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Old 10-30-2012, 08:09 AM   #1
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bcbowers's Avatar
Alpine Owners Club
Join Date: Mar 2009
Location: Surprise, AZ
Posts: 646
400 ISL - Minimum Oil Pressure

Since adding the SilverLeaf VMSpc system on my coach, I immediately began hearing a warning alarm and observed that the Oil Pressiure sensor was turning yellow while idling in gear at normal operating temperature (about 180 degrees). The sensor warning alarm can be adjusted to activate at whatever value is deemed desirable. So, the question is "What should the minimum oil pressure be for a 400 ISL?".

My coach was idling at 600 RPM. The dash guage shows the oil pressure at somewhere between 0 and 25 PSI but that guage is not graduated adequately to determine the exact reading. The VMSpc was displaying as low as 13 PSI which seemed rather low for such a big engine.

I recently had the engine serviced at Cummins and asked about the minimum oil pressure. I received the following information that seemed worthy of sharing:

1. The minimum oil pressure for the 400 ISL is 10 PSI. I did find this specification out on the Internet.
2. However, the minimum RPM should be closer to 800 RPM because anything lower is supposedly hard on the Allison transmission to maintain its minimum fluid pressure for proper lubrication & cooling.

I then asked the Cummins mechanic why they had set my idle at 600 RPM because they're the ones who last programmed the ECM. The answer was that they typically default the idle RPM to the lowest possible value (600) and expect the owner/driver to use the "Idle Speed" selector next to the left side of the driver's seat to adjust the idle as necessary. Optionally, the ECM can be programmed for 800 RPM as the default if so desired.

I have now set the idle to 750 - 800 RPM which raises the oil pressure but did not use the VMSpc to get an accurate reading. The point of my post is to share information that seems important to the well being of the engine and transmission of your coach.
Bob Bowers (Surprise, AZ)
2003 Alpine Coach 40' FDTS
2014 Jeep Cherokee Lattitude
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