Hi All,

Once again I seek the sage advice from all the good people here :-)

Recently my auto transmission started to play up and was very reluctant to change gear...it also felt [no other way for me to describe it] like it was in "thick fluid". This has only ever happened when the car is very hot [see babble below] or when the car has been on a long journey.

When the car is cool the transmission seems fine, no reluctance to change gear, no cludginess/"thick fluid" feeling - performs well.

I recently had problems with my car overheating due to a failed fan. I had this replaced by a Jag dealer who also checked my cars fluid levels, pressure tested, checked thermostat etc etc. Everything was just fine for a while.

Since then, and only once, in hot weather I was stuck in traffic for about 45 minutes and the car temp slowly started to rise, but fell as soon as I started to move. This has only happened once in the past couple of months so I'm not sure if I should be worried (or how much I should be worried).

Does the dash temp gauge also reflect any overheating in the auto-transmission?

Any advice or comments welcome.

Regards,
Troy.

 

The dash gauge doesn't even reflect engine temp, much less transmission. Once it reaches 185 deg it stays there until about 230, then goes quickly into the red. If you saw yours going up, you're lucky you didn't lose the engine.

The fans should come on beginning with low speed at 205 deg. Turn your AC on and see if the fans are running. If not you definitely have a problem. Check the relevant fuses and relays.

The transmission cooler is combined with the radiator, and it mat overheat if the radiator coolant temp. is too high. You don't say how many miles are on the car, but the transmission fluid may be damaged from overheating.

You will be able to monitor the engine temp. with various phone apps, or add on gauges like Ultragauge. But my preferred solution is Realgauge from whitexkr. His website is thejagwrangler.com

 

Yes indeed, the gearbox oil is cooled by a heat exchanger through the radiator.

If the gearbox gets too hot the electronics will prevent it from shifting up, that way it makes more revs and is cooling the oil more rapidly. Can be it shifts around the 4000 revs mark, when you get out of traffic and you're able to maintain speeds like 70 mph it will eventually shifts up and act normal again.

There is a temp sensor in the gearbox which gives a signal to the electronics saying it's getting too hot. This is quite normal for an ZF 5HP24 gearbox.

 

It's possible that chronic engine overheating could also make the transmission run too hot. The transmission oil cooler will also have the reverse effect, I think, with a very hot engine.

What you really need to do is fix the engine overheating, immediately and properly. There's a chance that you haven't yet caused serious engine damage, although it's not a high one. Don't drive it again until it's fixed.

 

Thanks everyone for your comments, I'm getting an OBD sensor (initiated by RJ237's comments) so I can see exactly how hot the engine is getting.

The car has only overheated once and hasn't shown any of the signs it did before, ie. the fans running when the engine is off, the transmission issue. The expected fan behaviour is also correct, ie. AC on and fans kick-in etc.

...saying that, there is obviously a problem so I'll use the OBD to get an accurate read on the temperatures and let you know how I go :-)

Troy.

 

The problem with modern temperature gauges is that they can hide chronic overheating, until it's too late and the damage is done. Discoverys are the worst, the guage reads normal up to 250F!

 

you may need to change this

search my old post about the gear shifter issue. I had the same overheated warning on my dash at that time

 

An update,

I've purchased an ELM327 OBD2 Bluetooth adapter and it works with some basic sensors, eg:

Engine RPM
Calculated Load Value
Coolant Temperature
Fuel System Status
Vehicle Speed
Short Term Fuel Trim
Long Term Fuel Trim
Intake Manifold Pressure
Timing Advance
Intake Air Temperature
Air Flow Rate
Absolute Throttle Position
Oxygen sensor voltages/associated short term fuel trims
Fuel System status
Fuel Pressure

...there not a lot there but for $15 its pretty good

Is the coolant temperature sensor an accurate sensor for the engine temperature? It's possible there are other sensors that the cheapo OBD2 reader can't see.

Does anyone know what acceptable range for the coolant temperature is?


Troy.

 

There is a current thread in the XK8 / XKR ( X100 ) forum discussing the same thing - They have the same engine.
https://www.jaguarforums.com/forum/x...rature-138312/

 

Thanks Craig, seems like there may still be a problem with the cooling system, it's creeping up when stuck in traffic :-(

...back to investigate.

 

I've used a OBDII bluetooth device to check the coolant temperature and discovered that as soon as I am stationary the temperature begins to creep up.

After driving for about 30mins I then hit some traffic, as soon as the car was idling it began to rise until it hit about 101°C/214°F - at which point I entered some free flowing traffic [motorway] and the temperature dropped to about 88°C/190°F.

Based on the following:

• Both fans are running (recently replaced [used] due to previous fan damaged)
• Pressure tested by service centre
• Temperature reduces to normal while driving

...I'm assuming the problem lies with one of:

• Airflow through radiator
• Radiator
• Water pump

...maybe time to book in for a service...