Just completed a 2,000 mile trip. The hydraulic cooling fan seemed to work properly until the last stop. Traveling in cool weather, engine at normal temp, stopped at a grocery store for 15 minutes. Upon restart, the fan engaged with a roar and stayed engaged until final stop of the day (approximately 15 miles). This has never happened before. The next day all seemed normal as I drove 6 miles to storage. Thoughts?
Heat soak? Did you idle a few minutes before shutdown to cool things down?
I never let it idle a few minutes to let it cool down. It has never engaged high fan at start up, even in hot weather when driven hard.
Coming off a long hot run and then immediate shutdown can cause "coking" of oil at the turbo bearings. If you have been running low and slow for five or 10 minutes under low/no boost before parking less chance of that occurring. If immediately after a long hot run, I idle for at least a few minutes. Better to use high idle under those conditions.
coking oil turbo bearing - Bing (https://www.bing.com/search?q=coking%20oil%20turbo%20bearing&qs=n&form=QBRE&sp=-1&pq=coking%20oil%20turbo%20bearing&sc=0-24&sk=&cvid=EB3EAF95E60A4A89A4E0935FE1C29F4C)
That may (probably is) unrelated to your fan controller issue. I was just thinking the easy explanation would be heat soak of the fan controller.
My understanding is that Cummins recommendations are different than that with the later engines, diesel particulate filters and semi-synthetic oil. I agree with you as it applies to your coach. At any rate, we are getting off of subject. I have driven this coach for 30,000 plus miles and have never had it act like this.
Don't know what controller you have but the electronic fan controllers are sort of notorious for having issues. A lot of people have converted back to the wax capsule type from earlier models, which are supposedly much more reliable. And variable speed, depending on heat load. There's lots of discussion throughout the Forum. You might have a bad electronic controller, which I believe would default to high speed when it's not working correctly?
Currently waiting on a replacement fan controller..spendy buggar..