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Weekend Workshop: how to repair your bent cooler

1 January 2016

Welcome to the Weekend Workshop — a place where you can save some cash by getting your hands dirty. These tech guides aim to arm you with the necessary information and knowledge to get out there and give it a go yourself, no professionals needed, and at a price that won’t break the bank. 

This time around we take an old beaten-up cooler and give it a new lease on life. This will work for intercoolers, oil coolers, radiators, diff coolers, gearbox coolers, and any other cooler you might have on your car. Not only are bent fins an eyesore, they also block air flow and reduce your intercooler’s capacity to transfer heat. Getting it looking like new again is not rocket science, in fact it’s downright easy, and this is possibly the cheapest workshop we will ever run.

Tools you will need

A quick search on Google will reveal you can actually purchase combs on the internet that are designed to straighten fins, but they are not of any use if you’re rocking an aftermarket cooler that has zigzag-pattern fins, as they often don’t fit the profile you’re trying to replicate.

  • A pair of flat-bottom tweezers
  • Two flathead screwdrivers
  • Small punch
  • Pick
  • Two blocks to sit the cooler on 
  • Hose
  • Soft bristle brush
  • Soft hammer
  • Steel bar 
  • Selection of punches

Step one:

First up, it’s a good idea to clean the cooler both inside and out to get an idea of the extent of the required rebuild. It’s very likely the inside of the cooler is swimming in oil thanks to a little blow-by in the turbo. To remove this simply block one end and dump a little petrol in there, swish it around and pour out the contents. Do this a few times, and you will see the petrol that’s removed gets closer and closer to clean petrol. You don’t need to put tons in there by any means. 
To dispose of this you should add it to your waste oil so it’s properly refined. For the exterior use a degreaser, a soft brush and a hose. Don’t rub the core, as it will only make matters worse.

Step two: 

If the cooler is bent or twisted, carry out step four before steps two and three. If the core is straight, begin step two. The first stage in straightening the fins is to steal the tweezers from the bathroom. You don’t want pointy-end types, but rather the flat-based ones. If the fins are really badly crushed use a pick or, like us, a fine punch with a sharp tip to get the fin to a point where you can get the tweezers on and straighten each fin. The aim of the game is to get the fins looking like new, so following the same lines. Make sure you are gentle, and don’t tear the fins out. An alternative to the tweezers is two flathead screwdrivers. 

Step three:

You will notice that once you get the fins all straight, the ends are more square than round, like the rest of the core. This is the final stage of the moulding. Take something round that’s about the same size as the original curve (we used a punch, but a toothpick, bolt or any other round object could work) and use it as a shaping tool where needed. It’s a tedious task, but the end result is well worth it, both aesthetically and performance-wise. Please note that the cooler will always be a little weaker in these places than before. 

Step four: what if it’s twisted and bent?

 If your cooler is twisted, place it into a vice using alloy plates, and do not tighten too much. Grab the opposite tank and slowly twist back into shape. If you can’t quite get enough force to twist it, take two pieces of wood (ours were about a metre long) and using two clamps, clamp to each side of the tank, then with a friend, twist back into place. If the tanks are not parallel, take a soft hammer and gently hit the top tank until the two tanks are parallel. Don’t hit it too hard, as you don’t want to damage the tank or end up tearing the core. Take your time. 
If the cooler fins are bent, you can beat them back straight using a soft rubber mallet and steel bar along the outside edge. Place the cooler upright on your bench, and work the mallet back and forth along the lower lip, which will pull it all straight. Work up and down both sides of the core. You might need to use a few different bars. It’s amazing how good you can actually get a really twisted and bent cooler. 

This article was originally published in NZ Performance Car Issue No. 227. You can pick up a print copy or a digital copy of the magazine below: