607 4HP20 auto trans temp sensor fault and other issues

[Mandrake]

Most likely the oil/coolant heat exchanger is blocked on the water side allowing overheating of the oil. I had this problem on my first Xantia V6 where the gearbox ran about 10-15 degrees higher than it should.

After a while the oil would get burnt and the torque converter would start to shudder. Symptoms could be reversed by doing multiple oil changes but would reappear after a couple of thousand miles when the oil burnt again.

Other symptoms are that on hard acceleration the temperature rises quickly (mine went as high as 108 degrees and 105 was common) but falls very very slowly once you are crushing again, staying 10-15 degrees above coolant temperature.

When the heat exchanger is working the temperature shouldn't go over about 96 degrees even when driven hard and should rapidly drop back to about 90-93 when cruising. (Within a minute or two)

The gearbox in that car failed about 6 weeks after I got rid of it...

My current Xantia V6 gearbox runs about 15 degrees cooler, staying between about 88-94 most of the time and cools very quickly after hard acceleration ends, which is a good sign the heat exchanger is working.

[Franchute13]

Hi.
Thank you for your answers.
Today call 2 specialists in repair of automatic boxes. Both told me that the problem has to be the converter and that's why it raises the temperature.
I'm going to take the car to one of the specialists for analysis.
Thank you.

[mickeymoon]

I'd believe Simon's theory over pretty much anyone given the amount of fault-finding he did!

Sent from my SM-G925F using Tapatalk

[Mandrake]

The only thing that could be wrong with the torque converter to cause overheating to 110 degrees as far as I know would either be that the support bearing (which is just a white metal bush I think) is seizing up, or the lockup clutch has disintegrated.

If the support bushing is seizing up and starting to turn in the housing it will make a funny noise that sounds like, well, a bearing turning in its housing, every time the torque converter locks up - noticeable if you accelerate slowly in second gear and listen for an odd noise. My old V6 had that noise for a long time before the gearbox finally failed, and when it did fail it spun the bearing in the housing, which makes a horrible noise!

The other thing that could go wrong in the torque converter to cause overheating is either the lockup clutch linings have disintegrated, or it is not locking up at all. If it is not locking up at all (which could have multiple causes, including problems in the valve block) then the torque converter will generate more heat than normal because of the converter slip - the 4HP20 is designed to lock up the torque converter where possible to minimise heat generation and maximise MPG and in particular if the oil is overheating it will lock up the converter as much as possible to prevent further temperature rise.

If the torque converter seems to work in both open mode (it doesn't stall at idle etc) and also locks up fully at higher RPM, I don't think it will be that. Go into 2nd gear and bring the rpm up to about 4000 rpm and hold it there for a couple of seconds - after that it should be locked up, then punch the throttle for a second, it should take off like a manual gearbox without any torque converter slip. If it does, and the torque converter transitions smoothly between unlocked and locked (accelerate slowly in second gear to test this - at about 2500 rpm the rpm should start to drop for the same road speed by about 500 rpm) I doubt the torque converter is the problem.

If the problem was excessive heat generation in the torque converter and the heat exchanger was OK, it might get hot under hard driving (not over 100 degrees though!) but would quickly cool down when you went back to a steady cruise. On the other hand if the torque converter is working normally but the heat exchanger is blocked it will also get hot quickly under hard driving, but will be extremely slow to cool down when you go back to cruising.

The main test to see if the heat exchanger is working is to evaluate how quickly the oil temperature drops to within 5 degrees of the coolant temperature when you ease off and go back to a modest speed cruise.

Try to find a long motorway speed hill that is a couple of miles long - have someone monitor the temperature on the Lexia while you drive, get the gearbox hot by accelerating hard up the hill, when it is up to the temperature you're worried about, turn around and cruise down the hill at say 60mph with a light throttle and watch the temperature. If it drops quickly (down to <95 in less than about 2 minutes) then the heat exchanger is probably OK. If it drops very slowly (still well above 100 degrees 3-4 minutes later) the the heat exchanger must be blocked, as the oil temperature should come down to within 5 degrees of the engine coolant temperature within just a couple of minutes of easing off the speed/acceleration.

