1. ## Engine Hours Conversion

I'm in the beginning stages of pulling some data together for a small research project for my organization regarding the rate engine hours are accrued compared to actual miles driven. The intention is to analyze the data to see if the preventative maintenance program needs to be adjusted to meet the demand placed on the fleet of ambulances. I'm seeking some guidance and answers from everybody.....

Is there a formula to to convert engine hours to miles? A mechanic at our local Ford dealership reports Ford suggests the multiplier for engine hours to actual miles is 33. A mechanic at our Freightliner dealership tells me to take the miles per hour the ambulance is traveling at 1200 RPM (Our high-idle engine speed setting) and use that as the multiplier for engine hours. Then subtract the actual miles on the odometer from the hours conversion to get an accurate number of miles. Is this correct? Is there an industry standard?

How many of you use engine hours instead of engine miles to calculate when preventative maintenance is needed? (Oil Changes, Fuel Filters, Air Filters, Belts, Etc...)

2. 33 is the number I've always used. I abstracted that from my trucking days. I watched the odometer and hours counter on one of my F-model Macks for a period of time, and that's the number that I got. There are variables that could change it. When I send oil samples in for analysis I report in hours rather than miles. I also record both in my maintenance records.

Some fleets with irregular operations use gallons of fuel consumed rather than miles or hours as their PM interval marker.

3. Kyle F M: A whole lot of the equipment in the fire service never sees more than 5 to 8 thousand miles per year. Big problem then is short runs with moisture build-up in the crank case and other places due to a lack of temperature rise suffient to drive off the water & volatiles. Over-the-road equipment frequently is on a 40,000 mi schedule because of the type of usage. Thus an annual maintenance program on much of the fire service equipment is more than adequate. Engines (older) that used the drive line to power pumps, also rolled the odometer when pumping, thus the odometer reading included all of the pumping time, but not the high idle time when powering a PTO generator or hydraulic tool. Check the road speed in high gear at the high idle speed on the tachometer. Say 1200 rpm, then use that speed to determine the equivalent road miles. CE11 is pretty close for a Mack where idle is 500 rpm and the road speed would be around 15 mph. Powering a Watrous pump generally needs about 1100 rpm to reach 150 psi, and this would be almost exactly 33 mph. Some of our more recent engines disable the odometer when the pump is in gear, and the rpms are a little higher when running 180 psi (1350) but it is in "Direct" (4th) instead of 5th (Overdrive). With the ambo, I would do what was suggested (check the high idle rpm) then check the MPH at that rpm in high gear. Use that number to determing the equivalent miles for maintenance purposes.

4. Thanks for the gentlemen. I just wanted to verify my train of thought was correct.

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