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Topic: Oil pressure low at cold start - sensor issue? (Read 1187 times) previous topic - next topic

Oil pressure low at cold start - sensor issue?

The last two cold starts I've noticed that both the dash gauge and VMSpc show 30psi for oil pressure when the engine first starts, for about 30 seconds or maybe a little longer...then it jumps to 60psi.  In the past, I believe it went straight to the 60psi range when starting cold, as I would expect.

Does this sound like a sensor issue?  Is there an oil pressure bypass that could be malfunctioning in the ISM450?

Re: Oil pressure low at cold start - sensor issue?

Reply #1 –
Check oil level.

Re: Oil pressure low at cold start - sensor issue?

Reply #2 –
Oil level is right at the full mark.

Re: Oil pressure low at cold start - sensor issue?

Reply #3 –
I always preheat our engine if it's below 50 deg.

Re: Oil pressure low at cold start - sensor issue?

Reply #4 –
The pressure release valve should be shut when you shut the engine off, so starting
it would be closed and wouldn't open until it reached the set pressure so I don't think
it would be that. The best way to check it would be to pipe in a manual pressure gage
and check it with that.

Re: Oil pressure low at cold start - sensor issue?

Reply #5 –
Okay i guess ill step into the water, possibly oil slick. I never see 60 psi. Normal is 34 and idle around 17. I had put this in the happy place prior but now i guess ill re-address. So
What is the pressure seen by others? ISM 450
Scott

Re: Oil pressure low at cold start - sensor issue?

Reply #6 –
"Old" technology here. :))  Our 1989 Detroit Diesel turbo-charged V8 with 85,000 miles on it, with 15W-40 oil reads 75 PSI cold and 45-35 PSI when hot.
Not too bad I guess.
Well, I guess I had better amend my post.
First, let me say that we don't use the coach in the winter so temps outside are usually above 45 degrees.
Second, RPM on startup is around 1600.
Third, after heat up or driving about 20 miles, temp is about 190-215 degrees at 2,000 RPM and this is dependent on whether towing our Saturn Vue or inclines or steady acceleration around 65 MPH and even ambient temps outside.
We have used Shell Rotella 15W-40 and currently Mobil Delvac 1300 Super 15W-40 with the same results.
(how is that for details, Brett?)

Re: Oil pressure low at cold start - sensor issue?

Reply #7 –
Quote from: dsd –
Okay i guess ill step into the water, possibly oil slick. I never see 60 psi. Normal is 34 and idle around 17. I had put this in the happy place prior but now i guess ill re-address. So
What is the pressure seen by others?
Scott
36 running,20 at idle

Re: Oil pressure low at cold start - sensor issue?

Reply #8 –
Please, when posting oil pressure readings let us know:

Engine temperature-- cold start up at 32 degrees F will be completely different than an engine at operating temperature.

Engine RPM

Thanks.

Re: Oil pressure low at cold start - sensor issue?

Reply #9 –
When we left MN on Wednesday, it was about 4 degrees out.  I turned on the engine preheat a couple of hours before we left.  A very easy start. Engine coolant and oil temp were about 90°.  Transmission and retarder about 10° cooler.

My oil pressure runs 50  - 60 psi while the engine comes up to normal operating temp, the mid-30s with driving, 17 to 20 at a stoplight.

ISM11

Re: Oil pressure low at cold start - sensor issue?

Reply #10 –
Engine is ISM450.  With the engine cold, coolant and oil temps at 60* ambient, I normally see 60psi or so at cold start.  Idles at 725rpm.  Once warm, it will be 25-30psi at idle.

Re: Oil pressure low at cold start - sensor issue?

Reply #11 –
Quote from: WS6_Keith –
Engine is ISM450.  With the engine cold, coolant and oil temps at 60* ambient, I normally see 60psi or so at cold start.  Idles at 725rpm.  Once warm, it will be 25-30psi at idle.
Had me spooked for a second. Thanks for the replys

Re: Oil pressure low at cold start - sensor issue?

Reply #12 –
Anyone ever try a different brand of oil and get different results?

Reason I ask is that many (and I do mean many) years ago I built a 301 CU inch Chev engine and switched from Shell 10W-30 to Kendall GT1 Racing oil 10W-30 and saw a significant increase in oil pressure on the oil gauge (not an "idiot" light).

I realize there is a definite difference between gas and diesel engines, but just asking.

Re: Oil pressure low at cold start - sensor issue?

Reply #13 –
The reason for the question is that nothing has changed.  I haven't done an oil change (has about 5k on it) and this just started happening on my last trip.  Happened when we went to leave home and when we fired up to return home.

Re: Oil pressure low at cold start - sensor issue?

Reply #14 –
The best way to determine if this is a gauge/sender unit issue or actual oil pressure issue is to verify with a mechanical gauge.

Re: Oil pressure low at cold start - sensor issue?

