The usual procedure for flushing a cooling system is to drop the existing coolant (usually by disconnecting the bottom radiator hose) fill the system with distilled water and whatever flushing chemical the workshop uses, restart the engine, drive it around for a short time until everything is at operating temperature, dump the water and flush mixture and refill the cooling system with the proper coolant.

You can also simply flush the radiator (and not the rest of the cooling system) by disconnecting the radiator hoses and running a hose through the radiator, usually in the opposite direction the coolant flows. But this is a much more simplistic flush and doesn’t change the condition of the engine crankcase’s cooling passages.

It’s possible that the flushing process has loosened some rust or scale that then blocked the cooling system somewhere else (the thermostat is a prime suspect) and if that’s the case, the process needs to be repeated until the water coming out of the cooling system is nice and clean and not tainted with rust or scale or anything else.

Revving the engine to get the flushing mixture to do its job is not really a problem, but could also be achieved by actually driving the vehicle (which would also get it up to temperature faster). But, really, provided the temperature gauge hasn’t been allowed to move into the red zone, you shouldn’t have damaged anything. But you do need to know why the operating temperature of the engine is now higher after a cooling system flush.

This type of thing is certainly not an uncommon fault, but whether it’s more common in Toyotas is another question altogether. Certainly, Toyota has not recalled the vehicle to fix this problem, nor am I aware of a service bulletin (much more likely than a safety recall for a dud head unit).

But the good news is that there are specialist companies out there that fix problems like this one. You remove your head unit, send it away and it returns fully functioning and tested, ready to reinstall. Flickering and dropping out are both common faults in modern head units, but both can be fixed by the right specialist.

If the engine power has returned since this episode, I’d be willing to suggest that what happened is that the vehicle had gone into limp-home mode. This happens when something like the transmission or engine becomes hot enough that to continue at normal pace might cause damage to the vehicle. It’s the car’s way of saving its own life, if you like. When it does, you can expect a warning light and a reduction in power, just as you experienced.

Towing a caravan up hills is a great way to get a transmission really hot, or even a turbocharged engine such as the one in your LandCruiser. If the vehicle returned to normal once it had cooled down, then you shouldn’t have any ongoing problems, but another oil change and perhaps transmission service might be a good idea as these fluids can lose their mojo once they’ve been really hot even once.