause known at this time***

****original post below*****

91 TBI 350 with 170k miles. Recently (since cold weather?) the oil pressure gauge has taken a long time to register any oil pressure after I start the engine. Like 3-5 minutes:eek1:!! After this it seems to register ~30psi or so and not vary much with RPM. I've only driven it half-dozen times or so since this started.

Prior to this, it would always read really high...sometimes pegging the oil pressure gauge and it would vary quite a bit with rpm.

I repalced the sender (under the distributor) today and it still reads zero at start up which leaves only two possibilities..a bad gauge or I actually have no oil pressure. Is there any easy way to confirm oil flow at start up? Is there an easy place to stick an analog oil pressure gauge?

Any ideas?
 
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With the motor running look inside your valve covers. Do you see oil squirting around your rockers? That can at least tell you that oil is pumping.
 
Pull your oil pressure sender. Crank it or have someone crank it for you and hold your finger over the hole. If it looks like you struck black gold, you're good to go :D :screwy:
 
The sender is under the distributor so I would have to remove the distibutor again, then remove sender, then re-install distributor, then start engine and put finger on sender (while laying in the engine compartment) then remove distributor to reinstall sender then reinstall distributor....I was hoping to avoid this approach, but it is obviously a valid one.

I was looking through the oil filler hole in the valve cover when it was running, after cold start not much sign of any oil flow, but if I drive somwhere then look there is a stream of oil running down the outside edge of the head, but oil isn't "flying around" what should it lookl ike if I look in the oil filler hole int he valve cover immediately after cold start?

Is it possible to have no pressure/flow at start, then have flow later?
 
you should have oil up to the rockers within a few seconds of start up...and if you took the v/c off, when at operating temp, rev it, and it should be strong enough to spray you in the eye if you are close to the rockers!:thumb:
 
Thanks 76...would I see it flying around through the oil filler hole or do I need to remove the valve covers? When I say it has been "cold" I'm talking single digits and the truck is parked in the driveway. Do you still think I should see oil actually flowing under the valve covers within a few seconds?

What about the fact that I've driven the truck this way a few times where the oil pressure barely registered for the first few minutes of running the engine. How long would I get away with this if there was really no pressure?

Another wierd symptom is that once the oil pressure finally registers on the gauge, when I first start driving the oil pressure drops to zero when I accelerate. After the engine fully warms trhis doesn't happen anymore.
 
sounds like a partially plugged pickup, or just worn pump....what oil viscosity you run?
Conventional oil when cold, you might as well think of it like molasses...it will move but slowly and thick. No oil pressure isn't good as you know, but once the engine is hot for 15 min or so the oil should be up to temp as well...I'm not sure how much you can see through your v/c hole, but it should be running closer to a water viscosity by that time. When it thins out like that, you should have plenty of oil....a stream of it flowing from the bottom of the head back down into the block, which it sounds like you do. There is a lot of pressure on the cam (I believe this to still be a flat tappet engine) and the lifters and cam can wipe out without sufficient lubrication, as well as galled rockers and pivots. Is your engine a big pain to get the v/c off?
I had a 95 TBI that had low oil pressure at 150K and wiped a rod bearing shortly after, so you really should figure this out. You may still be able to recover the engine if indeed it is a oil pressure problem, not just a sender.

good luck and post up some more, plenty of brothers that live for this sh!t..!
 
Thanks 76...I try to "close out" all my posts witha solution, it is one of the few ways I feel like I can give back. (and I can't stand when i find a post where someone had the same problem but they don't ever post the solutions!)

The valve cover is a pain becuase the alternator bracket is in the way on one end and another bracket on the other...no way I can find to wiggle out, but I can lift it about an inch and see the rods and rockers. Could also check the other side.

Yes it is a flat tappet engine and I run 5w-30 per the manual. If I were able to remove the valve cover do you think I should be able to see something within seconds of start up?

I'm half tempted to just do what xenomarine says and just see if oil sprays out the sender hole, but I'd rather not remove and install the dizzy twice in the winter in my driveway if I don't have to.
 
Can you loosen the sending unit without taking the dist out?
If you do pull the dizzy to check oil, put a good gauge and a makeshift line on the block to see what you got. If the lifters don't bleed down, (do they tick tick tick when you start it cold?) within 5-10 seconds you should have oil at the rocker arms, although maybe only a drizzle at that point, if its single digit temps.
Mine would start up, and within 2 seconds have 30# on the factory gauge, when it was warm, it would drop down to 15 at idle, idealy a little low.
Realize that not only does the oil provide lubrication to the moving parts, but it helps cool them when hot as well, so if you don't have good oil flow to the springs, they could lose their pressure some as well.
 
