Will an ambulance be damaged by turning its engine off at the ER?

Dear Car Talk

Dear Car Talk | Dec 01, 2002

Dear Tom and Ray:

Please help me settle a long-standing problem concerning diesel engines and ambulances. I'm an emergency physician in Bowling Green, Ky., and I am now at the center of a major controversy, which I started, of course. I can't convince the paramedics that it is OK to turn off the engines on their ambulances after they back up to the doors of the emergency department. I insist that the engines be shut down because I choose not to become ill from the overpowering fumes.

The excuses have varied over the years and have included "them diesels will lock up if you shut 'em down right away," and "the turbochargers run so hot they will burn up if you don't let 'em idle for 15 minutes before turnin' 'em off."

Statements such as these have led me to marvel at the fact that the universal laws of physics and thermodynamics do not apply to diesel ambulances. I have researched this subject with calls to the engineering department at Ford Motor Company, as well as the ambulance manufacturer and several diesel truck mechanics -- all of whom say "no problem, turn them off." The opposition has not been able to produce any owner's manual, service manual or other document indicating that anything will burn up or lock up. In my 20 years in this business the only thing that has come close to being locked-up is me. Recently a couple of paramedics from a not-so-neighborly neighboring county called the police to have me arrested and "locked-up" in jail for "touching" their truck after I went outside and turned off their ambulance. I never meant to harm anyone's diesel.

In retrospect, I don't know what came over me. Toxic fumes, perhaps? Your thoughts on this matter would be appreciated. -- Gary

TOM: Well, let me start by saying that there are certain people whose bad side you don't want to be on. Your food preparer is one. The guy pulling you out of a burning wreck is another. But you don't seem like the type who responds to appeals for diplomacy, Gary, so we'll just answer your question.

RAY: Fifteen minutes is a gross exaggeration, but turbocharged engines generally do require a brief "cool down" period.

TOM: When the turbo is run hard, it gets very hot. And if you turn the engine off before the turbo cools down, the oil inside the turbocharger's tiny oil passages can "coke" or dry and harden in place and ruin the turbo. But if you let the engine run for a minute or two, the turbo cools off (relatively), the oil drains down, and everything is fine.

RAY: And in fact, Navistar, who makes the engines for these Ford ambulances, says that under most driving conditions -- even emergency driving -- the engine doesn't need any cooling off period before it can be shut down. But when the engine is run under full load (at very high speeds or up a long incline), it should be idled for 45 seconds to two minutes before being turned off.

TOM: So your drivers are correct, in theory, Gary, but they are being overly cautious. And they also hate you.

RAY: Right. So you'd be well-advised to let someone else do the negotiating at this point. But perhaps after a minute or two, they'd be willing to shut off the engines and spare everybody a couple of lungfuls of diesel exhaust. Unfortunately, in most cases, during those two minutes, you, your staff and the incoming patient will still be the ones most exposed.

TOM: So another solution would be to have the hospital install flexible exhaust tubes, like we use in the garage. We often have to run cars inside the shop to diagnose them. And we have hoses that hang down from the ceiling. They slide onto the exhaust pipes of cars, and they take the exhaust out of the garage, so we don't get any dumber than we already are. If you had a couple of them hanging there, you could slap one onto the exhaust pipe as it backed in, and everybody would be happy.

RAY: Just be careful they don't reroute the other ends of the pipes into your office, Gary. These guys are out to get you.

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