Gearbox heating

There has been a lot of talk on the Australian Iveco chatrooms/forums about transfer gearbox overheating and failures.  Some of the Australian users have installed oil cooling systems to their transfer gearboxes (see Don’s website for more details:- http://www.goingbush.com/iveco4.html ) But before we go down the route of installing a cooler for the transfer case, I want to gauge the issue by installing a gearbox temperature monitor.  I am hoping that by having the 100 kph speed limiter, and by routinely driving at only around 80 kph (mostly for fuel efficiency), I will not be over-heating the gearbox.

I looked for the specifications of the transfer gearbox but Iveco does not publish any information, specifications or limitations. However the SCAM website does provide a data-sheet for the 24 speed transfer gearbox.  SCAM highlights two limiting factors for the inlet shaft:

1. A high-range maximum of 4000 rpm; and
2. A low-range maximum of 1500 rpm.

With Cuthbert’s Michelin XZL 255/100 R 16 tyres, the above rpm limits equate to a maximum theoretical speed of 138kph in high-range, and of 111kph with the half-gear selected.  Both of these are well above the limit of Cuthbert’s XZL tyres (and the speed limiter) of 100 kph.  However with low-range selected, the maximum speed drops to just 16.6 kph, and with the half gear selected, a mere 13.4 kph!  Obviously these low-range maximum speeds are very easy to exceed.

When driving, I have found that 3rd gear in low-range, is about the same as 1st gear in high-range with the half-gear.  I have been changing back up to high-range if I find myself reaching 3rd gear in low-range. Fortunately, this has been keeping me within the limits for my transfer gearbox.

Fitting a gearbox temperature monitor

Given all of the above research, I decided to try to keep an eye on the process and installed a transfer gearbox temperature monitor.  I chose the Engine Watchdog TM4. I had seen that Don (www.goingbush.com) had installed this model on his vehicle and it seemed to work well.  The TM4 can monitor two pieces of equipment simultaneously, so I have installed the gearbox temperature monitor in such a way that I can monitor and compare the temperatures of both the main gearbox and the transfer gearbox.  With this I should be able to see whether either of the gearboxes are overheating*.

(* – Note: As usual, there is nothing in the Iveco vehicle manual or the workshop manual specifying the maximum temperature limit. However, in the Body Builders’ manual, under the PTO section, it states that the maximum temperature for the gearboxes in continuous use is 110°C).

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