Bottom Line
Maintenance Q & A
Optimizing oil integrity

By Paul Abelson, senior technical editor

Q. I have a Cummins N14 with a rocker box gasket leak. I was wondering if you know of any good products I could use in the engine coolant to seal the leaky gaskets for now – ones that won’t hurt the engine.

A.  I’ve learned at TMC that it’s better to fix the cause of a leak than to add chemicals or plug leaks with gum or fibers. They just mask problems; they do not fix them. Even worse, they can cause secondary problems. They’re fine in an emergency, but only to get you home. If you must use them, plan to do a permanent fix as soon as possible.

A bigger concern is that you mentioned coolant with a rocker box leak. Rockers work in oil, not coolant. Did a dealer or repair shop tell you that coolant was leaking at your rockers? Did you yourself see coolant there?

I consulted with my Land Line colleague Jeff Barker. He has far more hands-on time inside engines than I ever will. Jeff agreed that rocker arms are lubricated (and cooled) by the engine oil.

There should be no coolant flowing anywhere near them other than through the cylinder head below. If it has mounting bolts for the rocker arm bases that go into the water jacket at the head and if coolant is passing into the oil at that point, you need to reseal those bolts immediately.

You should also look for cracks in the head at the bolt holes. There’s no way that adding anything to the engine coolant will seal a rocker gasket. There is also the possibility you may have a leaking head gasket.

“If coolant is getting into the oil anywhere,” Jeff said, “he runs a serious chance of destroying the bottom end of that engine. I’m no fan of putting BarsLeak or anything similar into a cooling system. Those things can clog coolant passages in oil coolers and radiators. It’s always less costly to fix it right the first time, before he ends up with more serious engine issues.”

Q. I’ve read about extending oil drain intervals because oils are getting better. I have a 2001 Western Star with a Cat C15 motor. I change oil at about 15,000 miles give or take a thousand depending on where I am. I prefer to get to a TA for oil changes because they do a thorough inspection. The truck has nearly a million miles with no major problems other than injectors.

I heard about people changing at 30,000 miles. Can I safely extend that far? If not, how much can I extend?

A. You are correct that oils have improved greatly since your engine was built. Driven by emission-reducing technologies, CI4 and CI4 Plus oils were introduced to manage higher levels of soot in oils, in time for the October 2002 introduction of exhaust gas recirculation (EGR) to lower nitrogen oxide.

The EPA targeted particulate matter in 2007, and engine makers needed oil to suspend more soot and to hold it in suspension even more tenaciously. The industry came through with CJ4 oil.

Today’s oils (both are considered current) will keep your engine cleaner longer so you can extend your interval. If your oil analysis has shown that your oil is good, wear metals are low, and total base number (TBN) is higher than total acid number (TAN), I would be comfortable recommending an interval of 20,000 or even 22,500.

Beyond a 33 to 50 percent increase in intervals, I would go through an evaluation according to TMC’s Recommended Practice RP334, Guidelines for Establishing Proper Engine Oil Drain Intervals for Heavy-Duty Diesels. It calls for taking samples between changes and plotting results. It will let you project when the oil will need changing. LL