Structural damage: what to look for, and when to walk

Every other check in a pre-purchase examination is about money. This one is about whether the car will protect you. A modern body is engineered to absorb a crash in a designed sequence, and once that structure has been deformed and straightened without being measured, nobody can tell you how it will behave next time.

How a modern body is built

Almost all passenger cars now use a unibody, where the shell itself carries the loads rather than sitting on a separate ladder frame. Some larger off-road vehicles and pickups still use a frame, and the distinction changes what damage means.

In a unibody, the shell is designed as a system. Front and rear crumple zones are meant to fold in a controlled way and absorb energy. The passenger cell around you is meant not to fold at all. High strength steels are placed deliberately, and a repair that heats or replaces those areas incorrectly changes how the whole assembly behaves. That is the reason a straightened car can look perfect and still be wrong.

What you can check yourself

You do not need equipment for the first pass, only patience and somewhere with decent light.

• Seams and spot welds. Open the bonnet and the boot and look along the inner edges. Factory spot welds are evenly spaced and identical. Repair welds are usually irregular, ground flat, or replaced by a continuous seam.
• Seam sealant. Factory sealant is applied by machine in a consistent bead. Hand-brushed sealant in a channel that should be neat is a repair marker, and it is one of the easiest things to spot once you know.
• Inner wings and strut towers. Look for kinked or wrinkled metal, and for bolt heads that have been marked by a spanner where nothing should ever have been unbolted.
• Cracked paint along a fold. Paint chips from stones. Paint that has cracked in a line follows metal that moved.
• Panel gaps and door operation. Gaps that taper along their length, or a door that needs lifting to latch, point at an opening that is no longer square.
• Boot floor and spare wheel well. The most common place to find evidence of a rear impact that was tidied up.
• Sit inside and look along the sills. Ripples under the door seals are hard to hide and easy to see once you look deliberately.

What a professional examination adds

The decisive checks are measurements rather than opinions. A thorough pre-purchase examination puts the car on a lift and looks at the underside as a whole, compares diagonal measurements between reference points against the manufacturer's figures, checks suspension geometry to see whether alignment can be set and held, and reads paint thickness across every panel to find where filler sits. Any one of those can be explained away. Together they either confirm a straight car or they do not.

Ask for the measured figures, not a verdict. A report that says the car is straight is worth less than one that shows what was measured and against what reference.

Reading paint thickness into this

Paint readings are the usual route to a structural question. One panel reading high is a local repair. Several adjacent panels reading high together means the damage crossed panel boundaries, and damage that crosses boundaries usually reached something behind them. That is the moment to stop treating it as a cosmetic finding.

The reverse holds too, and buyers forget it: a car with even readings everywhere and no weld or sealant anomalies is very unlikely to have structural history, which is a genuinely reassuring result rather than merely an absence of bad news. Paint thickness readings covers how to build that map.

How findings get graded

Examination reports usually sort findings by severity, and the labels are worth translating into decisions:

• Informational. Normal for age and use. Not a negotiating point.
• Minor. Cosmetic or a wear item. Add up the cost and use it on price.
• Major. Needs work before or soon after purchase. Get a quote before agreeing anything.
• Critical. Affects safety or structure. Treat this as a stop rather than a discount, unless you have documentation and measurements showing the repair was done properly.

What records can and cannot settle

An insurance damage record confirms claims, so it can establish that an impact happened and cannot establish that one did not. A workshop record of a structural repair is genuinely valuable, and where the shop documented the job that record is signed by the shop that issued it, so a shared snapshot can be checked to confirm it has not been altered since it was generated.

The limit is worth stating directly. If a car was straightened in a yard with nothing written down, no record exists anywhere and no product can recover it. In this category the physical measurements are the evidence, and paperwork is corroboration. The full pre-purchase sequence places this last, because it is the check that can end a purchase rather than reprice one.