Guest Contributor: Craig Fitzgerald
These days I write a lot of auction listings for one of the vintage car auction sites. It’s great because I get to comb through dozens and dozens of photos of around 30 vintage vehicles each month, and learn more as I go.
Over the last almost four years of doing this, the biggest thing I’ve learned is that most people clean what they see and ignore the engine bay. A lot of great-looking cars come through my laptop every month, and the vast majority have dirty engines that could use a little sprucing up. When it’s time to sell your car, you can be losing hundreds, even thousands, of dollars by not focusing some attention on how clean the engine bay is.
Why Should You Detail Your Engine Bay?
Aesthetics are the primary reason most people are detailing under the hood. Whether you’re getting ready to sell a car or just enjoying it yourself, opening the hood on a freshly detailed engine is a visual pleasure.
But the process of detailing an engine bay also helps you identify leaks that should be addressed. If you’ve got a leaky valve cover, it’s going to become immediately evident the second you get started cleaning under the hood. Weeping seals tend to collect dust and turn it into a sticky black concoction, masking underlying leaks that should be corrected.
It also gives you an opportunity to inspect consumable parts like upper and lower radiator hoses, heater hoses, and belts for signs of wear. Any cracks in the hoses will become immediately obvious as you’re cleaning, and it’s a great chance to swap those parts out before they make themselves known on a long trip.
Finally, it gives you a chance to inspect your battery terminals. Is there a froth of corrosion attached to your positive terminal? Corrosion on your battery terminals can be the cause of battery acid reacting with the positive and negative terminals. Sulfation can also cause a grayish buildup on the terminals. For more on how these issues can impact your battery performance, visit Yuasa’s web page on the topic.
Pressure Washing Your Engine: Is It Safe?
Usually, when car owners start thinking about cleaning their engine bay, their first thought is to use a pressure washer. Pressure washers use an electric motor or a gas engine to force water out of a nozzle at a higher pressure than a typical garden hose. While that can be helpful in removing grease and grime, it can also cause as many issues as it solves.
The era of ignition points and distributors is long behind us, so we’re not so concerned with getting a distributor cap wet, but there are loads of electronic components, sensors, and wiring under the hood. They’re sealed and generally weather resistant, but pointing a jet of water coming out of a nozzle at 3,000 PSI at your ECU probably isn’t the best idea. Even valve covers can be vulnerable to water intrusion when you spray them with that much pressure.
You can use a pressure washer to clean the lower reaches of an engine block, but in a modern car, those lower reaches are generally invisible, anyway. In general, the pressure washer is better to use on the underbody and suspension components. We’re fans of more gentle methods of cleaning.
How to Clean Your Engine
Think about the area you’re about to clean before you even start. In a modern vehicle, the first thing you see when you lift the hood is a plastic engine cover. That piece is easy enough to remove and clean outside of the engine bay, but there’s a lot of additional plastic under the hood on things like fan shrouds, radiators, and even inner fenders, so you’ll want to address those items with a cleaner that’s safe for use on plastics.
Under that engine cover are all of the more sensitive components that deliver spark, fuel, and air to your engine. Those components are generally some kind of metal, either steel or aluminum. Intake manifolds and valve covers can also be plastic. What you’re trying to remove from those surfaces is generally oil, grease, and the dust that accumulates on it.
There are plenty of foaming engine cleaners on the market, but that may be a little aggressive for a modern vehicle. You can often get away with a simple, non-toxic solvent like Simple Green or Purple Power in a spray bottle. One of our favorite underhood cleaning supplies is – as crazy as it sounds –Totally Awesome Carpet Cleaner, which does a great job of removing grease and grime while not leaving a lot of residue behind.
Just like washing your car, you want to start with the high points and work your way down. That includes the underhood. Nearly every car has an insulating mat under the hood. If yours is in bad shape – with pieces of insulation falling – take it off and get a new one. An OEM insulation pad for the most popular vehicle on the road (a 2017 Ford F-150) runs about $75, and if yours is in tough shape, it will make all the difference in how your engine bay looks. If it’s in good shape, you can usually carefully vacuum the mat to remove any dust.
From there, start spraying solvent in small areas, working from high to low. Be sure to use gloves, because the solvents can be harsh on sensitive skin. Spray the solvent, keeping it away from the windings in your alternator, and agitate it with some kind of brush. These brushes from Chemical Guys are great, but there are less expensive alternatives available at any auto parts store.
Rinse each area as you go, before moving along to the next section. You can use water from a hose, or you can have a spray bottle filled with clean water. We go through a lot of heavy-duty paper towels available at auto parts stores. The big boxes are the best value. You can also buy large selections of microfiber towels and wash them when you’re finished.
Once you’ve worked your way around the engine, hoses, radiator supports, and inner fenders, and are satisfied with how clean the engine bay is, you’ll want to dry the engine. Standing water can cause steel to rust, but it can also cause surface corrosion on aluminum parts and you want to dry those parts before that happens. Most people will tend to use a shop vac on reverse, but we’ve seen people using compact leaf blowers to blow the water off the engine, too., Whatever you do, just be sure that you’re not blowing contaminants back onto the engine.
In extreme cases, you may want to invest in a compact steamer to help remove dirt and grime. McCullouch now offers a steamer the size of a small vacuum with a set of attachments that allow you to carefully direct steam to particularly dirty areas without blasting the entire engine. For $150, it’s a steep investment, but if you’re passionate about keeping your underhood clean, it’s a terrific tool.
Repainting Worn Areas
There are areas under your hood that might need to be repainted in order to look their best. This isn’t typically something that needs to be done on a modern vehicle, but if you’re driving something older, paint may have flaked off of your valve covers, inner fenders, or other components.
Check your auto parts store to find the correct color of underhood paint. For black components, we always have a couple of cans of VHT’s Epoxy Black at the ready. It covers well, and it dries to a satin finish. Not too shiny, not too flat. Your local auto parts store likely has a whole section of VHT (an acronym for “Very High Temperature”) paints that will match just about anything you’re trying to accomplish under the hood.
Applying Protectant After Cleaning
Some kind of protectant spray is a good idea after you’ve detailed your engine. Most of these dressings have a UV component that protects rubber parts from sunlight, though there’s not a lot of sunlight under the hood. But if you use a product like this regularly, you can get away with simply spraying the engine down and wiping off occasionally, rather than a deep detail every time.
The type of dressing you use is sort of an aesthetic choice. We’re not a fan of the bright shine look, but others are. The Black on Black dressing from Chemical Guys isn’t obnoxiously shiny, and helps to bring black components that may have faded to a gray color back to their original rich black.
Once you’ve given your engine bay a good detail, it’s a lot easier to stay on top of it with some kind of regularity. You don’t have to detail the engine bay every time you hose your car off, but if you can get at it once a month or so, you’ll keep the engine looking fresh and new. And when it’s time to sell your vehicle, you won’t be making any excuses when the potential next owner comes to take a look at it. A clean engine bay – along with a well-detailed car – can make staying firm on your price a lot easier.
Craig Fitzgerald began his automotive writing career in 1996, at AutoSite.com, one of the first online resources for car buyers. Over the years, he’s written for the Boston Globe, Forbes, and Hagerty. For seven years, he was the editor at Hemmings Sports & Exotic Car, and today, he’s the automotive editor at Drive magazine. He’s dad to a son and daughter, and plays rude guitar in a garage band in Worcester, Massachusetts.
