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Old 02-05-2022, 01:06 PM   #1
Bus Nut
Bon Voyage's Avatar
Join Date: Dec 2016
Location: Calgary, Alberta
Posts: 442
Year: 2001
Coachwork: Thomas
Engine: Cummins ISC 260HP/660Q/MD3060 6spd
Rated Cap: 81
!!!Cummins CAPS 8.3 fuel lubricant!!!

Hi friends, I just wanted to put this out there more prominent for anyone with or looking for a Cummins CAPS injected ISC 8.3. I believe the CAPS injection pump was used in years 1998-2003.

I’ll give the short version here but simply put the pump was made to run on low sulphur diesel but in around 2007 diesel was switched to ultra low sulphur (ULSD). The ULSD has much less lubricity to it which can often cause the CAPS pump to fail. I’ve heard many stories of this pump failure costing many thousands of dollars, some cases $10,000 to repair and leaving people stranded. My own bus is on the 3rd CAPS pump from failures when the school district owned it. There’s more info on this in and other RV forums.

So there are 2 solutions you should be looking at.
1. Add a diesel lubricant to your fuel. I wasn’t doing this until now because the only ones I saw were expensive like Sea Foam, but I recently found a cheaper one that is very affordable. The one I found is kleen-flo and was like $15 for enough to treat 800 gallons.

The second and most expensive is to add a new lift pump that will put constant positive fuel pressure on the CAPS pump. The stock lift pump runs for about 30 seconds at start up then shuts off. Then the CAPS takes over to suck up the fuel and pressurize the injectors. We’ll the CAPS doesn’t do the sucking part very well and when combined with the lower lubricity fuel it fails. Installing a lift pump running constantly will help the CAPS from failing.

Like I said this is the condensed version so if you have any questions please ask.

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Old 02-05-2022, 02:06 PM   #2
Bus Nut
fo4imtippin's Avatar
Join Date: Oct 2021
Location: Jacksonville, FL
Posts: 783
Year: 2003
Coachwork: BlueBird
Chassis: TC2000 28ft
Engine: Cummins ISB 5.9 24v, MD3060
Rated Cap: 14
I use super tech marine 2 stroke oil. 1ounce per gallon. That seems to be the consensus on a few Cummins forums. Basically if your diesel has mechanical injectors, it could benefit from this. Also, diesels don't like being idled because the fuel can wash the cylinder walls, when you add some lubrication to the fuel, it combats this.
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