When heart specialists put a new engine into an old Maxwell body, they tell the customer to drop by occasionally for monitoring. Wednesday it was time for my 6,000 mile checkup, so my copilot and I drove up to New York University's Medical Center.

While I was with the doctors, my wife had an opportunity to take inventory at several department stores and find out whether they stock any items not carried by their Washington branches. It turned out that they do, alas!

But I disgress. I chose to drive up this time because I wanted to check on two points: Was Charles Kuralt right about truck drivers? And is the 55-mile-an-hour speed limit really being universally ignored?

One round-trip of less than 500 miles does not provide an irrefutable basis for forming an opinion about nationwide driving havits. However, what little I saw indicated that there are few people on the highways who drive at a steady 55 miles an hour.

Some, for example, think 40 or 45 is a nice rate of speed. The "pace" favored by most is usually between 58 and 60, not only for pleasure cars but also for trucks that can maintain such pace. On upgrades, many trucks can't go as fast, but most pleasure cars, which could remain at a steady speed, also slow down because their drivers fail to compensate for the upgrade.

Some vehicles move at 65. Now and then somebody flashes by at perhaps 70. But if you see four or five like that during a four-hour journey, you also see four or five pulled over by troopers who are writing tickets. The biggest difference between truckers and other drivers appeared to be that scofflaws in trucks were more noticeable. The bigger the vehicle, the more villainous the driver, or at least so it seemed.

Another point about going to New York by auto is worth mentioning. On the Maryland portion of I-95 (the John F. Kennedy Memorial Highway), regular gas is 64.9 cents a gallon. On the New Jersey Turnpike, the same gas is 60 cents a gallon -- 4.9 cents a gallon cheaper. On a tankful, the saving is around a dollar.

If you arrive at the Lincoln Tunnel with two quarters in hand to pay the toll, you'll get a jolt. The fee to enter New York by tunnel is now $1.50.

However, they don't charge you anything to leave, so the actual cost can be stated as 75 cents each way -- a mere 50 percent increase over the old rate. What's 50 percent these days?

As soon as you emerge from the tunnel into Manhattan, you'll be struck by the snow and the huge mounds of trash that line most streets. My mind went back to a reader's explanation many years ago that if a combination of smoke and fog is smog, then a combination of snow and dirt is snirt. Manhattan now needs a new word -- perhaps "snash."

At dinner that evening, Bob Wolff and his ever youthful Jane informed us that city authorities had explained to New Yorkers that snow and trash couldn't be removed at the same time, "so the trash just had to pile up and wait." And boy, is it ever waiting! I heard one newscaster mention 80,000 tons, but he must have been talking about one specific street.

As you move across the island from west to east along 42d Street, you see theater marquees that proclaim "Live Sex Acts On Stage" and describe a variety of even more depraved entertainments available inside. The visitor is left to wonder whether 42d Street's porno industry isn't dirtier than its combination of snirt and snash.

We finally reached a clean environment at the NYU Medical Center, where several eminent doctors told me the engine is running fine and I shouldn't even think about retiring. I didn't accuse them of a conflict of interest, but I happen to know how they feel about people who help raise money for hospitals. They're not about to let me waste my time playing golf.

As a young doctor prepared to listen to my heart (NYU is a teaching hospital), I remarked that at times one doesn't need a stethoscope to hear the plastic valve they gave me. "My friend," the cardiologist commented, "the time to worry is when you stop hearing it."

I suppose a quick way to summarize the report I got is: If I die of anything in the near future, it's not likely to be heart trouble.

The engine doesn't purr; it sounds more like the "slap" of a diesel. But it works, and that is more than can be said of my brain on some mornings.

Perhaps I should have asked them whether they also do brain transplants.