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OT Oil Bypass Valve

I

IndianaRed

Member
I've been having some oil pressure issues, 4.8 Chevy, and I think it may just be the oil bypass valve needing cleaned/replaced.

I've posted about this a few weeks ago. What makes me think it might be valave related is that I don't get any lifter noise at start, but after about 20 minutes of driving, about when that valve should be closing and sending oil through the filter. Just saw a picture of one and those holes are pretty darned small. I'm thinking mines gunked up.

I have a Chiltons manual for my truck, but it doesn't even list this valve in the index. Done some searching and can't find any info for my particular unit. I just want to get mine out to see if it's gunked.

I pulled my filter, but don't see any bolts holding the filter mount on. Looks like maybe the bolts that hold the oil lines to the side of the filter mount might hold that in place?

Any help is appreciated. And I've now passed 500k miles.
 
Valve is already closed. After the engine warms up and the oil thins out. Oil pressure drops.
Try some straight weight 50.
 
I think the valve located in gm filter system is to prevent drainback while sitting?? congrats on that kinda engine life-hope its not trying to give it up---
 
your problem is probably bearing clearance due to mileage ,but on the other hand the oil pumps are bad about wearing out on the newer model engines, we had a couple to start loosing oil pressure replaced the pump corrected the problem ,these had excess of 200k on them, a simple fix for us was to add 2 cans of stp or equivalent to the oil until we could repair them, oil pressure would stabilize were as before it would fluctuate bad when hot,most people have a problem with this method, but years ago i bought a super a tractor to farm with, man told me that the rings and rod bearings had been replaced right before he quit using it not the mains ,needless to say low oil pressure at low engine speeds when hot other than that ran fine ,didn't have the money or time to overhaul it so i poured in 2 cans of stp 4 qts of oil made that crop and several more, its still runs though but it's not used much now
 
While there is a oil filter bypass valve whether part of the filter or the engine. It would not affect engine oil pressure. The modern auto engines have full flow oil filtering and the bypass only opens if or when the filter gets so plugged as to cause a restriction.

The oil pressure regulator usually part of the oil pump, it is possible but doughtful. You are most likely dropping oil pressure when the oil heats up and thins out. If your hot oil pressure is too low then the condition of the bearings is the most likely culprit.
 
No dude, it's low when cold and normal when hot. And why would I get lifter noise 15 minutes after start up? Not at start, 15-20 minutes later. Isn't that when the valve should be opening, or closing, whichever sends it to the filter?

I burn no oil, no smoke, just got the highest mileage I've ever gotten with this truck, over 600 miles to a 31 gal tank. I don't think my bearings are that worn. But then I don't know nearly as much as you.

Changed the oil religiously, used Lucas, (not to start a Lucas debate), no other noises, no power loss. I think it's either the pump itself, or this valve. But wouldn't a weak pump be weak all the time?

Thanks B&D
 
No, not the anti drainback valve, the filter bypass valve. I know filters have them too, but there's one right inside the filter adaptor.
 
OK, one more time, (and I do appreciate the help).

Low pressure when cold. Comes up very slowly. When almost up to normal pressure, after about 15 minutes of idling, I start getting the lifter noise. That stays for about 5 minutes and then it's gone and I'm fine the rest of the day. Unless I shut it off for 30 minutes or more, then the same thing. Once warm and running, it's all just like new, normal pressure, no noise.

If the bypass valve is very clogged, that wouldn't affect pressure? Everyone else has told me the opposite. If oil can't flow well through the bypass, surely that affects pressure, can't see how it couldn't.

Scenario: Cold start, oil thick, bypass valve sticky and clogged. Where would the oil go? The valve is open, bypassing the filter, so the only route is through the valve and it's clogged. Has to affect pressure.
 
My manual says the valve bypasses the filter until oil reaches a certain temp. Everytime I start my truck it is bypassing the filter until oil is warmer/thinner and can flow through the medium in the filter.

At 10 below zero you'll never push oil through that filter. Even at 70 it's difficult. The bypass is not just for clogged filter.
 
Red, when the filter bypass valve is open, oil simply bypasses the filter and goes on to the bearings unfiltered.

It is NOT wasted, returned to sump, or sent elsewhere in the space-time continuum.

So oil gallery pressure is NOT affected.

First thing I would do is to connect an accurate mechanical gauge and see if the dash gauge is lying.

Besides the possibility of a bad gauge, that engine used a gerotor oilpump that is concentric with the crank snout and a LONG oil pickup tube back and down to the sump. SOMETHING could be going on allowing air to enter the suction side of the pump. (Noisy lifters can be caused by aerated oil, as well as by low oil pressure.)
 
The filter bypass valve still wouldn't lower the oil pressure. It just allows the oil to bypass the filter. The oil just goes directly to the engine.

If the pressure problem is caused by the pressure regulator then it gets dumped to the sump. I don't know how your engine is designed but it is usually part of the oil pump.
 
misunderstood your problem,no oil pressure at cold start up is either sump screen is stopped up or pump is worn out taking it a short time to fully prime up ,only relief valves i'm aware of is 1 bypass inside filter housing won't effect oil pressure as it only allows oil to bypass the filter not the engine, 2 is pressure regulator on the pump, only problem i've ever had with them was a broken spring the oil pressure was erratic because the spring was broken and somehow could screw together lowering pressure then then hang up in the housing increasing pressure.
 
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