Oil pressure questions

[spark3542]

MY 97 burb has 136k on the clock. I've owned it for only 3k of those. I notice the oil pressure reads lower than I think it should, and also acts erratically.

First of all, oil level in engine is fine, and was changed within the last 2k or so.

With engine cold, pressure reads maybe 45 or 47 at 1700 rpms. Warm it will drop down to as low as about 17 at idle, maybe 25 at 1700 rpm. This seems disturbingly low. but please, someone give me a sanity check like "this is normal for a 6.5 diesel". If this is too low, is it typically bottom end bearings or a worn out oil pump?

The other disturbing thing is that while driving, with no changes in rpm, transmission, throttle, no a/c or defrost, or anything else, the needle will jump 10 psi, then drop 10 psi, then jump, then drop, etc., on an ongoing basis. I can feel absolutely nothing changing when this needle moves (meaning no sound change, no feedback at steering wheel or accelerator...just the needle jumping around). No other needles jump around, and there's no pattern to the jumping, like lights on, stereo loud, or anything else.

Anyone seen this before?

Thanks

Mark in MA
97 K2500 Sub 6.5TD

[Hubert]

1) What oil and viscosity are you using?
2) What is usual ambient temperature highs and lows?

If the truck is in good condition, hasn't been used hard, doesn't use oil etc. I would suspect bad sender, guage, ground, or connectivity issue. The dash guage is not really all that accurate anyway. Good for determining if oil is being pumped though and better than an idiot light. You'd be surprised at the gm specs. I think at idle 10 psi is all that is required (warm-hot). Warm at 1700 rpm you should see more maybe 30-40 psi I think. +/- a little is ok for the OEM guage I would think but should not bounce, fluctuate, or really move unless a rpm change.

Someone want to verify this if oil pressure drops to danger level won't SES or check guages light come on? I would think so??? Or is that right before its dead for oil or coolant sensors.

[john8662]

Normal Oil pressure:

95+ interior dash
-55-60psi cold idle
-30-45psi hot idle
-50-55psi hot at 2k RPM and better

The 92-94 model dash will report a little lower pressure, just the way the gauge is calibrated (from my observation, stone throwers welcome).

First and foremost, replace the oil pressure sensor/switch, and see if you see a change, if not, proceed to investigate elsewhere.

Two sides of the story to consider...

First off, this sounds like an oil pump that's got a bad oil bypass valve that's bypassing pressure prematurely, causing lower than exected oil pressure readings.

The reason I think this is the jumps you see in your oil pressure reading. I used to see this before my oil pump in my ol 95 started failing, it never fully failed, just had lower than normal readings one day for no reason. A new oil pump solved the issue completly.

Second, you've got a '97. 97 was the first year to use piston oil spray cooling using nozzles in the main webbing area that use oil pressure to spray on the bottom of the pistons. Since 97 was the first year for this, larger than necessary nozzles were used, leading to lower oil pressure when hot especially, not necessarily a condition of bad bearing clearances. I've compared the nozzles for the early 97-98 blocks and the 99+ later design. The later design incorporates a smaller nozzle hole. As a matter of fact, I had to replace a nozzle in my '97 block I assembled for a play project and it had the big nozzles, the replacement for the same size sprayer was smaller (ID, not OD), was updated.

I suspect you might have the first generation block and sprayers... So, it may be normal...

[spark3542]

I use 10-40 oil. Ambient temps lately in the northeast range from mid 60's for a low to mid 80's for a high.

Coolant temp stays pretty close to 190-192.

I believe I read elsewhere that 10psi per 1k rpm is enough. If this is the case, I'll leave well enough alone, and maybe eventually find a good mechanical gauge to add for reassurance.

Thanks

Mark

[DmaxMaverick]

You should be using 15-40 oil, not 10-40. Typo, perhaps?

If your gage is jumping around, suspect a bad connection somewhere. Check all grounds and connectors. Clean them and reconnect with dielectric grease. While the gages are not known for their accuracy, they are generally reliable. The sender, on the other hand, is a more frequent problem.

A mechanical gage is an excellent idea. If the mechanical doesn't jump around, the problem is electrical.

[spark3542]

I used 10-40 for my first oil change. There was no 15-40 when I was shopping for oil, so I assumed 40 was the more significant number, it being the nature of the viscosity after warm.

Is my logic offbase?

Thanks

Mark in MA

[TAG]

I seem to remember back when the olds diesels first came out there were some issues with stuck rings due to the use of 10-40 oil. Seems i read somewhere the additive package used to achieve the viscosity spread was causing problems. If im not mistaken the owners manual says not to use any weight oil not listed. mine doesnt list 10-40.

[Hubert]

10-40 is not good enough. It probably is SJ oil. You need CH or CI oil. The S is for spark engines and the C is for compression combustion engines. I think the 2nd letter is the revision of the specifications - as new emissions and technologies evolve so does the oil requirements. The additive package is better suited for the soot and blowby contaminations of diesel fuel. Learned that on here reading stuff. Anyway even though they are both 40 top number 15w will still be a bit thicker and give better oil pressure too. Probably won't solve guage fluctuations but really better to use the correct oil. Mechanical guage is a good idea.

Oil is somewhat namebrand loyalty but Delo 400, Rotella T, Mobil are most popular recommendations and found almost anywhere Walmart, Kmart, or just about any truck stop. Try and buy the latest one made don't buy the stuff that has sat around a long time and shake it before putting in the truck. ( I shake just about everything but beer).

[Robyn]

OK
To give you a baseline reference.
The GM manual I have here in front of me says "Hot running" 40 psi
"Hot Idle" 20 psi
My 94 which I just rebuilt will run about 50 cold running and 40 idle and 40 hot running and 20 hot idle.
If its really hot out 90 plus it might drop down to slightly under 40 running and slightly under 20 at idle.
The factory gauge sending units suck too as do the gauges.
replace the sending unit and see if this makes it more stable.
Its in the rear of the engine valley under the intake maifold.
You can get to it but take a few colorful expletives along to help

OH BTW I am running Delo 400 15-40 in my 94

[spark3542]

Thanks for the info. I never realized the S in SJ stood for spark. I'll be a little more careful choosing my oil now.

[Bnave95]

Thanks for the info. I never realized the S in SJ stood for spark. I'll be a little more careful choosing my oil now.
http://www.burkeoil.com/pdf/oilguide.pdf
Live long and run strong;)