[Franchute13]

Thanks for your time
On Saturday I do the tests.

[Franchute13]

Hi.
Sorry for the delay.
I did a test today. It is not the test described by Mandrake.
I did 30km at a speed of 80km / h - 90km / h. Then park the car and check the temperature using a Lexia cable with the engine running. The temperature was 103C and it was not going down.
Can this still indicate a problem in the heat exchanger?
Thank you.

[Franchute13]

I read in the manual that says:
Transmission operating temperature: approximately 100C.

[elma]

You can get tiptronic on a 4HP20?
Is that something a Xantia can be gifted with?

[Mandrake]

Hi.
Sorry for the delay.
I did a test today. It is not the test described by Mandrake.
I did 30km at a speed of 80km / h - 90km / h. Then park the car and check the temperature using a Lexia cable with the engine running. The temperature was 103C and it was not going down.
Can this still indicate a problem in the heat exchanger?
Thank you.

Yes I would say that probably does indicate a problem with the function of the heat exchanger, however there are some things to consider with your version of the test before drawing this conclusion:

1) At idle the oil pump in the gearbox will be pumping oil at about half the speed that it would at 100km/hr. Also the water pump in the engine will be pumping coolant at about half the speed. So the effectiveness of cooling the gearbox will be reduced.

2) The coolant temperature will be higher at idle after a high speed trip - it will be somewhere between 93-97 degrees, because the slow fan speed doesn't come on until 93 degrees and the fast fan until about 97 degrees, whereas at 100km/hr but with a light throttle the coolant will be more like 88-93 degrees due to the natural airflow through the radiator that does not require help from the fan.

So what you need to do is also measure the engine coolant temperature with the Lexia after your test and compare it with the gearbox oil temperature. If your coolant temperature is around 93 degrees and your gearbox oil temperature remains at 103 degrees even after a few minutes of idling the heat exchanger can't be working properly, as after just two or three minutes the gearbox oil temperature should drop to within 5 degrees of the coolant temperature.

I read in the manual that says:
Transmission operating temperature: approximately 100C.

Yes I've seen this quote in the technical manual of the 4HP20, however it does not give any information under what conditions 100 degrees might be expected, and whether that is the maximum temperature to be expected under severe conditions or the average temperature of normal operation.

In my opinion 100 degrees would be the maximum expected in severe conditions. On my current Xantia V6 even when I drive the car hard with lots of acceleration and high speed to deliberately try to heat the gearbox it never goes above 96 degrees, and normally it stays between 88 and 94 degrees. More importantly when it does heat up to 96 degrees, as soon as I slow down and ease off the temperature drops quickly down to about 90-92 degrees. (Within a couple of minutes) This shows that when the source of heat is removed the cooling system cools the oil quickly.

On my old Xantia V6 the oil temperature was always above 100 degrees even when driven normally for some time, and temperatures as high as 105 degrees was common. (The highest I saw was 108 degrees) More importantly when easing off and slowing down the temperature would only drop very slowly - several minutes later the temperature would have only dropped from 105 to 103 degrees for example, and it took a long time to go below 100.

I would check your coolant temperature reading using the Lexia just to be sure you coolant temperature isn't unusually high (for example the slow fan speed might have failed) but if the coolant temperature seems normal (93-97 when idling, or 88-93 when cruising) then it does point towards the heat exchanger.

By the way, every few degrees increase in average oil temperature of the gearbox can shorten the life of the oil and/or gearbox quite a bit:

http://www.lubegard.com/pdfs/HeatChart%28AL-516%29.pdf

Keep in mind those figures are in Fahrenheit.

[xantia_v6]

Personally, I think that the heat/failure chart linked above is just unsubstantiated marketing crap.

Also be aware that ambient temperature has a significant effect on oil temperature, as quite a bit of the cooling is through the case of the transmission. In a hot climate you will normally see higher temperatures than in Scotland.

