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Engine cool down

After coming to a stop, either pulling off the highway, or city streets, would it be in the best interest of an engine's longevity to let it idle for a few minutes to gradually cool down? Thermal expansion and contraction can have detrimental effects on engine components as the thermal expansion of steel is different than that of cast iron or aluminum.

Example: Ford 460 V8 engines in older rvs would and did snap exhaust manifold bolts if not cooled down.
Nitehawk,  Demolition Lady, & our NEW master, Zippy the speeding BB cat.
1989 Grand Villa 36' ORED
Oshkosh chassis, 8.2 DD V8
2006 Saturn Vue AWD

Re: Engine cool down

Reply #1 –
Yup...Cool-down is needed for the turbine as this is what gets very hot during long periods of high horse power demand.  In most cases if you are pulling off the highway after a long climb, by the time you reach the area you will be stopping at, the cool-down has already occurred.  The ambient temperature may also contribute some to the cooldown requirements.  e.g.  If you're stopping when the outside temperature is -15 F, then the cooldown needs to be longer as the temp. gradient is much greater as the ambient temp. gets lower.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Engine cool down

Reply #2 –
I use a 20 minute rule..If my stop is less than 20 minutes I don't shut down. I always let her cool down a few minutes before shutting  if over 20 minutes.. You will get many different opinions.
We are only strangers until we meet; however, some of us are stranger than others

Re: Engine cool down

Reply #3 –
Cummins' recommendation is 5 minutes cool down maximum, and that is only immediately after a major pull.  As has been already said, normal maneuvering after leaving the highway is adequate cool down. 
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Engine cool down

Reply #4 –
I agree with the "other Brett".  Both Caterpillar and Cummins recommend a max of 5 minute cool down-- and that is only if you have been working the engine very hard just before you stop.

If you exited the highway, drove a few blocks at low speed and pulled into a CG, 2-3 minutes is all that is recommended.

I suspect Detroit Diesel's recommendations are the same, but have not worked with them on this.

Brett Wolfe
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Engine cool down

Reply #5 –
If I pull off the road in a rest stop I do not shut down if it is just a break to walk the dogs or to grab a quick bite. If I pull into a campground the same thing. I will shut down in my space. It is usually only a couple mins. If I pull in at home after running 6 miles on surface streets I shut down right away. You only need  five mins max to cool down and silverleaf shows it happening too. I just do not want to have to trouble shoot starting if an issue presents itself in the entrance of tbe campground or the middle of the fuel pumps. 
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Engine cool down

Reply #6 –
Quote from: nitehawk –
After coming to a stop, either pulling off the highway, or city streets, would it be in the best interest of an engine's longevity to let it idle for a few minutes to gradually cool down? Thermal expansion and contraction can have detrimental effects on engine components as the thermal expansion of steel is different than that of cast iron or aluminum.

The definitive reply is contained in your Operation and Maintenance manual for the engine.
The guidelines are set for extreme conditions such that the engine is protected if one follows the guidelines.

Your engine will last relatively longer or shorter depending on how well you abide by the suggestions in the O&M manual.
If it's not severely cold out and you're using high quality, clean 15W-40 engine oil or 10W-30 below 70 deg. F, you may start the engine, let it idle for 10-15 seconds and slowly drive away (at modest power levels) with no ill effects.

If running hard or pulling up hill, the engine may need to be run as long as 5 minutes at idle to uniformly cool internal components and reject heat away from turbo bearings; running slowly off the Interstate ramp and driving at low power levels to the fuel stop counts for some of this time, but if running on the highway, it's a good idea to idle for a couple of minutes before shutting down.

Cummins does NOT recommend excessive idling of the engines, since it can cause excessive carbon buildup on the pistons, piston rings, injector tips, valves, etc.

Over-the-road truckers and bus operators keep their engines running to keep the heaters and/or air conditioning going, however, they run the engines up to about 1200 rpm or so and that will usually keep the coolant temperature in the 140 to 160 range. It still is not recommended by Cummins.

The belief that idling the engine is better than shutting it down is also a myth.
Idling is not within the manufacturer's predetermined RPM and load range for maximum performance and best fuel economy.

When idling unnecessarily, incomplete combustion occurs that causes over fueling.
Under these conditions, combustion gases and fuel can enter the crankcase, cause deterioration to the oil additive package, and eventually cause premature engine damage.

What are Some of the Problems Associated with Idling?

Idling Wastes Fuel and Money

• A typical truck burns approximately one gallon of diesel fuel for each hour it idles.

Idling Causes Excessive Engine Wear
• Running an engine at low speed (idling) causes twice the wear on internal parts compared to driving at regular speeds. According to the American Trucking Association, such wear can increase maintenance costs and shorten the life of the engine.

Unnecessary Idling Causes Pollution
• Idling vehicles can emit significant amounts of pollution including: carbon dioxide, which contributes to global climate change; nitrogen oxides and volatile organic compounds, both of which contribute to the formation of ozone smog; poisonous carbon monoxide; and particulate matter.

Idling Poses Health Risks to Drivers
• While sitting in an idling vehicle, drivers are exposed to the vehicle's pollution more so than when the vehicle is in motion since there is no air flow to vent the emissions.
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"

Re: Engine cool down

Reply #7 –
Barry, I agree with everything you said.  If I am going to stop for a long time I shut down but if I will move again in five or ten minutes I will let it idle. I will be able to keep the dash air or heat going or keep the batteries topped off. In fact I idle till I am plugged in so my charger ilk not see a low state of charge on the house batteries and start in bulk charge. In fact when you bring a bunch of FT into a park at the same time you can overwhelm the parks electric. Not perfect but I do put it in high idle when sitting for more than five mins. 
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Engine cool down

Reply #8 –
The cooling down for a turbo diesel is because the turbo is extremely hot and causes the oil to coke the bearings of the turbo.  That is not good for the turbo, thus cooling down the oil and turbo and that makes the expensive turbo last much longer.  Like Brett said, just taking it easy after exiting the highway is all that is needed.
1994 U225
build #4514