what could make an auto box get hot??

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robpenrose

robpenrose

New Member
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482
Location
Surrey or Cornwall
Got an issue, living in the french alps and on some long hill climbs, i get the auto hot temp sensor come on, comes on flashes intermintently then usuall stayes on until the road flattens out. sometimes takes ages to go out. Also had it on in the UK, but on not particularly long hills. Every time disco goes to garage i get them to check oil level and so far its always been fine. (Oh and also had it come on when going down a steep hill too, whats that all about??)

So is there a reason its getting hot? I could understand if i were pulling a 3 ton trailer up in 30 degree heat, but its just the car in usually minus temps.

It worrys me cause i dont want to cook the box, but even if i stop and let it cool for a while, doesnt usually make much difference.

I have noticed it does sometimes come on when i hit a bump, but the roads are crap, bumps everywhere so could just be a coincidence.

Everyone just says prob a dodgy sensor, but is there anything internally that could be worn which is generating alot of heat?

TD5 and done 102,000 miles
 
If it comes on during bumps maybe it is just a dodgy sender - but this is not common.

Check transmission cooler fins up the front are not clogged or blocked.

Oil might be OK but has it been replaced with the cooler flushed out etc...?

Try this, doing it properly where you feed in new fluid while letting it come out the cooler return so you can get ALL the fluid out and changed - or take it to a garage who will use a pump to force new stuff through the system.

Might be worth dropping the oil, taking the pan off and checking for bits of gearbox and check the oil filter isn't blocked too.
 
I'd also check the engine oil cooler, right hand side of the radiator. Check that the rad fins aren't blocked or blown out at the back. Garage changed my head, before I noticed that the rad was U/S. I'm working on the principle that the engine might be getting too hot, and transferring that heat to the gearbox.

'cos of the bump situation I'd also check all earth points.
 
Does your engine read hot as well as the trans temp light , if not then check temp at trans oil cooler on front with laser temp guage (easiest)
It could well be just dodgy sensor , very unlikely that temp is being generated quickly in trans as you would get other symptoms eg sloppy changing i.e. not positive engagement from gear to gear felt as slip .
Do you manually shift to hold lower gear and travel at moderate revs or do you just let it sort itself out ?
 
Last edited:
The ONLY source of heat generation of any significance in the auto box is the torque converter.

The rest of it will make a little warmth, but not a lot, UNLESS a brake band or clutch pack is slipping badly, but you would notice that as a BAD fault.

The TC acts as a calorimeter and the trans fluid in it heats up as it sloshes around under great pressure and velocity. This happens worst under strong DRIVE at under 2,000 rpm or so, and under prolonged engine braking - steep descents.

If you are driving a lot in conditions where the TC LOCKUP CLUTCH won't come into operation, the trans fluid will get hotter and hotter, and may get so hot it starts smoking, and even goes on fire. I saw a Jag do that long ago.

You must check and probably replace the temp sensor, after which you may need to give consideration to fitting a much larger transmission oil cooler, and possibly one which uses the radiator return flow as a coolant medium - an oil to water heat exchanger. Thoes are VERY fast to cool the oil.

Whatever, you will do well to keep an eye on this so you don't melt the transmission.

CharlesY
 
not sure how common it is but mine flashes on going over bumps, when its cold,

i suspect the sensor or a trapped wire

get it replaced as a first port of call, or disconnect it as an unnecessary device, cant think of any thing else which has one #?
 
re prev post , it is not a uneccessary device , and lots of vehicles with auto trans have overtemp warning .
If you find temp sensor defective , in view of your use full synthetic trans oil would be a good idea as it can handle higher temps much better .
If engine temp is rising then suggested heat exchanger prob a good move .
Having said all above using 3.9V8 auto heavy towing in OZ the standard landrover system coped ok , but I did use manual overide on long climbs
 
it may not be unnecessary if you dragging a cement truck across the Oz desert,

but the op is getting no symptoms indicating hot box,has enough oil and would therefore be a lot happier if he took the wire off
 
cool thanks for all the responses and appologies for the delayed response.

Engine sitting normal tenp, gear changes all sweet and clutch slip/torque conver seems normal.

I will have a look at everything mentioned
 
I have just driven back from the Alps and had exactly the same problem. With 5 in the car and an additional 200KG of luggage I started getting the gearbox overheat warning light after a couple of hours of motorway traffic coming back through Chambery.

It then came on if I went quickly. To keep the light off over the next 500 miles I kept the speed down to 65 ish.

It did flash on occasionally during long uphill sections and also engine braking down to peage sections.

It was pretty worrying thinking I might have to stop at the side of the road. I phoned my mechanic in the UK and he just said keep the speed down and check for any oil leaks - which I couldn't see. I am getting him to check it over this week.

It is reassuring that others have experienced this.
 
The V8 automatics use a larger diameter torque converter than any of the others.
It may well be that it can handle driving and braking better than the TD5 converter.

It might be interesting to try a V8 converter on a TD5. It would keep the revs down as the car picked up speed.

Hmmmmmmmmm..................

CharlesY
 
I have been having the same problem here in New Zealand with my Disco tdi, took it to the shop and had the auto serviced but still had the overheating light come on now and again. Took it back to the shop and they stuck a sticker to the auto to record the temp and said to come back in the next time the warning light had been activated. Next day it happened again so went back to the shop and the sticker showed that the temp was well within usual limits so pointing out that it was a sensor fault. They did say that for the auto to be showing as overheating it would be so hot that if you touched your hand on the outside of the auto it would burn you hand straight away, ie it it would be bloody hot not just warm. So either get your nearest Auto shop to check the temp or try putting your hand on the auto the next time your warning light comes on, if its only warm then its just the sensor. Next thing is where is the best place to get a auto temp sensor for a 96 disco tdi over there in the UK, any ideas guys ???
 
If the auto hot oil light comes on the two places to check, imo, are:

1. The temp sensor itself, &

2. Replace the oil if not done in the last few months. Use a good quality Dexron III oil. You'll need about 5 ltrs.
 
i've had the same today except not under load (just me in the car and not towing owt). when the temp light came on the disco struggled to pull away at junctions etc and was vibrating like mad. Going to get it into an indi this week to have the oil and filters changed to see if it sorts it
 
Garage has said that the fluid is shot and has some contamination, so it's going to be flushed out, filter change etc to see if that solves the overheating
 
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