In-depth reviews Our take on each cleaner
We weighed every product against the same five criteria — cleaning power, surface safety, ease of use, value, and availability — with dilutions and safety claims verified against each brand's own pages. Here's how each earns its trigger.
1 
Meguiar's Super Degreaser D108
Best Overall
D108 is what the detailing trade means when it says 'degreaser': a professional-line concentrate from Meguiar's Detailer series that cuts engine grime fast and rinses residue-free, with an unexpectedly pleasant herbal scent doing the work sulfurous industrial products usually announce themselves with. The official dilutions tell the economy story — 4:1 water-to-product for heavy engine-bay and wheel-well duty, 10:1 for light and medium work — so the $29.99 gallon mixes into five-plus gallons of strong cleaner.
The workflow is standard degreaser discipline: spray onto a cool engine, agitate the grimy corners with a detail brush, and rinse before it dries — never on hot panels. Meguiar's positions it for exterior use, so keep it out of the cabin. It's a concentrate through and through: there's no ready-to-use trigger SKU, so budget a mixing bottle and thirty seconds of measuring.
One buying quirk our research confirmed: Meguiar's own store can't ship the gallon by standard parcel due to shipping restrictions, which is why most enthusiasts buy D108 from Detailed Image, Autogeek, or Car Supplies Warehouse. Minor friction, easily routed around — and on the other side of it is the best power-per-dollar in the category.
Check Price: Meguiar's Super Degreaser D108 →
2 
Simple Green Pro HD
Best Metal-Safe
The single most useful fact in this category: the two Simple Greens are not the same product. The original green All-Purpose Cleaner's own FAQ admits its alkalinity 'can accelerate the corrosion process' on unprotected aluminum — contact should stay brief and never exceed ten minutes. Pro HD, the purple heavy-duty formula, exists precisely to fix that: officially optimized for metals, safe on aluminum, stainless, and chrome, non-degrading to plastics, and clean-rinsing. An engine bay is a box of aluminum castings; buy the purple one.
The backstory checks out in outline: after the original's aluminum issue surfaced, Simple Green developed Extreme Simple Green Aircraft & Precision Cleaner for the aviation market, and Pro HD is its retail-market counterpart — enthusiast lore describes the two as closely related chemistry, and Simple Green's own FAQ names both as its aluminum-safe recommendations. Whatever the exact family tree, the retail result is a genuinely metal-respectful degreaser at hardware-store prices.
Official use rules are worth following: dilute 1:3 for heavy grime, 1:5 medium, 1:10 light — and no further; keep it under 109°F, don't let it dry on the surface, and spot-test first. At roughly sixteen dollars a gallon from any Walmart or Home Depot, it's the most accessible serious degreaser on this page, and the safest default for anyone nervous about what's under their hood.
Check Price: Simple Green Pro HD →
3 
Griot's Garage Engine Cleaner
Best Ready-to-Use
Griot's Engine Cleaner — that's the exact current name, plain and accurate — is the category's friendliest on-ramp: a ready-to-use trigger spray you point at grime with no dilution charts, no mixing bottles, and no guessing. Spray, agitate with a detail brush, and the grease, oil, and road film release for a rinse or wipe. At $11.99 for the 22-ounce (or $34.99 the gallon), it's priced like the convenience product it is.
It's designed as step one of Griot's two-product engine routine: clean with this, then finish with the separate Engine Bay Dressing, a water-based satin dressing that revives plastics and hoses. Keep the two SKUs straight — the shine and protection claims belong to the dressing, not the cleaner — and the pair delivers the full engine-detail result the how-to videos promise.
Griot's publishes refreshingly little chemistry marketing here — no dilution ratios (it's RTU), no surface-compatibility boasts — so our praise stays equally modest: it cleans typical engine bays well, gently, and conveniently, it's stocked well beyond Griot's own site (AutoZone, FCP Euro, Amazon), and the famous guarantee backs the experiment. Caked-on decades of grease want a stronger concentrate above; everything newer wants exactly this.
Check Price: Griot's Garage Engine Cleaner →
4 
SuperClean Cleaner-Degreaser
Best Heavy-Duty Value
SuperClean is the degreaser aisle's blunt instrument: the purple jug — the former Castrol Super Clean, sold off in the mid-2000s and carrying on under SuperClean Brands with the same positioning — whose strongly alkaline, sodium-hydroxide-based chemistry dissolves grease that citrus and APC products just annoy. Used full strength on a neglected engine's caked corners, it does in one pass what gentler bottles need three for, and the gallon costs around thirteen dollars.
