I had the dreaded bong of the transmission failsafe prog come up on my dash on Tuesday, and it appeared to only have 3rd gear. After searching on here i thought it was pointing to a blocked oil cooler, so today I took the oil cooler off and the pipes, the oil that came out was pretty clear red with no sludge or dirt in it. The oil seemed to be flowing out of it just fine.
The radiator and cooling system was all flushed and replaced with coolant about 4 months ago.
My question, is there a way of telling if the cooler blocked?
I’ve flushed the pipes through with fresh oil and it was coming out as clean as it was going in.
Many thanks in advance.

2004 vogue
Td6 5 speed auto gm box
200k miles

This type of oil cooler.
Also I can select low range and back with no problems.

Although I admire your optimism, the failsafe message is not related to overheating transmission fluid. You’ve probably read that, if the transmission fluid is overheating, the transmission ECU selects its ‘cooling strategy’ mode which inhibits upshifts to keep the engine speed (and therefore flow through the cooler) high. This does not result in the failsafe message being displayed. I’m afraid your situation is more serious. I would suggest that you remove your sump pan and check for metallic debris.

Phil

Overheating of the transmission is usually first noticed when it goes into an overheat strategy. It will try to hold onto lower gears for longer which increases the input rpm to the transmission so turns the oil pump faster and pumps more fluid around the cooling system to help bring temperatures down. If it still can't bring the temperatures down then it might go into a failsafe mode.
There are many other reasons why you can get a trans failsafe and a code reader is the only way of knowing for sure why it popped up (some can be as simple as a low battery voltage).

So assuming it is a temperature problem, did you check the water coolant passages of the oil cooler as I suspect it's those that will give the most issue not the oil passages.
The oil cooler is just a heat exchanger which uses the bottom few sections of the main coolant radiator to dump it's heat. It's usually the bottom of the radiator that gets blocked as sediment settles over the years which in turn also might pass into the oil cooler.
When mine went into an initial transmission over heat strategy one summer I changed the radiator and oil cooler (radiator had very small leak anyway). I've never had a problem since, must have been over 5 years ago now.
I don't think any amount of flushing of the radiator, even if removed to do it, will effectively clear the bottom few sections of the radiator.

If you've had a new recent radiator then I would look at the oil cooler water coolant passages...again assuming the failsafe is from an over temperature event...200k miles on a GM transmission is good going if not already replaced.

Editted to add...I see RRPhil has replied while I was typing mine, he's expert on the RR transmissions around here so ignore me lol!

Thanks for the reply.
I put it all back together this morning and topped the oil level back up. When I drove it it was changing gear as it should and then after about 3 miles ‘bong’ and we were back to what I’m sure is third gear, if I shifted across to manual mode I can down shift the 2 and then 1 and then back up but it won’t go past 3 although the dash says it’s in 4 and then 5.

Tomorrow I’ll pull the sump off and check it’s contents.
Phil if it is worst case and I need a new box can you recommend anyone in South Wales?

Hopefully your problem isn’t as serious as this, but a well known issue with the 5L40-E is the failure of the direct clutch drum and shaft assembly (the so-called ‘toilet roll shaft’) which allows the transmission to operate in all gears except 4th & 5th (i.e. the two ratios that require the direct clutch to be engaged).

Click image to enlarge

Click image to enlarge

Mine suffered the failure RRPhil says above:

Click image to enlarge

Click image to enlarge

I’ve taken my transmission out now, just trying to arrange a rebuild which is proving tricky in this current situation.
Is it a diy job? And which companies can supply the new parts that would be required?
Thanks guys

https://xoutpost.com/bmw-sav-forums/x5-e53...rdown.html

http://www.vanmatic.com/pwpcontrol.php?pwpID=8356

https://www.sussexautos.co.uk/auto-parts.php

https://jpat.co.uk/index.html

Phil