How to Install a Classic Mini Oil Cooler

An oil cooler has traditionally been considered a high performance modification for a Mini, primarily because of its standard fitment on the Mini Cooper S from early 1966, plus of course the BMC Works competition cars.

Testament to this was that an oil cooler was fitted to the RSP Mini Cooper introduced in 1990; somehow this authenticated the RSP as a ‘proper’ Cooper.

Fitting an oil cooler to sub Cooper S Minis was popular in the '60s and '70s when many used their Mini for everyday transport and some competition work at the weekend. It was also because of the Cooper S association, a bit like twin tanks, and many a lightly-modded Mini sported an oil cooler with the radiator grille omitted to show the cooler off to the max. 

So should you fit one today? It is not as essential as in the '60s, due to the huge advances that have been made in engine oil quality and performance, but if the engine is worked hard then you may still find this beneficial. This is especially true for trackday and competition use, or in warmer climates.

On cars used purely for road driving in the UK, an oil thermostat plumbed into the hose from the filter housing may be sensible, or a cover placed in front of the cooler itself to restrict airflow on colder days.

As a rough guide you should start to think about fitting an oil cooler at circa 90-95bhp engine output, but this will vary either way depending upon the intended use of the Mini. 

Fitting an oil cooler is not especially difficult - the mechanical side of it is actually very simple. It is the modification of the front panel that is the tricky part ,as it involves reshaping a rather reluctant part of the front panel. It is definitely easier with the engine out of the car, although it can be done engine in situ.

Below, we have reshaped the front panel as per Cooper S. It is also possible to cut the front panel lip at either end of the cooler ‘platform’ and this will make reshaping easier. Brackets could also be made up and fitted to support the cooler rad.

The oil cooler kit comprises of the 13-row cooler radiator and two braided stainless steel connecting hoses. In addition to the items in the kit, a Cooper S front panel stiffener plus a welder, rivets or screws, and a couple of suitably sized nuts and bolts for the cooler are required.

For full competition engines, look instead at the MED Setrab oil cooler kit, which offers a complete filter head upgrade, larger bore hoses and a premium cooler.

1) First off, the radiator grille and the front bumper will need to be removed from the car. It is worth marking the position of the grille on the front panel from the inside before removal – see picture 17 below.

2) The S stiffener fits to the front panel to the side of the original upright component.

3) The exact measurements of the modifications needed to the front panel. The measurements are approximate for the diagonal stiffener.

4) The front panel marked up with the locations needed. It is possible to make cuts in the rising lip of the front panel where the bending starts at either end and this would simplify the job, although would be less original in appearance.

5) The stiffener is fairly straightforward to remove. The lower end can simply be cut through with a junior hacksaw. Care is needed to avoid cutting into the front panel.

6) With the bottom cut free, the upper end can sometimes be bent to and fro, to break the spot welds. This one came away very easily. If it does not, the top can be cut too. Just be careful of leaving any bare metal exposed, as the Mini front panel is particularly susceptible to corrosion.

7) The stiffener coming away from the front panel. Care is needed as the edges will probably be sharp and need to be smoothed with a file.

8) The lip on the front panel now needs to be bent over inwards to create a flat mounting area for the oil cooler radiator. It is best done when the engine is removed from the car but it can be done successfully with the engine in situ and it was here! It is just a case of gradually bending down the required area using pliers or better still Mole grips or sheet metal welding clamps.

9) A panel beating hammer and suitable dolly can also be used although there is not a lot of swinging room for the hammer.

10) We found that modifying the offside area (RHD) of the panel was much easier with the starter motor removed…

11) …there is then much more room for the mole grips or hammer and dolly or both.

12) Once the metal is sufficiently and evenly bent over the area can be filed to show the high spots and generally tidy things up.

13) The cooler can then be placed in position to check that the platform is level and of correct width. The holes to mount the cooler can then be drilled ensuring that the cooler is located at least ¼ inch forward of the starter motor. Only the foremost mounting holes on the cooler are used.

14) If all is in order it is time to offer up the stiffener and drill fixing holes if required. On a different Mini, here we have used self tappers on the inside upper lip of the front panel, this method will be difficult when the engine is fitted.

The top holes need careful positioning and drilling, the lower end is easier as the stiffener can be held on the outside of the front panel and used as a template. If the stiffener is to be welded the metal will need to be prepared and paint stripped ready.

15) The stiffener then needs to be painted. Mark 1 and some Mark 2 stiffeners were finished in black, most Mark 2 and all Mark 3 in body colour.

16) An alternative top fixing method using self tappers is to locate the screws at the top.

17) The stiffener painted and in position. We did this as a final check for fit before removing it again ready to paint the front panel. The holes for the cooler have been marked drilled here using the grill location line for reassurance as mentioned in caption 1.

18) We filled any minor imperfections on the front panel; thick filler here is not a good idea, then primed the area, and painted it in two coats of body colour.

19) The paint was left overnight to harden and then compounded with T Cut; the result was a very acceptable finish and an excellent paint match.

20) The cooler radiator bolted in position.

21) All that then remains is to fit the two cooler hoses, lightly greasing the threads on the connections to ensure that everything will come undone again if needed in the future. These are standard type rubber hoses; in our latest kit these are upgraded with a stainless steel overbraid.

22) The original metal filter to block oil pipe must be removed and the long hose connects to the filter head

23) ….and the short one to the engine block. You can’t get this wrong as the connections are different. The engine should then be run to check for any leaks, after which the grille and bumper can be refitted. Demonstrated on an engine out of the Mini for clarity.