Project Car Diaries: My Engine-Cleaning Techniques for Sensitive Old Cars

Engine bay cleaning has always been one of my favorite sidequests of the car hobby. I simply like looking at engines, for one thing, and it makes me feel like I’m getting to know my car without doing any work that’s actually challenging or mentally taxing. The transformation from dirty to clean under the hood is also particularly satisfying—even a maintained engine with more than 200,000 miles on it tends to sweat a little and getting the grime off always feels good. 

Undercarriage cleaning is a lot less fun and usually results in something gross falling into my eyes or mouth. Alas. But I digress. 

Taking the time to take a close look at the often-unseen areas of your car becomes increasingly important as a vehicle ages. This is especially true if you’re talking about a truck that goes through muck or a car that’s done rallycross (now that was a cleanup—never again). Dirt and road grime can hide leaks, or at least make it very tough to tell what their source is. A filthy engine also holds onto more heat, which can increase wear speed … fractionally, probably, but still.

Ideally, you should be paying pretty close attention to all fluid levels and potential leaks on any rolling restoration or project car that’s driven. I probably do a light engine cleaning on all my cars about six times a year, and the Montero in particular gets two big ones, at the beginning of winter and then again once the snow’s gone away for good.

I know some people will simply douse their engine in degreaser, and I’ve even seen plenty of folks cover electronics with plastic and powerwash under the hood. But I don’t trust myself not to hit something vital. And with an old car especially, attacking sensitive components with high-pressure water is a dice roll I’d rather not take.

The optimal solution for me, as an engine-cleaning savorer and careful workman, is a combination of rags, shop towels, sacrificial cheap microfiber cloths, cotton swaps, and WD-40 Specialist Degreaser & Cleaner EZ-Pods.

An alternative to pre-mixed heavy-duty cleaners, the Degreaser & Cleaner EZ-Pods are small but mighty pods you can carry for degreasing on the go. Drop a pod into a bucket or spray bottle and watch these tiny champions dissolve in minutes. Figuring out a ratio is simple—the baseline is one pod per 32 ounces of water (that’s a standard spray bottle size) and you can add more water to tweak the ratio to your liking. For extra degreasing and cleaning power—drop two pods!

There are plenty of quality degreasers out there. I’ve had good luck with some of the classic spray bottle options and wipe-style products as well. But since we started working with WD-40 Brand last year, the EZ-Pods have remained one of my favorite dirty-engine cleaning tools for two main reasons: versatility and price. 

You do buy your own spray bottle or applicator (they can be as cheap as $4). But then a five-pack of EZ-Pods retails for $12.98 and ships free with Amazon Prime—all you have to do once you get it is drop a pod in water, and that works out to less than $3.00 for a 32-ounce bottle’s worth of degreaser. If you spring for a 20-pack, your price per bottle is only about $1.65. 

Another advantage of the pod format is how you can apply it. The spray-bottle method is good for hitting medium-sized areas—engine covers, intake manifolds, intake tubing, the airbox—I give all that stuff a spritz before carefully wiping with a microfiber cloth I don’t mind ruining, or a blue disposable shop towel. 

For tiny spots, or anywhere I want to be super careful about where any spray gets, I like to pour a wee dram of my water/EZ-Pods mixture into a cup and then dip a microfiber cloth into it, and rub the surface I’m fixated on. 

If you’re paranoid about overspray or just have to get into a super-tiny crevice, you can use a cotton swap (aka Q-Tip), a toothbrush, or even a tiny paintbrush. I have found that the cotton swap works best, picking up dirt better than those alternatives I mentioned, but your mileage may vary. Regardless, dip something like that into your degreaser mixture, and you’ve got yourself an ultra-fine powerful cleaning brush. This is great for those weird little divets in an airbox, or areas near belts that you might be nervous about getting any kind of chemical on.

Finally, if you want to go the other way and hit a broad area, you can get yourself something like a pump sprayer jug that’s typically used for applying pesticides to plants. I got this one at Home Depot for about $12 but if you’re willing to shell out a little more, you can get battery-powered ones you don’t have to pump.

When you need to hit a larger area, like big tracts of vehicle frame or an oil pan and everything around it, just drop your EZ-Pods into water, dump it into the pump sprayer, and you’ve got yourself a degreaser shotgun. 

I like to work my way “down and in” with all this stuff. I pop open the hood, do a first pass with a shop vac, then do the big sprays on the engine, agitate and wipe, then zoom in on the tight areas, agitate and wipe, and finally move to the underside. I never bother to cover belts or wiring—I just spritz carefully and use one of my precision degreaser application tricks. Honestly, I usually end up doing the undercarriage the next day because I’m too bored and tired of cleaning to do a good job after the engine’s done. 

Move through quadrants, take your time, and enjoy it. Inspect every hose and piece of plastic for fatigue and cracks that might leave you stranded later. 

With any degreaser, you’ve got to be cautious of surface compatibility. Aluminum intake manifolds in particular, polycarbonates, and other fragile plastics, can be stained by some cleaning products. WD-40 Brand explains that EZ-Pods are “safe to use on sensitive surfaces like plastics, rubber, neoprene, stainless steel, carbon fiber, copper, aluminum, chrome, and painted areas,” which just about covers everything you’d find under the hood of a car.

But I’d still recommend starting very slowly, both with your concentration level of clear and your application of elbow grease. Let the degreaser do the work—agitate gently, and start with small areas that are harder to see.

It’s also worth mentioning that degreasing an undercarriage is a bit fraught. Oil and grease are effectively rust-preventative, acting as a barrier between the metal it’s on and the moisture in the atmosphere. Remove the grease and your metal is exposed. Once your vehicle's underside is dry, it might be worth hitting it with a rust inhibitor—there are so many options, that’ll have to be a whole other post. You could even spray your frame with some WD-40 Specialist Corrosion Inhibitor for protection. 

Once my engine bay cleanup is complete, the only thing left to do is decide whether or not I can bear to let it get dirty again. This typically results in my Montero resting in minty-clean glory until the next time I need to move something that doesn’t fit in my Civic. This year, I don’t know, Monty’s either getting a full-season slumber … or getting sent to Colorado for some cold-weather wheeling. If it’s the latter, you can look forward to at least one more good diary entry with this truck soon.