Power at this pH demands respect, and the respect is printed on the label: gloves and eye protection are warranted, and the aluminum warning is real — 'avoid prolonged contact with aluminum and painted surfaces' is SuperClean's own language, not detail-forum caution. The honest engine-bay protocol: dilute per the jug's chart for anything but the worst grime, keep contact brief, never let it dry, and rinse thoroughly — especially near polished or bare aluminum, which high-pH cleaners can stain or etch.
One identity note from our check: SuperClean and Purple Power are different companies and different formulas, whatever their shared shelf color suggests — this review covers SuperClean only. As the heavy-duty half of a two-degreaser garage (something gentle for maintenance, this for archaeology), it's unbeatable money. As an every-wash engine mist, it's more chemistry than the job calls for.
Check Price: SuperClean Cleaner-Degreaser →
5 
Adam's Eco All Purpose Cleaner
Best Eco Pick
First, a catalog correction our research surfaced: Adam's sells no standalone 'Engine Cleaner' — the brand's official answer for engine bays is its all-purpose cleaners, led by this Eco APC built on EPA Safer Choice ingredients with a 'Direct Release to the Environment' formula. Since engine cleaning is the one detailing job where everything you spray runs straight off the driveway, the eco positioning here is function, not virtue signaling.
Adam's documents the exact engine protocol: engine cool, full strength on real grime or diluted 5:1 for lightly soiled bays, agitate with brushes, rinse thoroughly — safe on the firewall, plastics, hoses, and painted surfaces. For heavier filth the brand's separate heavy-duty All Purpose Cleaner steps in (with its own caveat: not recommended on delicate polished aluminum). Charmingly, Adam's own engine-cleaning tutorial also drafts its Tire & Rubber Cleaner and finishes plastics with Interior Detailer — the ecosystem answer, not a single hero SKU.
The trade-offs are the expected ones: pure cutting power trails the alkaline monsters above, the per-ounce price runs boutique ($23.99 for 32 ounces, gallons better), and stock on adamspolishes.com fluctuates — some sizes showed waitlisted at our check. For the weekly-washed enthusiast car whose bay needs freshening rather than excavation — and whose owner minds what flows into the storm drain — it's the right bottle.
Check Price: Adam's Eco All Purpose Cleaner →
6 
GUNK Original Engine Degreaser
The Classic
EB1 is the orange-and-black can that defined this category: GUNK's original petroleum-solvent engine degreaser — billed as their number-one-selling formula, 'specially formulated for older, greasy engines' — from the brand family (Liquid Wrench, Motor Medic) that Radiator Specialty Company has run since acquiring GUNK in 1976. Veterans knew this line as 'Engine Brite,' a name that still lingers in some retailer listings; the official name has dropped it.
The method is the same as it's been for decades: spray onto the grime, wait ten to fifteen minutes per the official directions, hose off. Solvent chemistry is why it works on the oil-varnished engines that defeat water-based cleaners — and why it deserves care: this is not an eco-formula, so mind the runoff, and Californians should look for the compliant low-VOC EB1CA variant, since the standard can isn't sold there.
One clarification that sorts out decades of shelf confusion: the foaming GUNK is a different product — Foamy Engine Cleaner (FEB1), the cling-foam formula marketed as safer on plastics, rubber, and paint. Choose deliberately: EB1 for old iron wearing real grease, FEB1 or a gentler water-based option above for modern plastic-covered bays. On its home turf — a $6 can versus a filthy old engine — the classic still wins.
Check Price: GUNK Original Engine Degreaser →
7 
Chemical Guys Orange Degreaser
Best Citrus
Signature Series Orange Degreaser is Chemical Guys' citrus answer to the engine bay: potent orange extracts and surfactants strong enough to run full-strength on the worst grime, with an official dilution ladder — 6:1 water-to-product for extreme cleaning, 10–15:1 for medium, 25–40:1 for light duty — that stretches the gallon across engines, undercarriages, tools, and tires. Application is standard: spray, dwell a minute or two, agitate if needed, rinse thoroughly, never on hot surfaces.
An honesty note the orange scent invites: citrus-scented is not chemical-free. The product carries a California Prop 65 disclosure, so treat it with the same gloves-and-rinse respect as everything else on this page — it earns its 'degreaser' title through actual chemistry, which is the point of buying it over an all-purpose cleaner.
The ranking friction is retail, not performance: at our September check both sizes showed sold out on chemicalguys.com, street prices swing constantly with CG's coupon cycles (the $49.99 gallon routinely sells in the thirties at Amazon and Walmart), so verify stock and never pay list. Caught in stock at a promo price, it's a pleasant, versatile middle path between the gentle RTU sprays and the caustic heavyweights.
Check Price: Chemical Guys Orange Degreaser →