Install NP 242 Transfer Case & 4L80e Transmission Temp Gauges

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Why do you need to know the oil temperature of the transfercase and the transmission? Under stressful conditions the oil temperature will rise to the point that the oil will break down and burn. The oil will loose it's lubricating properties and cause premature wear or destroy the unit. As you watch the gauges over time you will get a sense of what's normal. If something begins to go wrong it may show up in the temperature readings first.

Both the transfer case and the transmission use Dexron III oil. When new the oil is bright red. If it has been stressed (overheated) it will begin to darken, smell burnt and finally turn brown. I once drained a transfer case full of soupy brown sludge. Because transmissions have clutches you might see residue and pieces of clutch in the fluid. Dexron is rated for maximum life at 175° f. Another reason to keep the transfer case temp down is to preserve the plastic / nylon shifter parts in the case. If your case starts to shift hard the plastic pieces may be disintegrating.

Examples of potential stressful conditions are:
Driving over 70 mph
Ambient temperatures over 90°f
Climbing steep highway grades, especially mountain passes
Spinning your wheels while stuck
Transmission cooler full of mud

Example of what can go wrong:
Burning the oil in the transmission and transfercase can cause the following:
Loss of fluid causing loss of transmission pressure
Burn transmission clutches
Damage torque convertor
Torque convertor not locking up
Damage Transmission pump
Premature wear of all moving parts in transmission and transfercase
Stretching tcase chain

ATF Type Burning Point Flash Point Fire Point
Dexron IIE   160°c (320°f) 175°c(345°f)
Dexron III 260°f 185°c (365°f) 220°c (428°f)
Synthetic 300°f 236°c (460°f) 250°c (482°f)
These are approximate. Each brand differs

Temperatures owners are reporting:

Driving at sea level on flat roads in my 98 Turbo Diesel Wagon:

When I first installed the gauges (March 2003) I noticed that the transmission warms up first. In fact, this is a good way to know that you have the correct senders hooked up. On a day that was 50°f the trans warmed up to 150° after driving in city traffic for about 15 minutes. The transfercase temp was just moving the needle at 100°f. Once I got on the highway going 65 to 70 the trans came up to 160° and the tcase came up to 150°. Both temps were always about 10° apart. Once off the highway the trans and the tcase stayed at about 150°f.

Driving at sea level on flat roads in a 2000 Turbo Diesel Wagon (summer):

t-case is between 140° and 240°; I got it to 240° once while doing 80 mph in 90°+ temps. Driving at 70mph the t-case heated up to around 225°, the transmission was around 200°.

Tranny is between 120° and 240°; once in OD it went down to around 160° no matter the ambient temperature or load. Driving around 65-70 it will go to 230° after an hour or so. Driving at 75-80 for about 20 min. It will go to 250°-255°. This is the max I have seen it.