Chevy or GM pickup oil pressure - 5.7L and 6.0 L

[Marty Gulseth]

Hi all,

Trying to decide about keeping my older Chevy p/u or buying a newer used one. One thing I noted - on my oldie, '99 with 5.7 L, oil pressure at moving RPMs, warmed up, indicates just abouve 1/2 scale, 45-50 psi (no idea how accurate the gauges are...) and at idle, it drops to just above 1/4 scale. Seems to me it used to run a little higher at speed and did not drop nearly so much at idle.

So, I happend to test drive a newer Chevy with the 6.0L and noted very similar behavior. That kinda surprised me, and tenatively put me off on that particular truck. But, maybe my recall is incorrect, and this behavior is normal.

Anyone have one of these rigs - either engine - that can advise? Are those indicated pressures normal or are both engines showing signs of wear? Just collecting my thoughts.

Thanks much, regards,

Marty

[David Weaver]

Unless something has changed over the years (I haven't had a car with a pressure gauge in a while), that seems pretty normal to me.

In my youth, I spent a fair amount of time in old gas tractor seats. They'd drop to about 20 psi or thereabouts at idle when they were warm, and run somewhere around 50.

[Rick Potter]

Thinner oil in the new ones?

Rick P

[Jim Koepke]

Thinner oil in the new ones?

Rick P

I know in our Chevy Tahoe when the oil pressure drops a touch it is time to change the oil.

Your best bet may be to talk to a mechanic about this. It may be normal or it may indicate the oil pump is starting to show wear.

jtk

[Mike Olson]

I used to have a 99 burb with the 5.7 and when I decided to use high mileage synthetic my oil pressure sensor would do weird things. when it would idle it sat below 1/4 and when I gave it gas it would pop up just past 1/2 way.

I went back to regular oil and it still did it for the next year before I traded it in.

[Alan Bienlein]

Normal and nothing to worry about. I have a Chevy pickup, GMC Jimmy, Honda Accord and a Isuzu Rodeo that all do the exact same thing and verified it with a snap on oil pressure gauge.

You do not need high oil pressure at idle.

[Ole Anderson]

Normal and nothing to worry about. I have a Chevy pickup, GMC Jimmy, Honda Accord and a Isuzu Rodeo that all do the exact same thing and verified it with a snap on oil pressure gauge.

You do not need high oil pressure at idle.

I agree, I have an '07 Chevy 5.3 in my Jeep with a mechanical oil pressure gauge and that is how it reads, about 20 at idle, 50 at speed.

[Marty Gulseth]

Thank you all! For some reason, I just couldn't remember how the '99 behaved when it was much newer. I'm sure it has absolutely nothing to do with the fact that along with the pickup, I'm getting older...

Regards,

Marty

[Tom Stenzel]

Thinner oil in the new ones?

Rick P

No, for 2014 the 6.0 still calls for 5w-30.

The oil pressure gauge on my 1986 Ford Ranger would drop when the engine was revved. The warranty was ending soon so I put a known good gauge on it. Turns out the pressure sender was messing up, it got replaced. Then the oil pressure readings made more sense.

Incidentally my next vehicle was a 1989 F-150 with the 300 I-6. The pressure "gauge" acted oddly to me. It turned out that Ford had changed out the pressure sensor with a switch. If the switch was closed the pressure gauge read about mid scale. A guy I knew at Ford Engine Research admitted to me they had done that to reduce the number of warranty claims. I have no idea what Ford does now, that was a long time ago.

-Tom

[Marty Gulseth]

Well, in case anyone is interested - conundrum solved - I bought a Ford!

I wasn't hung up for or against any particular brand, and happened to spot one with most of the features I wanted AND very low mileage. That's the major reason for the switch.

Regards, Marty

[Jason Roehl]

No, for 2014 the 6.0 still calls for 5w-30.

The oil pressure gauge on my 1986 Ford Ranger would drop when the engine was revved. The warranty was ending soon so I put a known good gauge on it. Turns out the pressure sender was messing up, it got replaced. Then the oil pressure readings made more sense.

Incidentally my next vehicle was a 1989 F-150 with the 300 I-6. The pressure "gauge" acted oddly to me. It turned out that Ford had changed out the pressure sensor with a switch. If the switch was closed the pressure gauge read about mid scale. A guy I knew at Ford Engine Research admitted to me they had done that to reduce the number of warranty claims. I have no idea what Ford does now, that was a long time ago.

-Tom

Yep...a switch hooked to a gauge. I don't know what they do now, either--I haven't paid attention to my '03 E250 cargo van, but I suspect it's still the switch/gauge combo, too.

In the trucks from the late '80s and '90s, for those just tuning in, the oil pressure "sensor" was just a switch that would trip at about 7 PSI. As long as the oil pressure was above that, the gauge would show somewhere in the "normal" range. Below that 7 PSI or thereabouts, and the gauge needle would be in the red.

Otherwise, the oil pumps are mechanically driven somehow off the engine (in the '87-'96 Ford trucks, it was off the bottom of the distributor shaft, which was gear driven off the camshaft, I think). This means that as the engine speeds up, so does the oil pump, producing more pressure in a non-linear relationship.

[Scott T Smith]

Normal and nothing to worry about. I have a Chevy pickup, GMC Jimmy, Honda Accord and a Isuzu Rodeo that all do the exact same thing and verified it with a snap on oil pressure gauge.

You do not need high oil pressure at idle.

Alan is correct. About ten years ago or so GM started lowering the oil pressure at idle because they figured out that by doing so they could improve fuel efficiency. Our 2005 and 2006 Duramax diesels both do the same thing; and this is what I was told when I inquired. Made sense...

[Curt Harms]

Yep...a switch hooked to a gauge. I don't know what they do now, either--I haven't paid attention to my '03 E250 cargo van, but I suspect it's still the switch/gauge combo, too.

In the trucks from the late '80s and '90s, for those just tuning in, the oil pressure "sensor" was just a switch that would trip at about 7 PSI. As long as the oil pressure was above that, the gauge would show somewhere in the "normal" range. Below that 7 PSI or thereabouts, and the gauge needle would be in the red.

Otherwise, the oil pumps are mechanically driven somehow off the engine (in the '87-'96 Ford trucks, it was off the bottom of the distributor shaft, which was gear driven off the camshaft, I think). This means that as the engine speeds up, so does the oil pump, producing more pressure in a non-linear relationship.

I suspect you could tell by watching the oil pressure on start. I've had Ford Rangers for years. The oldest one had a 'real' pressure gauge; the pressure indication moved into normal range over a second or two as the pressure built. The newer ones with the idiot-light-that-looks-like-a-pressure-switch just 'snap to attention'. I did see directions at one time to change out the switch to a pressure transducer. It was more than just a parts switch, it required additional bits to get the Ford gauge to read correctly.

[Fred Perreault]

Maybe I am all wet, but isn't the mechanical oil pump fed off of the engine in such way that greater engine revs produce higher oil pressure in some way?

[Marty Gulseth]

The short answer - yes. I think. I know that was the case a few years ago when I was still doing a lot of my own wrenching. However, there were, at the time, "high volume" oil pumps available for retrofit that produced much higher pressure at idle than the conventional ones. To my knowledge, most modern engines have a pressure bypass valve of sorts to prevent too high a pressure in the engine.

I presume that most, if not all, current vintage engines still use an internal mechanically-driven oil pump.

Regards,

Marty