I'm planning to have a 370 kilometers road trip between two cities. I want to drive at 90 km/h average speed and without any break or stop. Is it harmful for the engine to run nonstop for about 4 or 5 hours? A petrol engine 4cyl 1.8L 16V.
Automobile engines can tolerate long periods of operation under normal conditions. Extreme conditions such as off-roading and similar racing events subject the engine to more extreme conditions than a long trip on paved roadways.
I have operated a motor vehicle for about as long as your reference figures with zero problems. One aspect of long running I had read about years ago, specific to small displacement engines is to vary the speed periodically.
If your vehicle has cruise control you may want to disengage it for a few minutes every hour to address that consideration. I believe that the caveat of continuous engine speed was for older engines without the benefit of today's high tech lubrication and other sophisticated engine systems.
I've not seen it repeated in recent times.
Periodic stops to rest the driver and perhaps to check engine oil levels are indicated.
Is it harmful for the engine to run nonstop for about 4 or 5 hours?
What would the harm be as opposed to the "harm" by driving if say 1-2 hours at a time, then stopping, the continuing, then stopping, ...?
If you have watched the water thermometer needle in an engine, you should know it doesn't take more than 3-10 minutes depending on the outside temperature for the engine to reach operating temperature.
If the car you're planning to drive has an insufficient cooling system, and it overheats, it would overheat in less than 20 minutes based on the rate of temperature rise. An overheating car would be the only reason you absolutely need to stop periodically in a 370 km trip, and the stops in an overheating car would be so frequent and the cooling periods so long that the trip would not be feasible.
Another reason for stopping might be adding fuel or recharging. Most good vehicles, fossil fuel based or electric, can go 370 kilometers, although an electric car with too small battery might need one recharge.
Yet another reason for stopping might be adding oil, but most manufacturers specify that acceptable oil consumption is about a liter per 1000 km. The dipstick amount between "low" and "full" is typically around a liter, so even with an oil-consuming engine, stopping to add oil is less frequent than stopping to refuel. Besides, most engines in good working condition do not consume practically any oil at all. I haven't needed to add any oil in my current or previous car between the oil change interval.
If you know how the world economy works, long-haul truckers are hauling goods, running their engines for more than 4-5 hours continuously. If letting the engine rest would be good for its health, they would include periodic stops.
The periodic stops are for the driver, not for the engine. The engine likes continuous opreation. The worst conditions for an engine are frequent short trips in cold weather where the engine never gets a chance to heat up.