Gearbox/TC temp switch/wiring?

**AK83** · 13th January 2017, 10:50 PM

1998(actually '99, but 98's close enough!) Tdi Auto.

Little red gearbox temp icon lit up one day(and freaked me out a little).
I then worked out that either a switch has died, or the wiring has shorted.
Light is on all the time.

I've searched as far and wide as I could on the topic and it's most likely to be the auto temp or T/C sender?
I don't remember any temp sender unit on the T/C(recoed a few months back) tho.

I can't find the auto's temp sender unit thingy. I probably have, but didn't know it.

Wiring diagram indicates a black and light green wire which goes all the way to the T/C sender unit, and then splits to a purple and black wire for the auto temp sender.
Most wires seem to be all (greasy) black colour tho

All help WRT the senders and or wiring would be appreciated.

TIA.

**Rick1970** · 14th January 2017, 07:27 AM

auto temp sender should be tee'd into the cooler piping, down near the lower left hand side of the radiator from memory.

**AK83** · 14th January 2017, 09:49 AM

Originally Posted by Rick1970

.... down near the lower left hand side of the radiator from memory.

awesome! thanks.

**AK83** · 14th January 2017, 11:46 PM

Once again, thanks Rick.
Been under the car for the odd job(oil change etc) but never noticed it, mainly because the plastic cowl(splash cover) partially obscures the pipes to the cooler.

Pulled the connector off the switch, checked wires for shorting, all good, tested the switch for resistance, but couldn't be stuffed because of limited accessibility .. but!

with the connector not attached, turn ignition on, warning light on dash came on for 3 secs or so and then went out .. you beauty I thought!
Connected the plug back onto the switch again, did the same with the ignition and same thing happened .. ie. problem automagically solvered itself

So I'm thinking that the switch came on and got stuck and my tinkering unstuck it and now all good .. easy fix.

BUT! ... I noticed that the trans has it's own cooler, rather than like with V8's with the cooler in the radiator tank system.
Above the pipes is a plastic shroud/splash deflector thingy which shows massive signs of extreme heat burn marking from the pipes.
The pipes(not so much the cooler) have got so hot they've melted their shape into the plastic splash deflector 99% through the plastic.
Granted that plastic does look very flimsy and thin, but I'm now worried that the trans has overheated either recently in the past(maybe when the light first came on) .. or maybe (more likely) in the long past.

The burn marks do look a little old, not shiny and new.
When the light first came on, I did check the engine coolant, not realising that it was a trans icon(I really need to get glasses!).
I don't remember any unusual smell, especially any burned plastic smell which I'd have picked up immediately.

Trans was serviced about 10K klms ago now, comments made by 4wdIndustries kid that did the job were along the lines of: "fluid was very slightly darker than they like to see, but not bad. trans seems fine tho"

Checked fluid level now.
Level is fine, colour is a nice clear red, doesn't smell bitter/burned in any way.
Trans shifts fine, never any issues.

I don't tow, maybe a 6x4 once or twice a year if the need arises.
One of the previous owners did tow something large tho, they had stiffer and raised rear springs and an electric brake controller fitted(I removed due to surplus requirements).

Question is, how much heat can they take .. and I'm now thinking a temp gauge for it may be a good thing too.
Is the burned out splash deflector a common issue?

**gavinwibrow** · 15th January 2017, 03:06 PM

For what its worth a trans gauge is a good thing for towing or low speed/other hard work eg low range in them thar hills. There is at least 1 detailed thread on here plus Ashcroft have a section advising of max recommended temps, copied below - might be just for the ZF4HP22 and 24 auto D2, but good starting point.
I would not be without mine, but mainly for towing my brick.

Looks like the superscript degrees sign becomes a ? but is for both Fahrenheit and Celsius.

Automatic Transmissions

OIL TEMPERATURE MEASURED AT CONVERTER OUTLET TO COOLER:

300? F / 149? C
The maximum allowable temperature. This is the recommended place to install a temperature gauge or sensor. Do not allow the converter outlet temperature to exceed 300? F. The temperature at this location will vary significantly because of load, hill climbing, etceteras. If the temperature reaches 300? F, reduce throttle. To lower transmission temperature with transmission in neutral, run the engine at 1,200 RPM for at least 2 - 3 minutes while keeping a close check for signs of engine overheating. A transmission in a heavy throttle, stall condition (a typical situation is rocking a vehicle stuck in mud, sand, or snow), may increase temperature at a rate of 1? degree per second of stall.

OIL TEMPERATURE MEASURED AT OIL PAN OR SUMP:

150? F / 66? C

The minimum operating temperature. Note: It is possible in low ambient temperatures to overcool the transmission with auxiliary oil to air coolers. Oil to water coolers in standard factory radiators will normally not overcool a transmission.

175-200? F /
77 - 93? C

Normal pan oil temperature operating range.

275? F / 135? C

Maximum allowable oil pan temperature for short durations during long hill climbs.

300? F / 149? C

Damage occurs to internal transmission parts, including warpage of metal parts, degradation of clutches, and melting of seals. Transmission oil oxidizes, (forming varnish-like substances causing further clutch slippage and compounding heat build up) and transmission oil life is extremely short.

AUTOMATIC TRANSMISSION FLUID LIFE / TEMPERATURE RELATIONSHIP:

Automatic transmission oil can provide up to 100,000 miles of service before oxidation requires replacement, at an operating temperature of 175? F. Above this temperature, the oil oxidation rate doubles with each 20? degrees F increase in oil temperature. See chart.

