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Dear Tom and Ray: I’ve got a question that arises from time to time in my office. Often, we need to visit faraway cities and towns within the state for meetings and the like (and long lunches). They give us two options: We can get a per-mile reimbursement if we use our own car, or we can rent a car. I know that the reimbursement allowance is to cover wear and tear as well as gas, so how do I value said wear and tear? – Kyle

Ray: I would always rent a car, Kyle.

Tom: Sure. Most companies, and the federal government, will reimburse mileage at 55 or 60 cents a mile. That’s supposed to cover gas, as well as wear and tear on your car.

Ray: But trust me, you’re not going to make money on that deal. At best, you’ll break even. Every year, the IRS calculates the average cost of owning, maintaining and repairing a car, and divides that by the average number of miles driven to get the mileage reimbursement.

Tom: And sure, it’s nice to get that reimbursement check now, because it’s always more than you spent on the gas – so it seems like a windfall. But that’s money you will need for future repairs, and you’re essentially borrowing from the future of your car.

Ray: Plus, there’s some wear and tear that can’t be calculated. What if Selma the slob from sales spills her venti skim latte on your front seat? What’s the mileage reimbursement for a big, brown stain and sour-milk odor?

Tom: Or what if 350-pound Bruno from marketing yanks off the door handle because he’s an animal?

Ray: Or what if you have an accident? Sure, you probably have insurance to cover the cost, but what about the deductible and the inconvenience?

Tom: Whereas if you use a rental car, I can guarantee that there will be absolutely no wear and tear on your car. Plus, you get to drive a reliable, new car that your kids haven’t turned into a rolling junk pit yet. That’s how I’d roll.

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Dear Tom and Ray: Is it safe to add a few capfuls of denatured alcohol to the crankcase of my two older vehicles to remove oil sludge before I change the oil? – Lorilee

Ray: Is it safe? Well, I don’t think it’s ever a good idea to dilute your oil. But you can put a couple of capfuls of almost anything in five quarts of oil without doing a whole lot of damage. I mean, you can add a couple of capfuls of cat urine to your crankcase and still drive the car for a long time. The question is, Why would you want to?

Tom: The same question should be asked of denatured alcohol. I don’t see a good reason to do it.

Ray: First of all, while denatured alcohol is a solvent, we have no idea whether it does anything at all to remove engine sludge.

Tom: Second, we don’t even know if you HAVE excessive engine sludge. Did your mechanic tell you that your oil is not draining down quickly enough from the top of the engine? Or do you just have S.A.D.: sludge anxiety disorder?

Ray: Unfortunately, even if you’re sure your engine is sludged up, it’s unlikely that any oil additive is going to fix it.

Tom: We work on Volvos that develop sludge problems sometimes. What happens is that the crankcase ventilation system gets plugged up and doesn’t allow oil fumes to be purged from the engine. So those fumes get trapped and solidify, forming sludge and gunking up the top of the engine.

Ray: At that point, the only way to remove the sludge is to remove the valve cover and actually scrape off the stuff.

Tom: If you’re wanting to add the denatured alcohol simply as a preventative measure – if you’re worried about getting sludge in the future – then the single best thing you can do is change the oil regularly instead and make sure your crankcase ventilation system is working properly.

Ray: Save the denatured alcohol for cleaning your windows. And on those nights when you toss and turn, restlessly worrying that sludge is somehow building up inside your valve train, get up and change the oil, then go back to bed.

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