Mazda5 Undercarriage condition - Your opinion on the rust?

Just bought this 2008 Mazda5 with 128,000 miles. Here's the undercarriage. Curious as to your opinions on the rust. Taking it to my mechanic for oil change and plugs so will have a better look and inspection when it's on the lift. Any spots in particular to watch out for and check out more closely? THANKS!

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sm1ke

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Canada
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'18 CX-9 Signature
Looks like a lot of surface rust, but nothing that would scare me off personally. Depends on what you're used to in your region - I live in an area where they salt the roads heavily every winter, so that looks normal to me, but it would probably be a surprise if you lived somewhere like Arizona.

If anything, I'd say that it'll be harder to break some bolts free if you ever have to replace anything on the undercarriage, so be prepared for that with some penetrating oil, elbow grease, and maybe a few extra nuts and bolts.
 
Looks like a lot of surface rust, but nothing that would scare me off personally. Depends on what you're used to in your region - I live in an area where they salt the roads heavily every winter, so that looks normal to me, but it would probably be a surprise if you lived somewhere like Arizona.

If anything, I'd say that it'll be harder to break some bolts free if you ever have to replace anything on the undercarriage, so be prepared for that with some penetrating oil, elbow grease, and maybe a few extra nuts and bolts.
Thanks--I'm in he Cleveland, Ohio area and they use salt in the winter.
 
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Mazda5gt
uhhh, considering what we've seen in terms of rust in the "rust belt", I'd go at least south of kentucky. that looks horrific, just imagine what the rust on bolts look like when you're ready to do a brake job.
 
So now I have 2 completely divergent opinions. Guess the only way to tell for sure is when the car is on the lift and I can closely inspect, tap, probe, scrape everything. This is my first MZ5 and I really like it a lot. But if I've got issues that I'm going to be throwing money and time at, then I'll think about selling it and finding a cleaner one from a salt-free area like the Carolinas or Texas or Arizona...
 

HardRightEdg

US 2020 CX-5 Touring AWD Soul Red
So now I have 2 completely divergent opinions. Guess the only way to tell for sure is when the car is on the lift and I can closely inspect, tap, probe, scrape everything.
Right. It's hard to tell from those pictures if there's any spongy or rust-through spots.
 
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FC, FE, Mazda5
Its hard to tell from pictures at the front there, but I don't see any obvious holes, there's still a bit of painted surface on the subframes, and the pinch welds running along the sides are straight, so I'd suspect its mostly surface rust. This will give you an issue with all the small 6mm bolts and studs holding underbody plastics on (prepare for lots of breakage), but larger bolts should be fine.

However, I've found that the real problem area is the back, around the rear wheel wells (especially their leading edge), and the body around there, the rear subframe mounting points, and over the muffler and it's heat shield. That's where the rust on these is almost always at its worst.
 
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2010 Mazda 5 Sport
Yes, you need to go poking and poke in the corners and not just where you can see.

This looks driveable for no more than 3 more years in the rust belt.

My son has a rust free 2010 Mazda 5 since we are from NC. He's going to college in the land of the salted snow so I will be getting the Mazda5 Fluid Filmed twice a year. Dunno if that would help your car as the rust has set in fairly substantially.
 
Its hard to tell from pictures at the front there, but I don't see any obvious holes, there's still a bit of painted surface on the subframes, and the pinch welds running along the sides are straight, so I'd suspect its mostly surface rust. This will give you an issue with all the small 6mm bolts and studs holding underbody plastics on (prepare for lots of breakage), but larger bolts should be fine.

However, I've found that the real problem area is the back, around the rear wheel wells (especially their leading edge), and the body around there, the rear subframe mounting points, and over the muffler and it's heat shield. That's where the rust on these is almost always at its worst.
Thanks!!!
 
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2012 Mazda5 Touring; 2016 Mazda3 Sport
negusm: By "Fluid Flim," do you mean the lanolin based stuff in the gray spray can? I have some of that I bought when I couldn't find Boeshield to try to keep my new brake rotors from rusting on permanently like the originals did. Never occurred to me to try just spraying it all over the place.

Also: What do you mean by, "driveable for no more than 3 years"?

OP: I've been severely disappointed with the rust under our '12. In my subjective opinion it's been showing uglier surface rust for its age than our '03 Cavalier that got traded when the front subframe rusted through when it was otherwise still very nice. Since our Mazda dealer said they didn't do any kind of rust treatment, we've ended up just driving the thing and trying to remember to get a car wash (with undercarriage blast) from time to time.
 
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2010 Mazda 5 Sport
If you drive that car like it is for 3 winters in the salt...I'm betting it's toast.

Fluid film is like what you have but not the same. It is a gooey sort of undercoating that sprays on and sticks like a grease.

Your stuff may be fine too but you need a wand applicator to get it in the hard to reach areas.
 