Ok, so I took off the pass side valve cover and started the truck from cold. Had been idle for days prior to this. Here is video of cold start and no oil flow (long and boring) http://youtu.be/q1OsgWd2HW4

It ran for 5 minutes before oil showed up on one of the middle rockers. The oil started out from just one of the pushrods, but the others followed suit fairly quickly. Here is a link to a video taken 6 minutes after i started the truck, it shows the oil flowing at this point. http://youtu.be/QEuX-Vj-NCQ

Any thoughts about it taking 5 minutes to get oil to the rockers? Even after everything is warmed up and driven (I took a 10 mile trip afer I shot these videos with no problem) factory dash oil pressure gauge never reads more than 10psi...and it doesn't move with rpm.
 
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how long has this been going on?
did you do anything prior to noticing the drop, like oil change, oil flush, different oil filter, hit the oil pan on something...etc.
Is the oil level full?
I'm thinking it may be a pickup that is restricted (by debris in the pan, or not enough clearance between the pickup and the pan), a pickup that fell off the pump, excessively worn pump, blocked oil passages, or filter.

If none of those things checks out, I would pull the dizzy and do a gauge test....if that confirms what the gauge reads, I would pull the pan and find out what's going on in there.
I would NOT drive it or run it anymore though.

You should have at least 20lbs at warm idle, 30 or so if cold, and add 10psi to every 1000rpm over 2000 for oil pressure.
 
OK, I see the oil, that is good but weak flow I think...check those items in the last post and see where that leads ya!
Goodluck
 
thanks 76, yeah, I think I will order a gauge and gett 'er done. That is the only way for peace of mind. Pulling the dizzy won't be such a big deal if I remember to mark the rotor position this time!:doah:

I don't know for sure but I think I did do an oil/filter change not long before this started and also switched oil brands...but I've done this before without problem. I few thousand miles ago I did run some addiditive though the oil (engine Rx) because I was afrad I had a stuck oil ring in one cylinder becuase Iw as burning oil and had a fouled plug. So it is possible that some debri worked loose and has now clogged the pick-up. However I don't really want to think about that:whistle: also every time in my automotive tinkering that I think my problem is something terrible/complicated/lethal...it ends up being something simpmle (like a gauge)....but there is a first time for everything:dunno:
 
you don't have to pull the dizzy... it's down low next to the dizzy on the back edge of the block, 1/8 NPT hole... ya might have to take off the cap to access it better but thats about it...

I've changed out a 1000 chevy oil senders and NEVER pulled a dizzy..
 
ryoken...you have super-hero like skills when it comes to this stuff I'm just a normal guy (I remember your build threads!).

The sender that was in there requied a 1"+ open ended wrench..and I could not slide a wrench that big under the dizzy base and achieve enough room to turn anything. My experience (with only a handful) is that the sender is often stuck in there pretty good. (of course my new one I just put in shouldn't be) So you need a good purchase with a good wrench to torque it unstuck, but that same torque also caused me one time to break the brass 90 degree fitting that the sender threads into, and it broke flush with the block.:eek1: So I'm a little gun shy now.:D

Anyone have a good diagram or description of how the oil flows through a 350?
 
right tools for the right job... :D


that sending port is the first downstream of the filter..


and my apologies for not actually reading thru the thread and just kinda jumping in at the end..

oil pumps rarely go, that being said, I just took delivery of Mutt who had a bad one... 91.7% of the time, it's the sender...

and always remember something I try to get people to do is, process of elimation.. cut off the avenues of failure.. a temp mech gauge is probably THE first thing I do when I come across a pressure issue.. it's an often used tool in my biz, as are a compression tester, etc..
 
What about the port just 1" above the filter on the side of the block? If I remember correctly earlier c/k had a separate gauge sender at this location and the location under the distributor was a "switch" only? Can anyone comfirm this? I just unscrewed that brass plug there...I guess a quick crank of the engine would tell me quick if I that goes to an oil galley!:D Maybe after lunch I'll do that.
 
yup, that's an oil port too.. run many a gauge off there...
 
Well...bad news. I picked up a oil pressure test gauge from the local chinese import store, threaded it into the port above the filter and fired her up.....nada. Nothing. This freaked/s me out.

So, although I can't think of why this would matter, I'm doing and oil/filter change now...just waiting for the oil to drain out. This did seem to come up after my last filter change, but that doesn't explain zero pressure. Even if the filter was totally blocked, I would be getting pressure via the bypass so don't have much hope that this will do anything.

I'm starting to fear the worst...clogged oil pick up. I have run some cleaner though the oil in recent months and have been running Penzoil with the "active clean" stuff...so probably some giant hunk of varnish came loose (or more likely many little ones) and they are all jammed up in the oil pump pick up.

I've never pulled a pan on a engine in a vehicle...doesn't look aweful...but not even "simple" repairs are simple in the winter in your driveway with numb fingers and snow falling in your toolbox.

I'll report back shortly
 
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