DEGREES F / C

MILES / Km

DEGREES F / C

MILES / Km

175 / 79

100,000 / 162,500

295 / 146

1,500 / 2,438

195 / 90

50,000 / 81,250

315 / 157

750 / 1,219

215 / 102

25,000 / 40,625

335 / 168

325 / 536

235 / 113

12,500 / 20,313

355 / 179

160 / 260

255 / 124

6,250 / 10,156

375 / 191

80 / 130

275 / 135

3,125 / 5,078

395 / 202

40 / 65

Note: Transmission oil and filter should always be changed more frequently when driving with heavy loads (RVs), typically at least every 25,000 mile intervals, since converter outlet temperatures then normally far exceed the ideal 175? F.

Cheers Gavin

**AK83** · 15th January 2017, 04:00 PM

Thanks for that Gavin.(I should have checked it myself really .. didn't think too)

My service plan is going to be service the trans with every cam belt service.

I have no plans to tow heavy loads.
But the reason I got the Disco was to start doing desert trips once again(like I used to in my RRC years back).
More so than heavy going trails, but the odd slow trail every now and then is on the horizon.
So my target maximum trans temp would be something like 100 degrees C going by Ashcrofts values.
The previous owner of my D1 didn't even know how to put it in low range, or use the difflock, and he sometimes towed a very light tinnie to the local creeks and rivers.
It took the two of us to use a bit of force to move the difflock/high low selector on my test drive, but it finally moved.
It was one of the previous two owners that had the electric brake controller fitted and must have towed a heavy (something) around the place.
TC broke a bearing of some kind about a month after I bought it. A changeover TC was duly fitted. No idea on the history of the trans tho, which is why I had it serviced at the same time as the TC change.

And if Ashcroft suggest the normal pan operating temps(of 77-93C) then obviously the best location for any temp sender would be in the pan.

**gavinwibrow** · 16th January 2017, 01:37 PM

Again, for what it is worth, yes mine is in the rear of the pan. I have heard you can get a version that uses/attaches to a bolt, but I actually have a sensor in the oil. Got an extra bit welded onto the back of the pan so I could mount the sensor horizontally and more protected (at least while going forward) by the pan itself.
Attached pic is before I had the pan modified. Can't seem to find the after version at the moment.
cheers

**Old Farang** · 16th January 2017, 03:23 PM

I have a 1998 D1 auto that has just over 200K Kms on it. I do not tow anything but it is driven mostly in stop start slow traffic jams in Bangkok, in continuously hot conditions.

I am interested in what you regard as a "service" with these boxes? If just draining the oil and maybe cleaning or changing the filter is considered a "service", then I suggest that you are not achieving much. It is not possible to drain much more than around 60% of the fluid, even if removing the sump. The "filter" is more of a "screen", rather than a filter as in engine oil.

I have a Wynn's flush and change done on my gearbox every 25,000 Kms. I have never had the sump off so the filter / screen has never been changed. The full amount of ATF is changed with this type of service, and the old fluid always comes out discoloured, regardless of the fact that it is still showing a serviceable colour on the dip stick.

I do not have a temperature gauge, and the engine cooling system has to be kept in top condition, given that the transmission cooler heat is contributing to the load.

In the type of driving conditions encountered here, it is not always possible to change into neutral while stopped at traffic lights, but I do so if possible. It is interesting to note from Gavin's post that the fluid temperature will rapidly drop if the auto is placed into neutral for just a few minutes.

**gavinwibrow** · 16th January 2017, 11:14 PM

True/good point Farang, plus I think I forgot to mention that I also have a HD dedicated ATF cooler/radiator installed.
Happy hunting all.

**AK83** · 17th January 2017, 11:46 PM

Originally Posted by Old Farang

....

I do not have a temperature gauge, and the engine cooling system has to be kept in top condition, given that the transmission cooler heat is contributing to the load.

....

On my 99 model, I don't think heat will add all that much to the coolant temp load.
I thought the auto trans cooler was integrated into the side of the radiator tank(engine oil is), but it's a very low profile wide cooler, independent of the rest of the cooling system.

On the V8, it looks like it's integrated into the (passengers) side of the radiator tank.

I've removed the plastic shroud/splash deflector from it's place below the trans cooler. I kind'a had too, because it's in a few pieces and it woudl probably have fallen off anyhow.
so the gap between front grill and front of radiators, between the chassis rails is now all air.
I reckon a bit more air flow from underneath will come up and through too now.
Time will tell.

My D1 has a bull bar(ARB type) and I'm contemplating making up a small scoop thingy to pull more air up from under the bar into the radiators too.

My car sits on about 88c at a slow crawl/idle in hot conditions(35+), with the A/C on.
On a run(eg. 80+ k/h) is when it starts to rise, and seems to top out at about 94-95-ish .. give or take.
So with vehicle on the run and A/C on, it heats up(opposite to what you'd expect!)
Without A/C on, the car sits between 83-85c irrespective of how the car is driven. Hard up hill(EGT is the limiting factor), or idling in traffic for 2hrs makes no difference.

I have radiator and intercooler mods on the way (as well as a good clean), so will do some more work in the next few months.

I have an unused sensor bung from the 1Gauge kit I bought a while back .. welding it to the trans sump now seems like the best use for it.
I also have the extended T/C sump(when the TC was changed over), so fitting a sensor to it is easy.
The hard part is to figure out what gauge to use, and ideally I'd love to use the 1Gauge, as I like the data logging ability.
But it has no more slots. All 7 used up.

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