Reply #15 –
Back in the eighties I worked for a airline and they had a SOAP lab. Spectrum oil analysis procedure lab. Would do samples on different oils to see how they were performing. 20% synthetic performed real close to 100%. Ill just stick with the recommended oil till they say otherwise and the Cummins preferred filter LN14001NN,  Lot of people have millions of satisfactory miles.
Scott

Re: Oil pressure low at cold start - sensor issue?

Reply #16 –
Quote from: wolfe10 –
The best way to determine if this is a gauge/sender unit issue or actual oil pressure issue is to verify with a mechanical gauge.
So removing the ISM oil pressure/temperature  sensor is rated very hi on the do not want to do scale of pain. I do have special wrenches, but the limited space i would not want to add in a direct reading gauge to test. Possible there is another plug that could be removed on the outside of the engine, I dont know
Scott

Re: Oil pressure low at cold start - sensor issue?

Reply #17 –
Quote from: dsd –
So removing the ISM oil pressure/temperature  sensor is rated very hi on the do not want to do scale of pain.

Scott,

That is a polite way to put it.

Mike

Re: Oil pressure low at cold start - sensor issue?

Reply #18 –
Quote from: wolfe10 –
The best way to determine if this is a gauge/sender unit issue or actual oil pressure issue is to verify with a mechanical gauge.
Interesting subject: pressure gauges.

My last "real" job was working for Schlumberger as a well testing tech.  Well testing is ALL about measuring pressure.  There is a great deal of industry effort expended in designing pressure measurement tools that are accurate, precise, and repeatable.  My then employer could afford to purchase (or design and build in-house) the highest quality test instruments available at any given time.  I spent many of my days (and nights), when not out in the field on jobs, in a lab where we verified the performance of our test tools.  We had extremely precise mechanical and electronic calibration devices that could measure the slightest deviation from "correct" pressure readings in a gauge.  If an "error" was detected, the gauge would be recalibrated, if possible.  If not, it was replaced.

The problem with calibrating a test gauge is that it is done using another test gauge.  So how do you calibrate the gauge which is used to calibrate another gauge?  The answer is, eventually, at some point you just say "That's good enough..." and live with it.

I remember these things whenever I listen to a discussion about pressure gauges.  In the beginning, most oil pressure gauges used on engines were mechanical.  Simple, responsive, and reasonably accurate.  Mostly, they either worked, or they didn't.  Then we entered the age of electronic pressure gauges, which added several layers of complexity to the process of measuring and displaying pressure.  An electric gauge requires a pressure sensor on the engine and a pressure readout (digital or analog) on the dash.  The sensor must convert the actual oil pressure into electric current, and send it to the dash readout, where the electric current is converted back into a pressure reading.  Lots more room for error, and in some cases manipulation, in that process.

I believe all of the Foretravel rear engine pusher coaches probably used electronic oil pressure gauges.  In the earlier models like my '93 U280 the pressure sensor on the engine connects directly to the dash gauge.  In later FOT models, there is a mysterious electronic blue/gray box between the sensor and the dash gauge.  I liked the way Roger (Roger & Susan...) described this box in one of his posts:

"All of the transducers for air pressure, oil pressure, volts, transmission temp, coolant temp and maybe speedo and tach feed into the box which does something to the signals and feeds a (likely) variable voltage to the gauge which causes it to show something."  Well put!  :thumbsup:

SO, bottom line, whenever we Forum members discuss our oil pressure gauge readings, we must remember that there are a LOT of variables involved in producing what the dash gauge shows.  I wouldn't be too overly concerned if the reading in one coach is different from another coach, even under what we assume is similar operating conditions.  Take the reading on your oil pressure gauge not so much as gospel truth, but rather as one of several general indicators of engine health.  The actual pressure number is not as important as how the reading compares to known past readings.  Whenever a radical change in the expected oil pressure number is detected, that needs to be investigated.

Re: Oil pressure low at cold start - sensor issue?

Reply #19 –
Quote from: Chuck & Jeannie –
SO, bottom line, whenever we Forum members discuss our oil pressure gauge readings, we must remember that there are a LOT of variables involved in producing what the dash gauge shows.  I wouldn't be too overly concerned if the reading in one coach is different from another coach, even under what we assume is similar conditions.  Take the reading on your oil pressure gauge not so much as gospel, but rather as a general indicator of engine health.  The actual pressure number is not as important as how the reading compares to known past readings.  When there is a radical change in the expected oil pressure number, that needs to be investigated.

This is both the dash reading and the reading on the VMSpc which is getting the info from the data bus.  The fact that it used to cold start and go to 60psi, and now goes to 30psi for about 30 seconds, then goes up to the expected 60psi, is what has me questioning what is going on.

Quote from: Chuck & Jeannie –
My last "real" job was working for Schlumberger as a well testing tech.
I had a friend that did this too...Kevin Taylor.  Super smart man.