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18 Mazda CX5 AW
negusm: By "Fluid Flim," do you mean the lanolin based stuff in the gray spray can? I have some of that I bought when I couldn't find Boeshield to try to keep my new brake rotors from rusting on permanently like the originals did. Never occurred to me to try just spraying it all over the place.

Also: What do you mean by, "driveable for no more than 3 years"?

OP: I've been severely disappointed with the rust under our '12. In my subjective opinion it's been showing uglier surface rust for its age than our '03 Cavalier that got traded when the front subframe rusted through when it was otherwise still very nice. Since our Mazda dealer said they didn't do any kind of rust treatment, we've ended up just driving the thing and trying to remember to get a car wash (with undercarriage blast) from time to time.
1st thing is take a heavy screwdriver and see if you can poke holes in the frame, near any spring supports, and the rockers. If the screwdriver goes through you have big problems. You definitely need to spray the whole undercarriage with rust converter ...wait for that to dry for two or more days then coat that whole thing with fluid film. Or find a good local mechanic to do the above. Good 🤞.

You really should convert any rust before you fluid film it.
 
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2015 Mazda 5 Sport
Check the project farm video on YouTube on different brands of rust converter benchmark. Plus fluid film I estimated $300/yr. I also live in rust belt but not sure how long I would keep the car (2015 model). Also fluid film doesn't cover high temp equip like the outside of catalic converter and exhaust pipes right?
 
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18 Mazda CX5 AW
Check the project farm video on YouTube on different brands of rust converter benchmark. Plus fluid film I estimated $300/yr. I also live in rust belt but not sure how long I would keep the car (2015 model). Also fluid film doesn't cover high temp equip like the outside of catalic converter and exhaust pipes right?
There's mixed reviews on rust converter.
I used Rust-Oleum Rusty metal primer spray can for light surface rust areas.
Luckily mine ( 2018 cx5) was only light rust. Wish had watched videos first.

But there are some youtube videos which tested rust converters found the high phosphoric acid converters that are paintbrush on work best. Check vids for products. "Repair geek" video results:
1. Rust Kutter paint on
2. Corroseal paint on
3. VHT spray on
All others failed testing... See video

Of course Coke and Pepsi have phosphorous acid so guess you theoretically could make some cola gel and maybe paint that on?? Not sure how well would work. Although I was able to easily remove rust from alloy wheels with just Coke & aluminum foil, not sure if best solution for rusted frame.

Also don't spray fluid film on cats, exhaust, etc as will burn off and don't spray on shocks /strut assemblys so you can see if they leak/fail. Avoid spraying rubber, boots, etc.

Only spray the underside that's exposed ( Mazda has covers on alot), really spray the rockers, the frame around the strut/shock assemblys, wheel wells not covered by Mazda covers, etc. Don't forget to spray fluid film inside the frame holes, bolt holes, pass-thru holes, etc. Anywhere there's a hole, get some FF in there. If unsure, watch some videos on undercoating car/suv with fluid film. "Repairgeek" has good YouTube video on fluid film. Don't forget to wear your PPE respirator/mask.

Unless you want to remove all the Mazda covers and spray the whole underside ?

Was going to wait and check the car next year and if starts rusting under the Mazda covers then may start fluid film the whole thing but for now seems overkill.

Also is $300 to get it done elsewhere? $300 seems extremely high for DIY and seems high to have done at a shoppe. Only cost me approx $60 to $80 to fluid film it (uncovered areas only as the 2018 has alot of underside panel covers). Should only cost about $150 to $180 to have done by a mechanic, maybe even less. (Assuming 1 hour labor and bulk material costs). Fluid film once per year would be ideal but even once every two years would still be beneficial.

Keep in mind, mechanic can throw on high lift and spray on quickly with bulk fluid film so shouldn't take them more than 1/2 hour to 1 hour labor plus material cost. Imo, really shouldn't cost more than $150 - $180 to coat whole underside (without covers). To save $$, you could take the covers off before take in to the shoppe to get sprayed. Why have them charge $60 or $80 hr just to screw off panel covers? Also either DIY or find an indie...Don't pay dealership $150 labor costs to do something this simple...you'll end up paying dealer $1000 for a $200 job.

If you keep the car it's worth it to FF. If not, the FF treatment will at least make vehicle more presentable/ easier to sell an un-rusted frame.

When buying a used car, I looked under and passed on any car with rusted frame.

Lastly, don't go through auto car wash during winter months..it will wash the FluidFilm off the undercarriage and leave it vulnerable to the salted roads. If you must wash your car in winter, hand wash the body or use car wash stalls with wands to do body only.

You have pics of your 2015 frame? At 7 years, it's probably just starting to look bad as any factory coating has to be wore off by now. How bad is the 2015 ?
 
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