ZF Auto box overheating....or is it???

**Juff** · 5th November 2012, 01:46 PM

I'm having trouble with my auto trans hot light coming on while driving up hills. It only occurrs when the average speed is around 40-50km/h. (So its working hard) I have not had a problem with it off road - low range work.(prob not working so hard)
I did cook the box and burn out the "A" clutch in it a few years ago and had it totally rebuilt as a result. (Pan gasket failure - wasn't happy!!) The guys who did the rebuild said it was the switch at fault at the time and rechecked the pump flow for me etc. I did change the switch at the time with an after market one and dont recall any further issues for a while...
My local LR mechanic also reckons they dont have a history of overheat so I think I am gonna try a new switch - Landrover will sell me a genuine one for $90.00 but before I get one, has anyone else had issues like this up hills or towing?

**SouthOz** · 5th November 2012, 06:05 PM

I bought 6 of these to fit to anything I want to check the temp on. I fit the sender under some foam and wrap tape over it. Works a treat. Ive fitted an aftermarket trans cooler to mine and am going to fit 2, one on each oil pipe.

Digital LCD Probe Fridge Freezer Thermometer Thermograph for Refrigerator 110

Dave

**sam_d** · 6th November 2012, 08:41 AM

My understanding is that the light will also come on if your auto-trans fluid levels are low. Have you checked to make sure that they are okay? It could be something simple like that.

DiscoMick · 6th November 2012, 08:06 PM

I only realised recently that the auto oil level has to be checked with the engine running, not stopped, which required extra oil. Might be worth checking.

**Juff** · 6th November 2012, 11:53 PM

Yeah best to check fluid level with engine running for sure!! I was not aware the light is related to level...as far as I understand it it's rigged to the temp sensor which is in the cooler lines between the auto box and the cooler in front of the radiator only....so there is a fluid level sensor somewhere as well?? Anyway this is not a level issue, engine running and checking it cold it's full on the stick... Gonna try and test the temp switch tomorrow to see if its coming on at the right temp....(if I can find what its supposed to come on at first!). Thanks for the input thus far, the investigation continues!!

**sam_d** · 7th November 2012, 09:11 AM

Originally Posted by Juff

Yeah best to check fluid level with engine running for sure!! I was not aware the light is related to level...as far as I understand it it's rigged to the temp sensor which is in the cooler lines between the auto box and the cooler in front of the radiator only....so there is a fluid level sensor somewhere as well?? Anyway this is not a level issue, engine running and checking it cold it's full on the stick... Gonna try and test the temp switch tomorrow to see if its coming on at the right temp....(if I can find what its supposed to come on at first!). Thanks for the input thus far, the investigation continues!!

The level sensor is part and parcel of the temperature sensor. There is also a possibility that the sensor is getting a bit old and might have developed a fault. I had this on my old Disco once (coupled with a dodgy connection) and the light would come on with 'ordinary' driving along the freeway even though nothing was actually wrong with the auto box.

**Discomark** · 8th November 2012, 05:50 PM

I had the same trouble with the light coming on on steep inclines and towing, low speed. Thought it was a faulty sensor but it wasn't and ended up with a full rebuild

The standard coolers are not up to towing etc and since I replaced mine with a P38 cooler it runs much cooler. From memory the light comes on at 130-135c which means the fluid is already overheated and its lifespan shortened significantly. Since I fitted the P38 cooler which is twice the size, the temp rarely hits 80c and normally sits at 48c on the flat in lockup. The other observation since fitting a digital temp gauge on the cooler line is how quickly the temp drops when lockup is reached, 20c in a few minutes dropped after lockup, this is said to be due to max pressure in the cooler lines and of course less friction due to clutches not working in lockup. its sometimes worth going to low range to get lockup sooner if possible, ive done this on really big hills and sand driving. Another consideration is switching to full synthetic fluid as it can handle the higher temps better
and in my experience seems to run cooler as well.
Cheers
Mark

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