Standing by to be shot down!
I use a Karcher K5 washer on my cars, med pressure to initially clean off, snow foam, wash over with a mitt then finally rinse again on med pressure.
I know you don’t wash soft tops like this, but is there anything to be wary of with a PRHT?
No, it’ll be fine
I wash mine on full pressure, no worries (other than soaking neighbours car / house / passers by etc etc) 
Hmm, define ‘pressure’.
My Aquatak pressure washer is too powerful at 160Bar and the jet can excavate the cement between crazy paving slabs from up to a metre away. I need a special ‘patio cleaner’ attachment to preserve the surface on my concrete drive.
I don’t dare use it on a car, even with the softer rotary nozzle.
Sounds like common sense would prevail there then or a means to alter the lance tip to reduce the pressure…
Paging Suzi…paging Suzi…
That is the problem, can’t reduce the pressure with the tools available. And with confined space under a car distance is not an option either.
However for excavating the dried-on mud off a tractor or HGV, or cleaning the drains it is superb!
I always wear my Burberry jacket and Jimmy Choo boots when I get the Karcher out.
Time to get on down to B&Q for a domestic level pressure washer then rather than a concrete cutter.
Right tools for the job an all that…
Used a pressure washer on my last MX and it started to strip the paint of the lower sills…lesson learned, never again…but each to their own…
Which is why for the car I use an ancient all-metal lance (too useful and too durable to sell on the modern market) similar to this on the end of the garden hose, just mains pressure.
I would never use a rotary pencil jet on a car, that is asking for trouble. You need to get a fan jet nozzle, then 160 bar will be fine.
My 110 and 130 bar machines will damage concrete if you use the rotary pencil aggressively. I use the pencil nozzle to strip old stain off my decking too.
I use snow foam on my Mk6.5 NC 2.0 Sport-tech, which has PRHT roof. I sometimes wonder if the snow foam will clog up the drain holes. If it does, then any overflow of snowfoam/rinse water would overflow into the car I think. I’ve not noticed any wet carpets in the car after using it. Anyone had any problems?
No, never.
Why would you use a pressure washer on a car? A normal hose pipe is adequate. In my view a pressure washer forces water into places it shouldn’t be, into wiring light clusters and welded seams. Maybe ok for thick mud in wheel arches but not the rest of the car.
As our MX5’s rust quite easily over years, i can imagine the use of a pressure washer will hasten rusty cills and arches quicker than normal.
Hoods have a waterproof membrane under the surface and they can be penetrated by high pressure water, it’s a cumulative effect on canvas or mohair fabrics, PVC hoods don’t suffer to the same degree.
Only use for a pressure washer for me is applying SnowFoam products the car.
Well, I’d guess a bit of common sense would suggest not giving the jet end the full beans in the places you mention for the reasons you mentioned it…
My point is, why would you need to use one?
A normal hose pipe is inadequate in my experience, even with a hose gun they don’t shift much muck, they merely get the body wet. The reason for pressure washing (and snow foam) is to remove as much dirt as possible before doing a contact wash (this will greatly reduce swirls and dulling of the paint, because you are dragging less grime across it) - if you don’t care about fine scratches then you don’t really need to pressure wash.
The main cause of rust on cars is not water, it’s salt. The more of it you can remove, the better, and a pressure washer will assist. Obviously one does not spray a needle or pencil jet at a rubber seal or into a panel gap or at the light clusters - like any power tool a pressure washer needs to be used with care, so fan jets and 45 degree angles are the order of the day. I wouldn’t ordinarily recommend pressure washing a canvas roof, but I have a special low pressure attachment on my machine that shifts ingrained dirt without being harsh.
I have yet to see any ill effects of proper pressure washing - although an MOT tester did once jokingly threaten to fail my car for being too clean underneath. But each to their own of course, if you’re not comfortable doing something or don’t see the point of it, you’d be silly to then do it! And decent pressure washers with the appropriate attachments are not pocket money.
Pressure jets seem unnecessary to me.
I use a hose and jet nozzle, I rinse the car for 5 minutes first, then follow the 2 buckets technique, start at the top, with a shampoo/wax, so by the time I reach the lower body, muck has loosened up.