Worried about your oil pressure

[Robyn]

RecentlyI have had some hicups with DaHooooley under load and have been trying to diagnose it.
No codes and only does it every so often and then only after a real hard full throttle run.

To get to the point of this post, I decided to replace the oil pressure switch to make sure there was not an issue there and these are not bad to replace in the driveway or garage but a bitch alongside the road in the cold and dark.
Also I checked the fuel filter flow and I am replacing the PMD just because of the lack of codes and the intermitent nature of the issue.

Any way my truck has run about 40 PSI showing on the gauge when running at hwy speed and about 20 or there abouts at idle.
After a real hard pull with the trailer the running pressure would drop to about 35 and idle at slightly less than 20.

Now I have installed the new sender unit and the pressure runs at near 70 cold at speed and about 50 hot with the idle at 30-35 hot.
Now this in no way changed what is actually going on in the engine but surely proves that the electrical gauges and their senders do have a very broad spectrum of operating variables.

The one that came off was looking pretty sad on the outside with loads of corosion on the metal parts.
I cut it open to look at the contacts, the fuel pump contacts were a little thrashed but seemed to be functional.
There had been some oils seepage into the electronic parts of the unit but not terrible.

The operation of the pressure gauge is now smooth and more linear in its motion rather than jumpy like a froggy.

Not sure if this was even part of the issue but with an intermitent issue one can surely save a lot of grief by replacing a few of these little creatures as a preventive thing.

I have a new PMD coming in about an hour so with the OPS and the PMD we shall see.

Any time there is wierd operation of the gauge I would always suspect the sender unless the anomaly is accompanied by a bad sounding engine or other reasons to believe there may be internal issues.

Having a mechanical gauge somewhere in the dash area with your EGT and Boost gauges is a very good idea.


PEACE OF MIND :D

Hope this little tid bit help somewhere.

Robyn

[93GMCSierra]

on mine of course with the factory, or atleast I think the factory gauge and sending unit my idle pressure was always 40-45 and running was barely over that, maybe 40-47 I only seen it dip below that when it was low on oil.

[Robyn]

Normally the gauge will swing from about 20-30 at idle to about 45-50 running. The sending units get hinky on these things after they get some real time on the clock.

Robyn

[bl78ljb]

On the new GEP engine in my 'burb I get about 70+ psi when cold (not had it during real cold in the winter here yet) and fully warmed up at idle it goes as low as 45psi. Though I would imagine this is due to the reworked oiling system in the updated engine. In fact the readings were so different the mechanic who installed the engine for me even double checked the pressure readings. With the original engine I had oil pressure as low as 15-20 psi at idle.

[john8662]

Aw ha, see, I told ya these things can make some respectable oil pressure. You just have to have a good sender eh?

J

[bl78ljb]

A good sender and redesigned oil passages in the GEP block, the good thing is the new sender came with the new engine - what a deal!

[rustyk]

A common misconception is that a rotating crankshaft requires more oil pressure at higher RPM than at lower. The reverse is true. 30-40 psi is plenty at 2K+ RPM (engine loaded), and 15-20 psi is OK at idle (engine relaxing with a cool glass of lemonade).

Of course, the operator needs to ascertain (as has Missy Goodwrench) that the gauge speaks the truth.

In Robyn's case, the lower (35 psi) pressure is likely a function of oil temp, rather than another reason. But it's still plenty, but might suggest an external oil cooler; I routinely run my AMG 6.5L TD with 16K lbs., but that's what the motorhome in which it's installed weighs. I have an external oil cooler, and loaded, hit around 38 psi on the road. I also recommend Rotella T 15W/40 or Mobil Delvac MX 15W/40; anything else is, IMHO, junior varsity. When I was a lube engineer, my approach was: "Oil's cheaper than metal". Your call.

I'd wonder if the readings with the new sender unit are accurate, as the relief valve has something to say about pressures.

[93GMCSierra]

I always run Rotella 15-40 in mine, I agree that most brands are not as good. I do know that my Oil pressure was consistent, I only had lower pressure if the Oil pan was low, an I never had any higher.

[Robyn]

Temp for sure causes the oil viscosity to drop some and along with that goes the pressure.
The GM book calls for the pressure to be 40 psi at operting RPM.

Even 10 psi at idle will carry everything just fine but I certainly prefer to see 20+

The gauges on these things are not anything to write home to mother about.

When I rebuilt the 6.5 in the Burb late year I had a direct reading gauge hooked up on a T fitting for a while to check the accuracy of the dash gauge.
So So most of the time and accurate enough to be safe.

The direct gauge called the pressure at 55 Lbs down the road cold and about 45 hot with idle somewhere between 20 and 30 hot depending on the outside temp and how long it had been run.
The dash gauge graduations are a farse and give a good guess. The 40 mark in the middle is within a couple pounds on my 94 .

As I have stated in a few other posts, the dash gauges are more for looks.
Most folks dont watch them like us diesel freeks do so the factory simply does not put a lot of emphasis on the quality or accuracy IMHO

If it says ZERO its a good bet you have problems though.

A reading of 70 PSI on a 6.5 is very likely hinky as the pressure reg will dump before that.

My DaHooooley has the factory oil cooler but on the 3500 its an oil to air cooler only and does not go through the LH tank of the radiator like the Burbs do. ( At least my Burb is in the Radiator tank)

Your oil pressure should not drop off just because the oil is a little low. If its dropping its because it getting seriously hot or the pump is sucking air.:eek: and that is not good.

My 500 Cat will show slightly higher (5PSI) when the oil and filter is fresh.
After about 5K on the oil it will drop from about 60 PSI at road RPM (1400) to 55 and then stay there to the change time at 10K miles.
(Rotella T 15-40)
Been this way since new and has coming up 600K now.

Robyn

[93GMCSierra]

When I say Low I meant extremely, I had to add 5 + quarts, I lost oil because it was spraying out, I think the CDR was goofy and I was watching the spray out the oil dipstick and the cooler lines.