Diesel Idling

Firstly, let's define the term. We are talking unloaded, static idle (500-650 RPM) ­ like you can see at any truck stop or freight dock, bus garage, construction job site, fish harbor, even rail yard, or tug yard. There they sit, all day, maybe all night long - 10 below, to 115 degree days, hour after hour - idling.

Whether it is a Detroit 2 cycle, or other 4 cycle is immaterial, it is part of the "tradition", the folk lore, the "everybody does it" thing, you sleep and keep warm, or run the air conditioner, go eat, or wait to get loaded, or move on the next pile - attended/unattended - just let it idle. "Never shut a diesel down". I had more than one fleet manager proudly announce to me (emphatically) that "our engines are never shut down-except to change oil or repair". A Greyhound shop manager proudly showed me three starters on the floor that were just rebuilt and proclaimed, "next time we do filters we have to put those starters back on, of course our units are NEVER shut down, so it doesn't really matter !"

Let me bore you with "my" perspective:

We can start maybe during the 1930’s. Diesel engines were simple, and we really knew little engine-wise. Engines were primitive because of the materials we had available, our machining/fabrication abilities were ungroomed, and our storage battery situation was "comical" (wood cases/tar/ low voltage, what’s a cranking amp anyway ?). These balky engines barely knew what an "atomized" spray was. Fuels were, well, fuels, and engines still had torching grids or crosses cast into them for torch heating, pony motors were everywhere (you took them into your motel room), and charcoal tray oil pan holders were commonplace. Gasoline on a rag and ether bottles, primer valves and spark plug fired gasoline blast intake manifolds, propane, and compression release devices of many "wild" designs, tow hooks mounted on everything, and even truck-mounted, super heated alcohol/coolant pump rigs (that was our anti freeze back then) to drain cold and refill hot.

On any given morning, just getting started was a tribulation. In the Antarctic, St. Louis, or the hot deserts of Mexico, once started (if you got it started), never shut it down.

Even after a half day's work, given a few hours off, a restart was no guarantee without a fight.

For all of the diesel engine improvements, after WW II there was very little changed. When trucks began cross country routes and diesel became part of our "lifeline", things slowly changed. By the mid 1950’s we had developed decent storage batteries and electrics, and engines were much more sophisticated. Fuels were optimized and constant, and we had cold start aids that worked. Times had changed.

I have to say, that by the 1960’s, essentially diesel "things" were about like they are today, automobiles and diesel trucks were safely "stop and go" entities. (other than the usual poorly maintained, junkers, and obsolete rigs that always exist), what we knew back then was virtually what we know today.

DO NOT IDLE YOUR DIESEL !

There, I said it !

I attended months of factory schools on Hercules, Detroit Diesel, and Cummins, then later went corporate with bigger engines, but the knowledge was the same - universally. During the 1950’s cam ground (gas/diesel) piston designs came into vogue, measuring a room temperature piston was a shock! It was not round, and it was not the same dimension top to bottom, those clever designers were tired of fighting over-temp seizures and start-up chaffing, so they designed pistons to not be shaped like pistons until they reached around 140 degree water temperature. Lay your micrometers on a hot piston and it "was" what you expected.

At below 140 degree water temp things went backwards though. As the piston returned to its cam ground specs it allowed air and fuel to sneak into the crankcase, and the piston itself, now not fitting the bore, sorta’ wobbled. In doing so, it made the rings chatter, and with the added air and fuel residues things were not good in cylinder-ville. Issues on block expansion, gasket pinch, and lube oil adequacy all played in at lower temperatures as well.

These phenomena were much enhanced on a diesel vs. gasoline engines. Firstly, diesel is just a heavier, less evaporative fuel. Lower air flows impair atomization, diesel fuel likes engine oil, and diesels over-cool the combustion chamber (no throttle butterfly, higher capacity cooling system) anyway.

As a warranty guy, I could tour truck stops and see rigs in Bozeman, Augusta, or Fairbanks at 06:00AM with a lake of raw fuel and oil underneath, having seeped through the pipes and overflowing the dipstick tube from an over-full crankcase on still-idling trucks. Water temperatures at unreadable gauge bottom (60 degrees) was more than common, 90 degrees was a hot one! If it broke 100°, she was a scorcher.

Oil samples taken were dilution disgusting, yet the driver would wake up and hit the road for a 300 mile power jaunt. Turbochargers were coming into vogue, and engine clearances and tolerances were getting pretty tight. We had "O"-ringed liners, and cooling systems that caused aeration pitting. Our fuels were "cut" in winter, and the times and machinery had simply changed, the excuses and reasons for idling were now in all the past, obsoleted, and non-applicable.

I was leaving Chicago late at night, for Cleveland after one of those 12" Chi-town snow storms hit quickly and locked the city up. As I stumbled into Gary, where the truck stops are kinda grouped, all the lots were full of trucks, thousands who had gathered there at dusk when the ugly started falling. At 2AM it was cold, and white. White smoke I mean, the place looked like a hot tub in Minnesota! As I parked the air was heavy and actually oily, the smell was really severe. As I walked through the rows and rows of rigs, I wondered how the sleepers did not smell this borderline noxious unburned fuel vapor. In 1965 there were three big Gary area stops, I went to all three.

I had seen a couple of our "house account" company rigs in there, so I took the time to call them for a scenario the next day. At 4PM most had beugan assembling after the word got passed to get off the road. By 9-10 AM the plows were done and things began rolling again. 18 hours of idle.

I began addressing this issue with our test cell and shop people, then reviewed teardown histories/stories/theories, and spread the word to our shops for the next day after the storm. New arrivals to our shops were checked for dilution (dipstick filter paper) and I accumulated the test sheets (Shell oil had a test kit out back then). The next spring, I reviewed and assembled all this info into a paper.

I learned that as long as the water temp stayed above 140, idle your heart out! Once below that, or into white smoke, fuel-oil dilution, turbo damage, piston score, bottom end squeaking, and shortened engine life were imminent. Plus, there goes your warranty.

Diesel engine companies were all fighting the same problems in the mid-1960’s, idling was one of them! Secure hand throttles could hold your RPM to turbo cut-in point, or cylinder temperatures where the coolant did not drop below 140 especially with winter fronts/shutters and the sound deadening on a modern truck. But this meant you were up around 1,000/1,100 RPM, and as ambient temperatures changed, a hand throttle was not a very stable thing.

With residents complaining (firstly about diesel smoke, then engine noise) truck stops started adding plug-ins for engine heaters, the mantra at all the factories was in unison though, "Do not idle at temperatures below 140 degrees". My co-trainer friends over at Detroit Diesel, and Caterpillar told the same story as we did at Cummins, we all had a problem!! Stewart-Stevenson down in Texas did a big write up on DD idle problematics - I wish I still had a copy. It was written in oil field language and perhaps more severe than even the "factory" stance on idling.

I can remember to this day, in conducting driver or mechanic classes, the blank looks on the faces when I would say "One more time, do not idle a diesel UNLESS you keep the water temperature above 140 degrees! There are no exceptions. This is not 1948."