I am still in the learning curve for Diesel.  I could answere this for a gas engine.  
I just replaced the surge tank on my Patriot 3126.  A previous owner used a 1 gallon bottle of Rotella for the over flow.  He also put extended life coolant (CAT) in 4 years ago.
All that said, why would there be a coagulated oil or grease residue in the tank.  There wasnt alot of it but enough to foul the cap and the fluid.  
There were none of the head gasket type indicators you would find in a gas rig like milky oil and so on.  Just what looks like grease build up.

All opinions are appreciated
Thanks
Keith

A slight amount of oil in a cooling system is not too uncommon. The machining oil used in the manufacturing process on the engine castings is sometimes not totally cleaned out before assembly of the engine and it will show up as oil in the coolant. Also sometimes a little bit gets in the cooling system when a mechanic is not careful enough when servicing the coach.

It will usually be very difficult to totally remove it from the cooling system. So if it is only a slight residue on the cap, do not worry about it, but if it gets worse, it could be a porous block or a mechanical problem that needs to be addressed.    

Gerald

Gerald
The only flush the engine has had ever was 5 yrs. and 20K mi. ago.  The owner did install 500,000 mi. coolant.
The cap was coated inside with what looked like grease but may have been oil goop perhaps from inside the oil jug being used as an over flow.  The used coolant from the tank had small ammounts of grease floating in it.
Here's my question and I would value your opinion.
The grease fitting on the water pump drive bearing has been lubed now twice with about 10 pumps each time.  No grease is visable.  Could this be over greased and the seal inside the bearing is allowing the grease to invade the coolant?  Ever heard of this?


Thanks Gerald for spending time that must become a burden off and on.

Keith

If you look closely at your engine drive belts, I think that you will see that the grease fitting that you mentioned is lubricating the fan bearing only. the water pump is located in a different position, and driven by it's own v-belt and not the serpentine belt that drives the fan. So if your coach is designed like I think, lubricating the fan can not cause grease to enter the cooling system.

The oil jug that is being used as a coolant recovery tank is you probable source.

Gerald

You can have your coolent and oil tested if you like. Usually this is done when you change your engine oil. Just about any truck shop or CAT dealer http://www.catrvclub.org/links.htm can assist.

Keith-

I have to agree with Gerald that the improvised overflow tank is a likely culprit.  CAT indicates that their ELC (extended life coolant) is compatible with most other types unless they constitute more than 10% of the total.  If the previous owner used Rotella ELC rather than plain old Rotella antifreeze, then the carboxylate percentage is likely maintained okay.

One thing you should do is have a CAT facility take a sample of your coolant for Level 2 SOS anaylysis.  Then you'd know if you needed to flush and refill your system due to contamination.  Further information can be gleaned here:  http://www.cat.com/cda/files/87058/7/elcfaq.pdf.

-Joel

Kieth,

This is a guess....The Rotella bottle would not be the anti freeze overflow contaner of choice if one had the time to choose what should be done to replace an existing overflow tank. That would lead one to believe that the overflow tank probably failed while on the road and an expediant repair was made by dumping out what would quickly drain out of the on board Rotella container to complete an emergency road repair.

You could check with the engine manufacturer and see if the coolant flush that they sell contains a reasonable amount of surfactant in it. These products are aimed at removing rust and antifreeze residues so they may not be effective for removing much oil. It would seem like Dawn detergent (good enough for pelicans) and water run through multiple flushes would probably be a good choice if the anti freeze analysis came back unacceptable. I changed my coach over to extended life coolant this spring and did 5 flushes to remove the old coolant. The procedure was to drain, fill, and run at high idle until the temp reached about 120 degrees then drain and repeat. Once the antifreeze is cleared, if you used Dawn, then you would have to repeatedly flush again until most all surfactant has cleared.

I used distilled water for my last flush to start with a base of mostly demineralized water residual to add antifreeze to. I used two gallons of Cat ELC non dilute to compensate for what water would not drain and the remaining was 50/50 ELC premix.

In the old days we had actually flushed motor cooling systems with Spic and Span and we never saw any ill effects. Seems like Dawn would be an acceptable surfactant for a temporary cleaner with less residue than Spic and Span. This is not being proposed as a tried and proven technique so you will have to use your own judgement and perhaps some expert advice might be available from Cat or Cummins tech support on how they would handle this problem.

Regards Ed