Have I been running with too much transmission fluid

Pulled the tranny modulator off and it poured out fluid - was not expecting that. Checked the tranny fluid level and it was off the chart, at least according to the dip-stick.

If indeed I have been running with too much tranny fluid, what’s the damage gonna be?

Would there be any reason to add too much fluid to cover a problem?


^^^ That’s a Holley modulator

^^^ That’s a clean tranny dip-stick

^^^ That’s WAY too much fluid on the tranny dip-stick I think

^^^ That’s the hole the tranny modulator and all the fluid come out of

^^^ That’s all the fluid the came out of the modulator hole - maybe two quarts

You checked it with the car idling? Per the usual procedure?

Did you check it car warm, having been driven to operating temp, engine still running, on a level surface? If so, you’re overfilled. If not, check it properly.

So… you can only check for the correct transmission fluid level if the Jag is able to run? What if the Jag’s been sitting for a while and you wanna make sure things are good before you go and fire her up?

There have been instances where the fluid in the torque convertor has leaked back into the transmission, I had that happen to a S11 XJ6, that would lead to a much higher reading on the dip stick.

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You make sure the fluid shows at least minimum on the stick. It might be higher, even higher than maximum, for the reason Robin mentioned: drain back into the pan after a long lay-up.

This ‘overfill’, if caused by drain back, will, be gulped-up by the transmission pump within moments of starting the engine so check the fluid again. Add fluid if needed but do fill to the maximum leave. Leave it just above “minimum” and recheck when the fluid is hot…10 miles of driving or so.

The fluid expands with temperature. If you top-off right to maximum when cold or merely warm it’ll be over-filled when hot,


What Doug said. I’d leave it as is, then once started and warmed up, check as Jon outlined.

Fluid can also drain back from the cooler in the radiator as the fluid there is higher thsn the line connections on the tranny.

There is a cold and hot measurement on dipstick.

When cold, it should be near the cold mark, but that’s not accurate.

With transmission warmed up (20 minutes of driving) it should be a wee bit below the max hot.

Too much fluid causes foaming which is not good. Read up about it. Luckily these TH400s are tough. But you may have taken a bit of life out of it.

FWIW, I’ve drained my pan a few times, when cold, it should never be above top of pan.

Just to close this thread out…

Checking the tranny fluid without the engine running on my TH400 provides no good info on fluid level - the dipstick in this state always shows fluid above the max level for whatever reason.

When running, the dip stick is accurate on a cold check - showing fluid near the correct levels on the dipstick and then correctly when warmed up.

All good in my case.

And that’s all I got on that - thanks everyone!!

  1. There is no point in checking the tranny’s fluid level without engine running.

  2. Following engineering safety design rule (from that era) - if the fluid is at least on the end of a dipstick with engine on idle - your tranny will be safe and hot/cold marks are not relevant ( it will fit somewhere around minimum)

  3. Following engineering safety design rule (from that era) - even if you’ll top up to the max level with engine off - during engine idling - you will still get somewhere between pt.2 and maximum

  4. As mentioned above, during ‘seasoning’ off the road for a long time - the fluid may/will find the way from the torque converter into the sump pan.

  5. Whean seasoning as per pt.4 it is highly recommended to top your tranny up with extra quart or two above the max level on the dipstick (*checked with engine running)

  6. Following engineering safety design (from that era) - all the excess of fluid will be evacuated via vent on top in a spectacular surprise-show during warm-up. The only thing that moves fast during the idle when stationary - is your input shaft and hydraulic pump. Same safety design gives reassurance that liquid will be thrown out while you’re warming it up (thermal expansion) accelerating.

  7. Your gearbox liquid looks like pile of suffering, laternatively - like it’s been serviced by true Jaguar Lover. There was a good time to change it… 60k miles ago I assume. Frankly, TH400 was also mounted in a Humvee…

  8. It seems reasonable to know how to check the fliud level in XJS prior to starting any job on the gearbox. Just saying…

  9. You’ve used clean container for the old gearbox fluid, I bet you were not planning to change it :slight_smile: