Just cool it, will ya?

The how and why of transmission heat management

It’s getting hard to buy a manual-shift 4WD. Even among the tougher new trucks, automatic transmissions are beginning to dominate.

They can be super reliable if looked after, or a huge pain in the backside financially ($10,000 to replace) and in terms of inconvenience if neglected. It makes sense to manage factors that affect the lifespan of a transmission.

Because a 4WD tests many components to extremes, it can be tricky to keep components working.

Enemy number one is heat. A transmission needs to run below 100 degrees C. The only way to deal with excess heat is to fit an aftermarket cooler.

The first question to answer, though, is whether to go DIY or take the job to the experts.

Adding cooling is relatively simple, but for the time-poor or those who fear drilling through the radiator (!) a local workshop might be safer.

The actual transmission coolers are not expensive at all, and many manufacturers offer kits for specific vehicles with all the hoses, clips and fittings needed. The important thing is to decide how to fit them, and where – in airflow through the grille, obviously

– but equally, out of harm’s way. Branches and bush can intrude and pull a line or even pierce the cooler matrix.

Mount the new cooler solidly. Most kits include mounting hardware, but if going fully DIY, it’s an idea to use exhaust system ‘cotton reel’ rubber mounts bolted to the cooler and to solid parts of the truck.

Watch out for hose length and avoid sharp angles – the latter are the enemy of good fluid flow; the former can affect fluid pressures going to and from the transmission.

Keep an eye on the air path. Best practice is to have unrestricted airflow in, and a good space behind so the air can get away from the cooler. It is simple enough to wrap the cooler in a shroud that makes sure air has greatest cooling effect and doesn’t spill past the unit.

All auto 4WDs already have a cooler included in the front end, often built into the water radiator matrix. The new cooler can take trans fluid coming from the transmission or be fitted in the return line. The latter is the most efficient in terms of cooling but it does mean the transmission will take longer to get to operating temperature; the other option lets the trans warm up more quickly but doesn’t provide ultimate cooling in extreme conditions because the fluid is passed back through a warm environment on its way back to the transmission.

There are two must-do requirements for best trans protection when fitting the new unit – also fit a new filter inline; and if at some point the transmission does need a rebuild due to a full-scale mechanical failure, it’s safest to biff the cooler/s. The units don’t take well to efforts to reverse flush them, and any broken bits of transmission can remain in the cooler until they get dislodged and end up in your fresh new transmission. A couple of hundred dollars spent on the new oil cooler and filter is a cheap insurance against further costs.

❝Best practice is to have unrestricted airflow❞

An auxiliary oil cooler will keep that auto transmission alive. Spot the mistakes here though. The trans cooler is mounted in front of the intercooler which is in turn mounted in front of the radiator. Summing up: 1. Air gets stalled and causes overheating. 2. New cooler mounted to the intercooler and not a bracket. 3. The fluid lines have sharp bends to go in and out of the cooler and the lines are very long. 4. Using zip ties to tidy up the oil lines creates rubbing points where the lines can chafe against each other and other components.