[Mandrake]

The specific temperatures and estimate lifetime shown in that chart are certainly up for debate (I think they're a little pessimistic) but the trend is valid and there is no doubt that overheating of the oil will burn the oil causing permanent disintegration of the oils properties and possible damage to the clutches due to the oil no longer performing as it should.

I have first hand experience of overheating/burning oil in a 4HP20 and its amazing how quickly it goes black and starts causing symptoms like torque converter clutch shudder, and I have also seen first hand that frequent oil changes can temporarily reverse the clutch shudder but it quickly returns again (just a few thousand miles) when the oil is constantly overheating.

Franchute13's original post said he is seeing temperatures as high as 110 degrees just driving normally at 100km - I never saw temperatures quite that high even on my bad 4HP20, the one that was burning the oil quickly. I bet if an oil change was done on his box that the oil would be completely black.

It's true that in a hotter environment the normal operating temperature may be a little bit higher - but not much higher because the coolant temperature of the engine is the main thing that regulates the gearbox temperature, and that is regulated with the thermostat and fan control. There would be a lot more cooling via the heat exchanger than just from the casing of the gearbox, otherwise it wouldn't cool down so incredibly slowly when the heat exchanger is blocked. The main thing that the casing of the gearbox provides is thermal inertia, not heatsinking ability.

Finally, I don't base my temperature figures on a single car, but the comparison of a known bad and known good 4HP20 - driven by the same owner, in the same locale in the same weather on the same roads, both measured scientifically using a Lexia. And the difference between the two cars was 10-15 degrees for the same driving conditions.

The bad 4HP20 ran between 102-108 degrees once warmed up and cooled very slowly after the load was removed. It did not track the coolant temperature. The good 4HP20 runs between 88-94 and cools quickly when the load is removed, and does track the coolant temperature quite closely, never more than about 3-4 degrees above coolant temperature.

A fault in the gearbox (slipping clutch etc) that generated an unusual amount of heat could also cause excessive running temperatures under load, but the heat exchanger should still be able to cool it quickly when the load is removed - eg coasting or idling at a standstill. For me the smoking gun is that when the load is removed the temperature falls very very slowly - which is exactly what I saw on my bad 4HP20.

So my opinion is that the heat exchanger is not working. It's up to the OP to decide what he does with that opinion.

What I do know is that if it continues to run at that temperature all the time the oil will get burnt (if it isn't already) and after not too long damage to the gearbox will be done.

[Franchute13]

Hi.
Thank you for your answers.
I have a friend who has the same car as me. We will go to test your car to see what temperature marks your gearbox.
On the other hand, I will look for where to buy heat exchanger.
Thx

[Mandrake]

Hi.
Thank you for your answers.
I have a friend who has the same car as me. We will go to test your car to see what temperature marks your gearbox.
On the other hand, I will look for where to buy heat exchanger.
Thx

If you have a friend with the same car definitely put the Lexia on his car and drive the same test route as your car to get a comparison between the two cars. Make sure both cars get time to fully warm up, and ideally try to test them one after another on the same day. (Same weather)

Let us know the results.

[Franchute13]

Hi.
Thank you for your answers.
I have a friend who has the same car as me. We will go to test your car to see what temperature marks your gearbox.
On the other hand, I will look for where to buy heat exchanger.
Thx

If you have a friend with the same car definitely put the Lexia on his car and drive the same test route as your car to get a comparison between the two cars. Make sure both cars get time to fully warm up, and ideally try to test them one after another on the same day. (Same weather)

Let us know the results.

Of course!
My friend is traveling, I hope I can do the test on Saturday 27. I will tell you.
My car will be parked in the garage;)

[Franchute13]

Hi.
Today we did the test. We used the 2 cars.
Same route, same speeds (90km / h - 120km / h). My car showed 12 C degrees warmer on the box oil. (94C vs 106C).
I must have the heat exchanger faulty.