Hi all. Been toying with the idea of getting an MX5 for 20 years! Finally got a chance to buy one - I’ve seen a nice 2016 one that I’ve got my eye on. Something that’s stopped me having one is the rust issue. From what I gather, it affects the MK4’s too. After dropping 12k on the car, I will not be able to afford to underseal the car this year. Will this be a major issue? Will rinsing the underneath of the car be OK? Does anyone else have a 16 MK4 and haven’t undersealed it? Any advice?!
They are not that bad! Yet…but they will be very slowly working on it 
It’s not going to dissolve this year or next so enjoy it but try not to use it in salt laden winter days if you can & start popping cash in the tea-caddy (around £400.00 -ish) for next year if you are not doing it yourself. There are threads here showing how it should be done…eg splash guard strip downs. If it’s a keeper, do it.
If only for 2/4 years ownership personally I’d not bother but just hose it a bit after mucky sessions.
Scottishfiver gives good advice, typically rust starts to appear in a poorly looked after MX-5 at about 8 - 10 years. The MK-4 is young enough that we won’t see how it fares for a few yet, hopefully upgraded materials will prevent problems in some areas.
I’ve been involved in DIY undersealing 3 MK4’s now in their first year. The sub frames will look shocking in a few years though it won’t be structural until later so nothing to immediately worry about. Areas I would take particular care of when cleaning are rear arch rims and the area around the 1/4 panel at the front of the rear wheels. The rear arch does have a fibrous liner which I think could hold on to moisture over time, so an area for regular monitoring.
If you’re not keeping it long term then how much effort you make depends on how much you want to pay it forward.
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Thank you very much for your replies. All duly noted. It will be my daily driver and I’m looking to keep it for 5/6years. I’ll see if I can get it underseaked before next year, if not, definitely next year. Does anyone know of any good places in South Wales? (I’m based near Swansea).
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Sorry to resurrect an old thread but did you find anywhere in Swansea that would underseal your car? I need to get the new to us NC checked over and undersealed. Thanks.
Protection is something that can be done by yourself with the minimum amount of tools , just using the correct ones , procedure and products, the MK 4’s will and are the easiest to attack with this process at the minute being the newest but it does also all depend on where they have been living…I can help in guiding you to do this if needed , most of the problems we hit is down to lack of confidence, thats what we are here for …
Something to read…Jimbo's MK 4 RF in pearl white 7,000 miles - Mazda-Menders
The process is the same from a MK 1 to MK 4 with just slight differences, and the MK 4 being the easiest to do.
Contact me if i can be of any help.
M-m
Thanks MM, I’ll have a read of that and will formulate a plan, I should have mentioned my car is a 2006 MK3 with dubious / nonexistent history, hence the reason for me wanting to get it inspected, it was my Swansea search that lead me to this thread rather than the Mk4 bit.
Its the same process for a MK 3 , only they have been around a lot longer so will require more work to get right again, i would get her up in the air and have a good look around the underneath and if possible get a camera in to those box sections to gauge a plan of attack and whats needed, there will be rust 100% simply because of age and the good and old UKs answer to winter “salt”, it just depends as i have mentioned before it all depends where she as lived and use, most of the time it is just down to sorting all the underneath out form were there is untreated protected bare metal and were it creeps underneath the factory underseal in areas, worse case is sills and arches need cutting out and for fresh metal, then that comes down to you passion for the roadster, but once sorted and protected and staying on top of it ,that you have a roadster that will last .
If the protection process was done when new and fresh ,then you would have no issues , but hind sight is a wonderful thing with everything…any way here is a MK 3 i did for Ian…Mrs Mchattie's MK 3 - Mazda-Menders
All done on axle stands on a drive…
M-m