[Dry Clean]

You know nothing, water needs room to move/mix the water at the top of the tank will slap about but the water at the bottom wont be moving, now stop talking nonsense this is basic science.

I reckon if you put a few drops of coloured dye into the top of your tank and went for a drive, the dye would mix all around the water and not just stay at the top.

The diurnal flux created from the kinetic energy of the van's movement would ensure this happened.

Basic science innit.

Not really, you might get a small amount of movement between the different water temps but you certainly wont get
a mixing effect plus your going to get very little kinetic energy until the tank has been emptied enough to leave room for the water to move, this will also be reduced by the baffles.
All the  van movement would be doing is creating a wave effect on top of the water which would have very little effect on the water at the bottom of a 500 or 600 litre upright tank.

[AuRavelling79]

Sorry Dry Clean - my experience is different.

Since 2010 I have put 3KW immersions in a 400 a 200 and a 650 tank (current).

Whether full or not, by the time I get to my first job (anything from 1 mile to 10 miles) I get warm water to the brush head.

Never been an issue. Convection and movement does the job.

[Dry Clean]

Sorry Dry Clean - my experience is different.

Since 2010 I have put 3KW immersions in a 400 a 200 and a 650 tank (current).

Whether full or not, by the time I get to my first job (anything from 1 mile to 10 miles) I get warm water to the brush head.

Never been an issue. Convection and movement does the job.

I'm not saying your not going to get warm water at the brush head especially with your set up (3kw heating 650ltrs of water )
even the cooler water in the bottom of the tank should be warm enough, it becomes more of a problem when you are restricted
to weaker heaters.