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How to Keep Your Rig from Overheating

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“I’m melting, I’m melting!”

So said the Wicked Witch of the West just before she magically shriveled her way into history. I’m beginning to sympathize with that cranky lady. At the time of this article’s writing, my state has had a record-breaking summer of wildfires after more than a month of temperatures in excess of 90° F and multiple strings of 100-plus days in the mix. And the calendar says our summer is still ahead.

We need rain.

One of my duties is to oversee the maintenance of a small fleet of six Type III Ford ambulances. They’re all 7.3-Liter PowerStroke Diesel chassies with LifeLine boxes. We’ve hung onto the 7.3s because we don’t generate a lot of miles, and those engines and their TorqShift transmissions have been bulletproof. Just as importantly, the quality of the boxes has supported our continued investments in chassis maintenance. In fact, so far we’ve sent two units back to the factory in Sumner, Iowa, to refurbish and return them to service.

When I was originally assigned to take care of this fleet, we were having two kinds of starting failures. One was an easy fix: We began replacing the batteries annually. The other, which had plagued us for years, was alternator failures—especially of the upper alternators. Of course, the easiest way to correct that would be to switch to Type I ambulances.

One of the disadvantages of a cutaway-based Type III chassis is its teeny engine compartment. There’s not enough room in there for an alternator big enough to supply the needs of an ambulance (or a leprechaun to service it). So Ford resorted to a pair of alternators: one mounted high and the other one low. A Type I chassis has a longer hood, like a pickup truck, that offers much more space. But our garage bays aren’t physicially deep enough to accommodate Type I ambulances. And Colorado’s range of temperatures can reach 110 degrees winter to summer. So you pretty much have to keep an ambulance garaged.

Neither of those alternators is just a spare; if one fails (usually the upper one because of heat), the other will follow soon enough. You can minimize the load on them by switching your emergency lighting from incandescent to high-intensity LEDs. LEDs produce a lot of light with a little energy. Decreasing the load on an alternator should lower its operating temperature, minimize the wear on its drive belt and improve its reliability.

But LEDs require a lot of rewiring, and that’s pricey. You can’t just replace bulbs.

You can idle a diesel all day long, even on a hot summer day with a heavy electrical load (including both air conditionings on full-blast). But when you turn the motor off, the radiant heat of all that metal has nowhere to go. So your underhood temperatures will rise. If the cooling system is in good shape and your coolant is mixed at the proper concentration, it should be OK up to a temperature of almost 300° F. But the underhood temperature won’t be constant. It’ll be hottest up high (like where the upper alternator is) and not so hot down low.

We talked to our friend Cap Unrein at Rocky Mountain Emergency Vehicles (EVMARS) of Denver, who does our maintenance. Cap recommended the basis of the following hot-weather procedure. We leave an ambulance running when we park it outdoors for just a few minutes. Nobody wants to climb into a 120° F ambulance, right? EVMARS installed externally accessible security switches that either lock or unlock all of our doors simultaneously. So we can leave a locked vehicle idling, yet we can access it quickly for a call. Then, when we return to quarters, we turn off the engines and leave the hoods open.

Looks funny. Makes sense. Obviously, we try not to leave the hoods open in public. Our crews don’t post on street corners, and they’re mindful of the temperature-sensitive contents of their compartments, so they normally return to quarters between calls. And we don’t know yet if this will even work. But it makes sense for any vehicle, whatever its design. And in this heat, we’ve gotta do something.

I have to tell you, there’s one more component to this plan. The crews have to understand their instruments—and the mechanics of their vehicles—well enough to make it work. To my way of thinking, that requires training and experience.

Neither of which happens by magic.

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