Should you rustproof a car from Japan? What to know before the coat goes on

Search for this and most of the answers come from businesses that sell rustproofing, and they say yes. Whether your car needs it, and with what, is a question for a garage where you live. It depends on the car, the state of the metal and the roads you'll drive on. We don't rustproof cars and we don't recommend products.

What we can tell you is what a coat does to what can be seen underneath, from my own cars, and what to get on record before one goes on.

A coat hides the metal under it

I haven't had my Prius α coated. That's why the photos on underneath a car from Japan show its rust as it is: on a frame-like part behind the passenger door, it's the kind I'd call bad. On another car of mine, I had the underside rustproofed after I bought it.

Once a coat is on, what's under it is out of sight. A photo can't see through it, and neither can someone standing next to the car. A coat put on over rust hides it from the next person who looks, and if you're buying a car that's already been coated, that person is you.

Before anything goes on: a record of the metal

If you're buying a car in Japan and plan to have it treated once it's home, the photos taken in Japan may be the last clear look at the underside anyone gets.

1. Ask the dealer whether the underside has been coated, and when. A car can be coated by a previous owner at any time, so the listing may not say.
2. Ask for photos underneath, from the front and back, as far as can be seen without lifting the car. Our photos to ask a Japanese dealer for has the wording.
3. Keep the photos with the car's papers. If a garage later finds something under a coat, you'll know whether it was there before.

On an On-Site Vehicle Viewing, we photograph what can be seen from ground level, without lifting the car. Where a coat covers the metal, we photograph the coat and mark what's under it as Not verified.

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Don't cars from Japan arrive without rust?

Some do. Mine didn't: it's a Japanese-market car, first registered in Japan in 2012 and bought used here, and it has a lot of rust underneath. About half of Japan's land is officially a heavy snowfall area, so where in Japan a car was used matters more than the country. The figures, and the difference between rust on a part and rust in the body, are on rust on the body or a part.

If the car is going to New Zealand

New Zealand's border inspection looks underneath. NZTA's guidance says a car must be reported if signs of fresh repair, rust prevention, acid wash or under-sealing to any part of the vehicle structure are evident, and its technical bulletin on acid-washed imports says such a car must be referred to a specialist repair certifier. So a coat that's new on arrival is something the inspector is told to notice. The rest of the border process is on our New Zealand import guide.

What we can't tell you

• Whether your car should be rustproofed, or with what. That's for a garage where you live.
• What's under an existing coat. We mark it as Not verified.
• How long a coat lasts, or whether one was done well.
• Whether a car has been in a flood or had its underside acid-washed. We photograph what we can see. See repair history and flood cars.

Written by Yoshiaki Sagara, a paintless dent repair and detailing technician in Japan. He looks at cars for overseas buyers through Ninja Desk Japan. About us

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