BW35/65 Checklist.

Hello Harvey and thanks for the good advice. Now, the dipstick on the B/W 65 in my late P6B carries one level mark and the word COLD. Does one observe the hot, idling, and 'been through all gears' procedure and fill to this mark, or is this mark intended to indicate a cold state with the engine stopped? It's presently, and has through my ownership, always been filled according to the former, but it's always had harsh changes too, regardless of how I adjust the kickdown cable.


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I've always done the former as well, hence it being in the "sticky" post at the head of this section, and I've never had any problems. That was BW advice as well, so I'm not sure why Rover put COLD on the stick. If you've had problems you think could possibly be caused by this I would suggest running though the same procedure, but straight after you've started the car from cold, and then see how much fluid you have to add, (if any) and then see if you notice any improvement with the harsh changes. I've never checked with the engine not running.

Have you got a fixed crimp on the kickdown cable?
I've just checked my book and it lists TQF, but no mention of the other specification at all. If you actually trawl through the factory WM it tells you to check the level in two different ways, in two different sections, and they can't both be right.

I always do them hot and running, and I'd never use any of the DEXRON fluids. They're fine for use in boxes designed to use them, but BW35/65/66's aren't.
Harvey, I'm a little puzzled about the use of Dexron II. A couple of years ago we had the BW35 box in our P5B fully reconditioned by a very good auto transmission specialist workshop. They refilled with Dexron II and when I queried this they were adamant that this was a suitable fluid. They did a lot of BW35s and never had any problems. We did fit a separate transmission cooler to eliminate any risk of contamination from the original radiator system and improve the cooling performance.

We haven't experienced any problems either (yet), but are not racing the old girl or towing huge loads either. Our usage would probably be considered "very gentle ".

Why is Dexron unsuitable and what effects would we expect to notice in use? Did the older Rover gearboxes have something different inside?


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Dexron had friction modifiers which allowed a small amount of slip on every change to smooth out the changes. All slip builds up heat and the boxes end up running hotter that they should, and the harder you use them the worse the problems gets. If a reconditioner tells you to use Dexron then for the duration of the guarantee then it isn't a problem, but afterwards, when any problems are down to you, I wouldn't use it. The clutch packs are borderline behind the Rover V8 anyway, I wouldn't give them an even harder time by using Dexron.

I know another good transmission specialist that says the same as yours did, but I beg to differ, and TBH, using ATF-G will always be safer than using Dexron.
Thank you for that clear explanation Harvey. I can understand things much better now.

Hpopefully the addition of the extra transmission cooler will keep our oil temperature down, although apart from starting off at traffic lights or intersections we very rarely find ourselves in anything but 3rd gear anyway. The gear changes whilst driving are normally quite rare.

Are there any compatibility issues between Dexron and ATF-G ? Is it OK to simply drain the box and refill with the other fluid?


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The problem is that the fluid that gets hot because of the slip in the clutches isn't cooled in any way while it's there, and has to go through the converter and be heated even more before it gets to the cooler.

Dexron and ATF-G can mix without problems. You will need to do at least 4 drain/refills before you can be sure of getting most of the Dexron out because it's not possible to drain the converter.