96 K1500 Low Oil Pressure

[Ben Burrage]

I replaced my oil pressure switch, and went back to 5w30. Went to 10w40 initially with same low pressure symptoms. I now run Castrol Edge 5w30 high mileage oil and a Wix filter at 270k on 97 K1500 5.7L and all is good. Hope this helps

 

[alpinecrick]

I currently own four Vortec 5.7’s/5.0 with mileage from 166k to 267k.

In my experience there has been little or no difference in oil pressure at hot idle between 5-30 vs 10-30 vs 10-40.

There is a bigger difference between brands of oil than viscosity.

Of the various brands that I have tried, Valvoline High Mileage semi-synthetic 5-30 holds hot idle oil pressure the best. The Valvoline High Mileage 10-40 does as well, but on cold mornings at higher RPMs, even fully warmed up the oil pressure will read 50+ psi, and I don’t like to see that.

Supertech and Mobile 1 High Mileage 5-30 also have good hot idle oil pressure.

Also, don’t be fooled by those “high efficiency” synthetic oil filters—every one I have tried has significantly higher oil pressure than good quality oil filters like WIX/ NAPA Gold—which indicates a restricted flow.

The worst were the Purolator Pure One’s I tried that PEGGED my oil pressure gauge at cold idle........

 

[Schurkey]

Also, don’t be fooled by those “high efficiency” synthetic oil filters—every one I have tried has significantly higher oil pressure than good quality oil filters like WIX/ NAPA Gold—which indicates a restricted flow.

The worst were the Purolator Pure One’s I tried that PEGGED my oil pressure gauge at cold idle........

Is the oil pressure sending unit upstream or downstream of the filter?

If the sensor is upstream of the filter, a restrictive filter would LOWER the pressure. But not by a lot, because the oil filter bypass should open to allow flow.

Some folks plug the oil filter bypass. I don't.

 

[alpinecrick]

Is the oil pressure sending unit upstream or downstream of the filter?

If the sensor is upstream of the filter, a restrictive filter would LOWER the pressure. But not by a lot, because the oil filter bypass should open to allow flow.

Some folks plug the oil filter bypass. I don't.

On Chevy gen 1 small blocks oil flows from pump, through rearmost main bearing, through filter, then up to rear of main gallery right next to the pressure sender, and through rest of the system.

if flow is restricted through filter (from plugged media—regardless if it’s dirty media or media that restricts flow), the filter bypasses. In bypass state the main gallery receives a stronger flow because the oil is no longer having to flow through media (and all properly functioning filters slow the flow down somewhat), and will show higher than normal pressure. That’s why on cold start we see a higher pressure reading than hot engine oil pressure.

Now, I know that you know all of the above and are just testing me.....

With the Purolator Pure One it pegged the oil pressure gauge on start up (I’ve never seen that even in 20 below weather with the truck left outside) This suggests that almost ALL the oil flow was being bypassed up to the main gallery where the oil pressure sender is located.

 

[Schurkey]

The filter bypass is controlled by a spring. There has to be ~5 psi difference between "filtered" oil and non-filtered oil pressure to open the bypass valve. Of course the filtered oil pressure is lower than unfiltered pressure.

The bypass is something of a restriction due to the size of the passage.

Plugged filters--or collapsed filter media--generally lowers oil pressure.

My trucks peg the gauge winter or summer when first started. Cold oil naturally raises pressure due to it's thickness, not because it's bypassing the filter.

 

[countryboy17]

hey guys i have a 1992 6.5 diesel runs greats starts every time with ease and i have normal oil pressure when i first start the truck after driving for a hour oil pressure will drop to 20psi when im on the throttle its 40psi and up when it idles it goes down to 20psi?
possibly a cdr valve?

 

[Schurkey]

hey guys i have a 1992 6.5 diesel runs greats starts every time with ease and i have normal oil pressure when i first start the truck after driving for a hour oil pressure will drop to 20psi when im on the throttle its 40psi and up when it idles it goes down to 20psi?
possibly a cdr valve?

Sounds normal to me, but I don't work with 6.5L diesels.

 

[PlayingWithTBI]

if flow is restricted through filter (from plugged media—regardless if it’s dirty media or media that restricts flow), the filter bypasses.

If the filter indeed has a bypass, some don't come with one.

 

[Schurkey]

Most filter adapters have a bypass built-in.

For example, the brown disc of https://www.summitracing.com/parts/ses-3-60-08-900/make/chevrolet

You must be registered for see images attach

 

[SCPilot1161]

So finally got the chance to put a mechanical gauge on the truck today. Lowest reading I got at idle was 9 PSI at 600 RPM. Low for my liking but still within spec so I don’t really see any point in changing the engine out? Other readings:
1000 RPM: 18 PSI
1500 RPM: 25 PSI
2000 RPM: 30-33 PSI