Cleaning Up Your Classic Car Engine: Everything You Need to Know

When you own a classic car, it’s easy to spend most of your time keeping the exterior pristine: weekly car washes, regular waxing, touching up the occasional nick and ding, it all goes into a great-looking vehicle. What you might be overlooking (especially if you aren’t a regular car show attendee) is that your engine bay needs just as much, if not more work, to keep it clean where it needs to be, lubricated where it needs to be, and firing on all cylinders (literally!). 

And once you’ve cleaned your engine thoroughly, keeping it tidy can be an excellent way to determine where and when issues are developing: if your motor is getting dirtier in some places compared to others, that could indicate an issue with seals, gaskets or worse. 

But where do you start if you’ve never bothered to pop the hood and take a good look at what should be greasy and what shouldn’t? How can you get a great-looking engine while avoiding damaging something important? Can you just crank up the garden hose and spray away, or do you need to get out the toothbrush and the fine-grit polish? Or is there a happy medium in between? 

Luckily for you, Hagerty knows a thing or two about keeping classic cars on the road in more ways than one. Here are a few tips for getting and keeping what’s under your hood looking as great as what’s above and around it:

Protect the electric, protect yourself

There are a lot of things under your hood that aren’t afraid of a little water. Your electrical system isn’t one of them. If you’re starting a full cleanup, ensure your engine is completely cool. Then take the time to disconnect the battery, remove it from the engine, and you can even grab a couple of plastic bags and cover the alternator and distributor, and tape them down if you want to be extra safe. Also, cover the air intake as well. 

This should cover most of what’s under the hood for electrical systems in a classic car, but if you’re cleaning up anything newer with a more robust electrical system (ie: if you see wiring harnesses in use underneath your hood) take care that you’re not completely drenching it when we get to the rinse. 

It’s also a good idea to make sure that anything that is made to allow fluids to be added to the engine is completely closed. This includes your radiator, your windshield washer reservoir, your power steering or brake fluid, even the dipstick to check your oil - make sure it’s fully shut and secured. 

Once all that is taken care of, since this is likely going to be a messy afternoon, we recommend grabbing some gloves and safety goggles so your hands and eyes can stay free from chemicals and cleansers, plus a dust mask to keep you from breathing in any dirt or debris. 

two cars in garage one with hood open

The Dry Clean: 

No, we’re not taking your shirts or slacks to the cleaners. The dry clean is to get all the dirt, dust and easy-to-remove debris off the engine before you start squirting degreaser on everything and hosing everything down. To do this, you’ll want to grab a brush or three (paintbrush, toothbrush, or other non-metal bristled brushes will do) as well as a vacuum or an air compressor if you have one. 

Start by brushing and loosening up any dirt, dust or other dry grime that’s visible and remove it from the engine using the air-moving product of your choice. Even a few minutes of dry cleaning gets the easy things to clean off the engine and out of the way before digging in further. If you’ve got an aluminum intake or other pieces of large bare metal under your hood, a wire brush or a rotary tool can also be used to clear that off before moving on. 

Spraying the engine before you dry clean it just moves all this stuff around and is more likely to get it stuck further down, so everything you can get off here makes your job easier down the road. 

The Wet Clean: 

Now it’s time to break out the big guns. The first step is to degrease everything: thoroughly cover the engine with a degreasing cleanser which can include a sprayable kitchen cleanser like Lysol or Mr. Clean, an oven cleaner like EZ-Off, an automotive-specific product or even something simple like (the appropriately named) SimpleGreen. Anything that cuts through grease will do, since most of the remaining grime beneath your hood is going to be petroleum-based. 

After you’ve applied your degreaser, wait the recommended amount of time for it to do its de-greasing duties, and then it’s time to start getting rid of all that filth. For everything under the hood that surrounds the actual engine, it’s okay to hose this down and rinse it off, but for the engine itself it’s recommended to simply wipe off the degreaser and taking the grease along with it. Using a toothbrush to get into the tighter areas and in between the ridges of hoses is recommended for the deepest clean, and if you want to pick up a bulk package of microfiber cloths, that’ll get you the best results as compared to, say, old tshirts or worse, paper towels. 

Of note: If these chemicals aren’t the kind of thing you want running into your yard, your street or your sewer system, consider taking your car to a DIY car wash where the system is built to capture that dirty water. Your car and your property will thank you. 

Man looking in car engine

Step 4: Dry, detail and doublecheck

Before you put the battery back in and fire up your ride, grab some more towels or microfiber cloths to clean up any residual dampness and soak up any little bits of standing water. You’ll probably find that this step is still picking up dirt as well, which is understandable: engines are dirty places. If you want to go through once again and reclean everything to get it super shiny, or if you want to really put a high shine and wax on the painted parts under the hood, now is the time.

Now is really the time to take a good, close look at your engine before you shut that hood, though. A thorough cleaning might have cleared out the grime that was covering up growing rust spots, cracks in plastic or rips in wires, or even belt and hose wear. If you spot any damage that poses a threat to the lifespan of your vehicle, handle it now before it proceeds to get worse. And be glad you decided to clean your engine instead of letting that grease continue to build up.

A clean engine is a level of protection that most car owners don’t bother to provide to themselves. Now that you’ve done it once, make sure to keep in the habit of doing it a couple times a year so you can stay ahead of any issues that might be building beneath the hood. 

If you want more protection than just a clean engine bay, Hagerty has a variety of tools and resources to make sure your classic is safe as it cruises to the nearest auto show, off to the autocross track, or even just while hanging out in your garage (perhaps while getting another deep cleaning). 

If you’re taking on a deep clean to get it ready to sell, creating a My Garage page is a great place to have a digital space to list your vehicle, or just to keep an eye on its value to see when the best time to sell might be. 

To make sure your car is as safe as it can be, reach out to a Hagerty agent today to build your custom coverage today.