Engine Paints

Preparing an engine for paint

Decide, record, strip, degrease, mask: the preparation that decides whether engine paint lasts one season or ten years.

Updated 2026-09-18

On this page
  1. Decide what goes where
  2. Record the original paint before you strip it
  3. Strip the old paint
  4. Degrease, then deal with the degreaser
  5. Mask
  6. Sources
  • Decide which paint goes on which part before anything comes off. Ratings differ inside a single range.
  • Photograph and note any original paint before you strip it. Once it's gone, so is the evidence.
  • An alkaline degreaser leaves a surface paint won't stick to. It has to be neutralised or rinsed right off.
  • Sanding makes the dangerous dust. Old paint may contain lead.
  • The block must be completely dry before the first coat.

Decide what goes where

Settle three things before you pick up a tool: which parts get painted, which stay bare or plated, and which product goes on each. The choice affects more than looks, because heat ratings vary inside a single product range.

Hycote's data sheet for its Engine Enamels gives 300°C for Aluminium and Matt Black and 140°C for Gloss Black. The two higher figures carry an asterisk: full solvent resistance only comes after a heat cure at 220°C for 90 minutes. Pick gloss black because it looks right on a rocker cover and you have picked a 140°C paint.

The makers are also specific about where each product belongs. Hycote's enamels are "primarily for use on engine blocks and cylinder heads". VHT lists blocks, starters, brackets, water pumps, valve covers and transmissions for its Engine Enamel, and keeps FlameProof for headers, exhaust manifolds, piston domes and the inside of heads.

So split the job on paper first. Block and head in engine enamel. Manifold and downpipe in a very high temperature coating. Anything that has to come apart again soon, left alone. Manifolds and exhausts have a process and a cure of their own.

Record the original paint before you strip it

Stripping destroys the evidence. Once the block is bare, the only record of what the factory sprayed is whatever you wrote down beforehand.

Look before any abrasive goes near it, and look where nothing has rubbed: under mounting brackets, behind the dynamo or alternator, on the rear face against the bellhousing, inside the timing cover. Photograph what you find in daylight with something of known colour in the frame. A grey card is ideal, and a sheet of white printer paper will do.

If a sound patch of original survives, it can be measured instead of described. How the reference is made sets out the protocol: a spectrophotometer reading taken on the surface and stored as Lab*, with the on-screen colour derived from that reading.

Then send us what you found. A dated photograph and a location on the engine are worth more than a forum recollection, and an unfaded original that can be measured is worth more than either. It ends up in the colour reference.

Strip the old paint

Every data sheet asks for the same starting point and gets there a different way.

VHT's Engine Enamel sheet says to remove loose paint, rust, dirt and grease, and that the surface "can be accomplished by sand blasting or sanding the surface with 320 grit sandpaper or equivalent". Its FlameProof sheet asks for more: scuff or sand until the bare metal is bright and shiny, and blast any aluminised or galvanised pipe.

Hycote asks for rust and loose material to come off with a wire brush or wet-and-dry paper. POR-15 treats two cases separately. Sound old paint is roughened with 320 grit or a scuff pad, with anything blistered or loose removed. Bare or rusted metal gets POR-15 Metal Prep, kept wet on the surface for 15 to 20 minutes and rinsed off, which leaves a zinc phosphate layer for the next coat to key into.

If you have the block blasted, the risk is where the media ends up. Grit lodged in an oilway or a water jacket will find a bearing sooner or later. Plug and tape every opening before it goes, and wash and blow through every gallery when it comes back, whatever the blaster tells you.

The health risk is in the sanding. HSE's guidance on dust in vehicle repair notes that lead was used in some older body preparation, and that powered discing and sanding can release high concentrations of fine dust that is a serious hazard. Its advice is tools with built-in extraction or a portable extractor, disposable overalls and an FFP2 mask where needed. Assume the paint on a sixty-year-old engine contains lead unless you know it doesn't.

Degrease, then deal with the degreaser

An engine is oily in ways a body panel never is, and the residue you can't see matters more than the grease you can.

POR-15's engine painting kit instructions explain the trap best. Its Cleaner Degreaser is mixed one part to three of hot water, or one to one for baked-on oil, sprayed on, brushed until the grease dissolves, and rinsed well. Then comes the line that matters. The degreaser is caustic and strongly alkaline, coatings stick badly to alkaline surfaces, and so the acidic Metal Prep step that follows "is very important". Wash a block with a strong alkaline cleaner and stop there, and you have made the surface worse than when you started.

VHT's route is a grease and wax remover before abrading and again afterwards, because sanding drags up contamination from the pores of the casting. Hycote asks for a detergent or emulsifiable solvent cleaner, a thorough rinse and dry, and a final wipe with brake cleaner, white spirit or thinners.

POR-15 then says what all of them mean: every part of the engine must be bone dry before the first coat. Cast iron holds water in its pores and in every blind hole. Compressed air and a warm afternoon do more than a rag.

On the solvents, HSE's advice for vehicle repair is to compare safety data sheets and choose the least harmful cleaner, use enclosed cleaning equipment, never clean parts in an open bucket of solvent, and wear suitable gloves and replace them often.

Mask

The makers' sheets say only to mask surrounding areas against overspray. What follows is ordinary engine-building practice.

Keep paint off anything that seals, locates or threads: gasket faces, machined mating surfaces, dowels and their holes, threaded holes, core plug seats. Plug every opening into the engine, including ports, oilways, the breather, the dipstick tube and the distributor hole. Old bolts run a few turns into the threaded holes are quicker than tape and keep the threads clean. A smear of grease on a machined face will stop overspray keying, provided you wipe it off before assembly and keep it well away from surfaces you do want painted.

Stamped engine numbers are a judgement call. Factories generally painted straight over them, and thin coats leave them readable. Riveted identification plates should be masked or removed.

Anything you plan to plate, polish or machine later should be out of the spray path altogether. Hycote's sheet says not to use its enamel on surfaces that will later be coated with something else, and cleaning enamel off a part you wanted bare takes longer than masking it would have.

Sources