Oil Pressure range

[aggies09]

Hi all. Jen and I are headed up to Michigan and I have noticed that my oil pressure gauge appears to be registering somewhat lower than I remembered. Most of the way from Texas to St. Louis it registered 38 to 40 psi at normal speed and would drop to around 20 psi at idle. I have witnessed no warning lights or other signs that would indicate a problem. All fluid levels are good.

What are thoughts on this issue and what are some things to check while on the road?

My rig:
97' XLV
88000 miles
OTR air

[Steve Bennett]

Tony, take a look at the mechanical oil pressure gauge in your engine bay, and compare it to the dash unit. We have seen a significant variation, usually on the low side between the mechanical gauge and the electric dash gauge. There is a sending unit located next to your mechanical gauge, and sometime these can send a false reading if the orifice gets clogged by debris. Also remember that your actual viscosity will drop with an increase in temperature. One other thing to check is to make sure you are not getting fuel in the oil, as this will reduce the viscosity, and lubrication quality of the oil. If you notice an increase in the oil level, you may have an injector problem.

[aggies09]

Steve,

Thanks for the tip. I will check in the morning to see if there is a discrepancy in the readings.

[Jon Wehrenberg]

Tony,

You are within what is considered the normal range, however if what you see is an unusual reading for your coach, as Steve correctly points out it may be attributable to a number of causes. The issue about fuel in the oil was a valid concern on the 8V92 engines, but I don't think I have heard of it happening on the Series 60, but I would check the oil level and sniff it just to be certain that is not what is happening.

The pressure gauge in the rear is mechanical and virtually at the source. Have someone read the front gauge, while someone else is reading the rear gauge at about 1400 to 1500 RPM. When the engine is cold expect much higher readings. As soon as the engine is heat soaked and up to operating temperature repeat the readings at the same RPM.

You would have a heart attack if you saw how low the typical 8V92 oil pressure reads at idle. But low idle oil pressures on that engine are normal, so the key is defining normal for the conditions in your coach.

[aggies09]

Jon,

Thanks for the input. I read the two gauges several times during the day today to see where I was. The dash and engine gauge appear to be about the same all the time. I became concerned when I looked at the DD book and saw that I was supposed to be above 50 psi. This coach has historically ran around 42 psi. Oil levels and diesel in the oil appear to not be an issue. No increases in levels and no evidence of smell reflecting diesel contamination.

If you feel this is in the normal range, I will quit worrying about it and just monitor.

Thanks to you and Steve for your thoughts on this.

[Jon Wehrenberg]

Tony,

Once my engine is warmed up and running at highway speeds I don't think I see a sustained oil pressure of over 50 PSI. I'm going to OSH leaving Friday so I will try to remember to let you know what is normal for my coach.

JDUB and Mango will have their computers so they can continue to insult everybody. Maybe between the three of us we can remember to post the info.

[nrhareiner]

I have monitored the oil pressure driving over 45K miles in a bus with Silverleaf 400. This allows constant monitoring of many functions.

Normally when starting the pressure will be between 52-53 at high idle. It will go to between 48-51 when warmed up and under way. Once warm, the normal idle pressure (low not high) will decrease.

I have not seen pressures that stay above 52 while warmed up and driving.

I hope this helps.

[Jon Wehrenberg]

A service manual for late model EGR engines shows that the DDEC minimums for oil pressure are about 9 PSI at idle speeds, and 26 PSI at 1500 RPM. I don't know if these values hold true for DDEC III, but I would guess they are close.

[Jerry Winchester]

JDUB and Mango will have their computers so they can continue to insult everybody. Maybe between the three of us we can remember to post the info.

It's going to be a tough week and we aren't even there. Jon, just remember to pay homage to the big "Bite Me" sign just south of OSH on your way in.

[Jon Wehrenberg]

With Truk wisely finding an excuse to avoid the pain, I am approaching this with more than a little concern.