Would you allow your car’s engine to be washed together with the rest of the car’s body? The answer is:

NOOOOO!!!!!!

YOU’RE GOING TO RUIN THE ENGINE AND ALL ITS ELECTRICALS, AND THE WORLD’S GOING TO END TOMORROW!!!

That’s what an alarmist would say. If you look closely at the components in the engine bay, though, you’ll notice that the electrical connectors look a bit different from those of cars built over a decade ago. A majority of vehicles–not all, as there are still some vehicles out there that use the older-style electrical connectors from the ’80s and the ’90s–now use what’s termed as “weather-sealed” connectors.

You’ll also notice that the ECU is in the engine bay. Which means it is going to be weather-sealed as well. No, it’s not waterproof, but it will withstand a certain amount of moisture before water gets in. If anything, there’s more risk of water breaking through the weather seal of the connectors via the droplets of water coming from a pressure washer that’s going to be used to rinse off the foam. However, the pressure washers used by car-wash and detailing establishments will unlikely be forceful enough to penetrate the seal (at least not from the distances or angles that the spray nozzles are usually oriented at).

You’re more at risk of damage when you foolishly decide to drive your car through flooded streets. Not to mention, of course, that foam applicators also operate at much lower pressures than a pressure washer.

On a newer car with “hardened” electricals, things like that won’t hurt much, but you’re not doing the engine bay any favors either given that there are other ways to keep an engine bay clean–clean, not shiny. Personally, I’d forgo the engine wash and instead use a clean rag, a duster or some compressed air to blow off the dust in the engine bay. Or go to a waterless engine detailer, which happens to conserve water, too.

Occasionally, I might use a pressure washer on an oil-caked engine to cleanse off the grime that has built up on certain parts of the engine–parts, for instance, that have an oil leak that I need to track down. But even then, I’d be more likely to use a commercially available degreaser that’s more suited to the task before aiming a pressure washer at the engine.

In other words: An engine wash should merely be plan B, to be used only if absolutely necessary.

Keep in mind as well that, in general, anything that you apply to a car’s surfaces that’s got a slippery and greasy feel to it–while looking clean initially–will tend to attract and hold on to dust and dirt more than if the surfaces didn’t have any “protectant” or “product” applied.

How to do it

There are practical reasons for removing a gross accumulation of grease, oil, fuel, and dirt from under the hood and for making an effort to keep things under control from then on.

Most engines are made of metal and depend on rubber hoses, gaskets, and wiring if they’re to work properly. Because all the aforementioned baddies can seriously deteriorate nonmetal parts and wiring, keep the under-the-hood area as clean as possible. If it’s beginning to look grubby, get a rag and wipe off as much of the dirt and grease as you can without removing or moving hoses and wiring.

Never use a hose to wash under the hood — the water can ruin the electronics. Have your engine cleaned professionally if it’s too dirty to wipe clean yourself. When the job is done, you should be able to keep it in good condition by simply wiping off the area every now and then.

If you’re planning to sell your vehicle, think twice about having the area under the hood cleaned. Although cleaning certainly spiffs it up, potential buyers may assume that it was done to obliterate signs of unsuccessful surgery on the engine.

Whenever you clean under the hood, make sure that you clean the blow-by on the inner surface of the hood, too, and that you remove the mud and dirt that have accumulated on the inner walls of the car’s body and near the wheel wells.

If you find that oil accumulates very quickly on your engine, first check the PCV valve to see whether it’s plugged up. This little gadget is responsible for rerouting the exhaust fumes from the crankcase back to the engine, where they’re burned again and then released through the exhaust system. If the valve gets plugged, pressure can build up in the crankcase and create oil leaks around the engine. A PCV valve can be checked and replaced very easily.

Oil also may seep from under the valve cover gasket if the cover needs to be torqued down properly or the gasket needs to be replaced. If this seems to be your problem, check with a mechanic.