Cooling and all that Jazz

Nothing ruins driving your rod/kustom/yank more than constant worrying about overheating. With a little forethought this can be avoided. The science of cooling is complicated and made more so in engine swaps by space limitations. An insight into the basics of radiator operation and design will enable you to make a more enlightened decision on selection of basic rad and core.

The main type of rad for many years was the top to bottom flow type, made from copper with copper finning soldered to the tubes. Top and bottom tanks are made from brass, soldered to what is known as the tube plate. This is a pre-formed plate where the vertical tubes enter and are individually soldered to the plate. There are mainly two types of finning, one where the fins run horizontally across the radiator (gill on tube) and the other where the fins run in a zig zag pattern vertically between tubes (pac construction). The number of fins per inch affects cooling, as does the number of tubes in a row, and the number of rows in the rad.

The other style of rad is the crossflow where the tanks are on the sides with the water flowing horizontally rather than vertically. This style came about because of car design necessitating lower bonnet lines. A huge rise in the cost of copper and brass in the mid-seventies meant the development of alternative materials for cooling as in aluminium cores with plastic tanks. The need for lighter cars has meant this is now o.e.m. standard.

Modern production methods and cost cutting means that many replacement cores are only adequate for their design, i.e. an original 3 row GOT row as fitted to a MKII Zephyr will cool 350ci without a problem but it’s modern equivalent will only cool the original straight six. So if your current rad is doing its job and needs replacing, make sure that the same specification core is fitted not a modern replacement.

Now for some technical stuff. Firstly, air will always take the path of least resistance. So, if its not forced to go through the rad by ducting it will go around, with reduced cooling air to the rad. The worst car for this is obviously a T. Once you start fitting B style shells there is a form of ducting and of early rods the 34 probably has the best for of ram cooling. To enable a T style rad to cool the fin pitch needs to be very open or air will go straight round or not reach the rear most tubes.

The firm I worked for had many branches and one built a rad for a well-known Fad style motor, with a blown 427. They used a 6 row with 15 FPI and cooling was adequate but marginal. I built a rad for a 428 blown fad motor and used a 10 row with 6 FPI and, once bleeding problems were resolved, it would sit in heavy traffic all day.

I also built a rad for a blown big block (460 I think) in a Mustang. The car used a crossflow rad and the tank sizes restricted it to 3 rows only, but luckily my firm manufactured a 3 row which had the cooling capacity of a 4 row. The same engine transferred to a B shelled 27T then used a top to bottom flow MKII Consul rad, which was 25% shorter than the Mustang rad. Again the uprated 3 row was more than adequate for the job, but only once the ducting and fan shrouding was sorted

The MKII Jaguar rad used to be the staple choice for rods, but these are now in very short supply. Suitable, better looking alternatives, can be found in 100E, MKII Zephyrs and tractor rads. Many crossflow rads can be turned on end and then sealed around the grille shell. Just by turning the rad on end a cooling increase of 30% will result i.e. a Marina 1800 rad will cool 2600cc!! Likewise moving a rad mounted inside the wing on a transverse engine like Mini, 1300, Maxi etc., will cool double the amount when correctly mounted at the front of the car. I’ve often used a Mini rad in a 1600cc 100E, or a 1800 rad in a Y to cool a Rover V8!!

Even within the same range of cars there can be many variations. A Rover 3500 rad is thicker than a 2.6 and putting an air con unit in increases the rad from a 2 row to a 3 row (the heat from the air con is transferred into the rad, meaning it needs to cool better). An injection radiator is more efficient than a carb model and normally the same as a diesel variant.

However, do bear in mind that too many tubes in a rad will cause overheating!! Sounds strange but what happens is that the water travels through the radiator so fast that the heat is not transferred to the finning, and thence to the air. Over cooling normally occurs because too many fins per inch are fitted. To get an idea of what’s needed to cool your car look at what was fitted as standard. Measure the square area of the core and multiply by the number of rows. Now measure your proposed replacement and do the same maths. If it matches OK, if its smaller think again! Look under the bonnet of a stock Mustang and you will be surprised as the rads not that much different to an early Transit. A friend fitted a Bedford 330 TK rad to his Mustang and it overheated. Much against my better judgement and at his insistence I uprated it, and yes you guessed right, it got worse. Resorting to a towing duty diesel Transit rad resolved the problem.

Many rads are fitted with internal trans oil coolers. These are barely adequate and a great source of problems as many become porous and allow water into the gearbox totally destroying it. Always use an air to trans fluid separate cooler and don’t worry about sealing the trans cooler in the rad, unless they have ruptured water will not leak out.

The location of top and bottom pipes also affects cooling. The pipes should always be diagonally opposite to ensure use of the complete core capacity. When the pipes are directly above each other then the top tank needs a spreader plate incorporated into it to direct the water flow to the other end of the radiator. These pipes, and all tubes, etc., are soldered together, use of too much heat i.e. brazing will cause the rad to leak like a sieve and it’s a skilled job to repair. A local garage had a leaky pipe which would have cost £15 to repair. They decided to braze the pipe and the resultant mess cost £100 to put right!!

Hopefully this article has given you a better idea of how to select the correct rad in the first place. My follow up article will deal with dialing in your new rad and troubleshooting your overheating problems.

Kev Rooney.

Tech Section