607 4HP20 auto trans temp sensor fault and other issues

[Mandrake]

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.

My current Xantia V6 also peaks at about 94 degrees under high speed and acceleration, so I think your friends cars gearbox oil temperature is normal. 106 degrees under the same driving conditions is not normal and is about the same temperatures I was seeing on my old Xantia V6 with the overheating gearbox which was burning the oil all the time and eventually failed.

So your gearbox is definitely overheating, it just remains to confirm whether it is due to a blocked heat exchanger as we believe or if it is a more serious problem inside the gearbox. If it is the heat exchanger and you can get it properly unblocked or replaced you might get away with doing that and doing some oil changes to dilute any burnt oil, hopefully there is no permanent damage to the clutches in the box.

You would also need to find why the heat exchanger was blocked - it would only block if the coolant was poorly maintained or someone used some stop leak in the coolant - on the Xantia V6 it's very common for the coolant expansion chamber to split around the seam and leak under pressure, so I suspect a lot of people put stop leak formulas into the coolant that then block the heat exchanger and cause the gearbox to overheat.

If the problem is not the heat exchanger and is something in the gearbox then there is probably nothing you can do about it as it won't be economic to rebuild.

[Franchute13]

Hi Simon!
Thank you for responding and for taking the test in your car.
When you changed the oil burned in your old Xantia, it came out dark?
Thank you

[Hell Razor5543]

I saw the pictures Simon posted on the forum, and the first oil change was somewhat dark (black as SIN!).

[Franchute13]

Hi.
I buy the heat exchanger. Now I have to wait 30 days for it to arrive
When it is installed I re-test and write the news.

[Mandrake]

Good luck. Remember to check the oil level in the gearbox afterwards as you will probably lose some and the level is quite critical. If you don't have the procedure for checking it let us know, as there is a document floating around with the proper procedure, which includes measuring the oil temperature with the Lexia as the oil level is checked at a specific temperature with the engine running in neutral. You'll also need some perfectly level ground to park the car on when checking the level as even a small slope will cause a large error in getting the level correct.

[Franchute13]

Hi.
Heat exchanger changed. I could do a short tour to try and the temperature never exceeded 94 !!!
This Saturday I do an extended test and I comment again.
Regards!

[CitroJim]

Excellent! Fingers crossed (for luck) the problem is now solved

[Mandrake]

Hi Simon!
Thank you for responding and for taking the test in your car.
When you changed the oil burned in your old Xantia, it came out dark?
Thank you

Here is a picture of the oil that came out each time I changed the oil, numbered 1 to 4. There were a few hundred miles driving between each change to allow mixing. On the far right is new unused oil straight from the bottle for comparison. As you can see it wasn't until the third change before the oil started to change from black! So one oil change on its own will not do much if the oil is really black.

Hi.
Heat exchanger changed. I could do a short tour to try and the temperature never exceeded 94 !!!
This Saturday I do an extended test and I comment again.
Regards!

Excellent! Fingers crossed (for luck) the problem is now solved

Yes that's excellent news, fingers crossed. When working properly the gearbox oil temperature should never really go more than a few degrees above the current engine coolant temperature, and in fact the gearbox oil temperature is affected more by changes in engine coolant temperature than it is by load on the gearbox.

I was thinking about what goes wrong with the heat exchanger Jim, and I realised that it's not necessary for the water side to be completely blocked and not able to flow at all, if the heat transfer fins inside are coated with a thick layer of insulating gunk like certain kinds of congealed radiator stop leak, it will not be able to transfer heat effectively even though water is flowing through it.

Franchute13: when you removed the old one, did you find that the water side of the exchange was blocked completely ? Or if it was not, could you see any layer of gunk coating it inside ?

Also have you done or do you plan to do any oil changes ? Although changing the heat exchanger should prevent it from overheating and prevent further damage to the gearbox or oil degradation, some symptoms of the gearbox will probably remain until the oil in the box is cleaner, and it may take 2-3 changes to get it sufficiently clean for any symptoms to go away. As you can only change about 50% of the oil each time you drain it, you are diluting dirty oil with clean oil by 50% each change.

[Mandrake]

Another thing occurs to me - if the heat exchanger was blocked or coated in gunk - how did it get that way ?

Have you owned the car for long and have you done a coolant flush and change since you owned it ? I would be inclined to do a full coolant flush and change in case any old stop leak gunk is still in the coolant system - you wouldn't want it to gunk up the new heat exchanger!

If you've already changed the coolant recently and you have not added any stop leak additive to the coolant yourself you should be ok.

[CitroJim]

I was thinking about what goes wrong with the heat exchanger Jim, and I realised that it's not necessary for the water side to be completely blocked and not able to flow at all, if the heat transfer fins inside are coated with a thick layer of insulating gunk like certain kinds of congealed radiator stop leak, it will not be able to transfer heat effectively even though water is flowing through it.

That's a very good point Simon... The one I had was definitely well blocked though, only a dribble of water could be persuaded to flow through it but knowing the consistency and formulation of some sealants a coating of stuff is quite possible.

I regret now never chopping the duff cooler open to examine its internal construction...

Also, I wonder if a build-up of scale in the cooler - as you have encountered around the thermostat on your V6 - could also potentially cause this issue?

Another thing occurs to me - if the heat exchanger was blocked or coated in gunk - how did it get that way ?

Have you owned the car for long and have you done a coolant flush and change since you owned it ? I would be inclined to do a full coolant flush and change in case any old stop leak gunk is still in the coolant system - you wouldn't want it to gunk up the new heat exchanger!

If you've already changed the coolant recently and you have not added any stop leak additive to the coolant yourself you should be ok.

Good thinking!

[Franchute13]

Hello!!
The automatic box worked perfect !. Never exceed 94C on a 50km journey !.
Now I have another problem but I will create a new thread.
Mandrake, I have the old exchanger and I'm going to open it to tell you what's inside!
regards

[Franchute13]

Hi.
Finally the 4hp20 fails completely.
The heat exchanger was completely clogged.
In these images we can see the pieces that broke and dropped particles. (part nro 4, 10, 11)
regards

[admin note:-] The attached images were lost during a server malfunction. Please upload them again, if possible.

[Peugeot_Russ]

"I left the car to cool down with the bonnet up and went and had some tea and put kids in bed etc. "

lol . the British really do love their teas.