Aut. Transmission behavior when hot

[oravla]

Hi,
I've an Opel Omega MV6 with the 4L30E transmission (it is also used in some BMWs). It was overhauled around 40.000km ago. It works perfectly, but when the coolant temperature is around 100°C for some time, the transmission starts to act strange. It stays in 1st until around 3.500rpm (even when accelerating gently) and then goes to 4th. This doesn't happen to often, only when the outside temperature is over 30°C and I've the AC on.

Why can this happen? I thought that maybe it is an electronic "safe mode" to try to cool the transmission down.
Could it be a fluid related problem? (wrong type, low quality oil or low level).

Thanks in advance

 

[wiswind]

How old is the fluid?
If it is old, it could be breaking down and need replacement.
I am not familiar at all with your vehicle, but most all modern vehicles need transmission fluid changes for the automatic transmissions.

I would verify the fluid flow through the transmission cooler(s).
When a transmission fails, it can result in a lot of junk going into the fluid....and becoming lodged in the cooler(s), blocking the flow of fluid through the cooler....causing the new / repaired transmission to overheat, and eventually fail.

The transmission can overheat without you knowing about it.

As you mention a coolant temperature at 100 degrees C, which is 212 degrees F, that sounds pretty hot.
My vehicle stays pretty steady at about 191 to 193 degrees F, as monitored by my scangauge that sees the same value that the engine computer sees.

When in stop and go traffic, I have the A/C on, which keeps the electric cooling fans ON, which maintains a constant airflow through the radiator....and results in a cooler coolant temperature.
You might want to verify that your radiator fan(s) are operating correctly.

My vehicle has a in-radiator transmission cooler that cools the ATF by a temperature exchange between the coolant and the ATF.
Hotter coolant will result in a hotter ATF.
Then I have a auxillary cooler mounted in front of the radiator.
The auxillary cooler is only really effective with air flowing through it.

Heat is the big killer of transmissions and the cause of fluid breakdown.
So, keeping fresh ATF of the correct specification for your vehicle, and keeping the fluid cooling working to it's best will help prevent problems with your transmission.

 

[Ramblin Fever]

I have this same transmission in a '97 Rodeo with currently 179k miles without a single flaw.

It sounds like possibly your's is either low on ATF, ATF is old/worn out; or it wasn't overhauled correctly. Many places are completely baffled by the GM 4L30-E transmission.

If your coolant temp is that hot, your transmission is overheating.

 

[JTK]

We had a few isuzus with 4L30Es as well. Range sensors can cause all kinds of shifting concerns on these trans. The TRS is bolted onto the gear selector shaft out the side of the case. A sure diagnosis of range sensor issues on this trans is; the PRND321 dash lights will jump around at random, thus confusing the heck out of the trans. You can remove, disassemble and clean and re-grease the wiper/board on this TRS.

Joel

 

[oravla]

Thank you for the answers.

I'll check the fluid level soon. I've also ordered the gasket+filter kit from ebay. This time I'm going to change the fluid myself. While I'm there I'll check the TRS.

wiswind: My engine is known for running hot. The coolant system works with high pressure and the normal operating temperature is between 90°C and 100°C.

 

[ARB1977]

My wifes 97 jetta transmission used to hold 3rd gear for alittle while then shift. I recently took it in to VW and had them change the filter and service the transmission...now its smooth as glass. May try that as long as the fluid isnt burnt.