How to protect your new subframe from rust?

[Carolyn]

I'm going to conduct an experiment.  My subframe has been sealed at the corners for over a year.  I'm going to drill a hole in the appropriate spot (maybe two (to be sure) and see what comes out.
I'll report my findings

Ok.  First, this is all in relation to a Pre Facelift subframe.  One must bear in mind that they have different geometries.

I happen to have one that we cut open while experimenting with sub-frames for the supercharger conversion.  So I examined that one.  It is rusted in the usual place, and you can see the rust from the inside.  It turns out that the pre-facelift has a bung right at the premium rust spot:



This picture is of the INSIDE of the subframe. Edit:  There are two factory done drain holes.  You can see one (the smaller hole in this picture).  They aren't at the lowest point and don't seem to help...

I then took that bung out of my daily driver that has had the top corners sealed for 18 months.  It is a JDM import that has only been exposed to our weather since late 2007, and then had relatively little use until I got it.  To my knowledge, and looking at the history that came with the car, this is the original subframe. It is bone dry inside and (by sticking my little finger in and feeling around), there is no rust at the low spot.  We rocked the car around.  Nothing came out.  I then took the bung out from the top, just above the classic rusting place and introduced my endoscope.   It's clean, slightly discoloured but no rust.  I shall take the opportunity to shoot a little waxoil in there while the bungs are out, and then they are going back.

[lamcote]

I have just had a close look at the new facelift subframe I bought a few months ago, not yet fitted.

It has drain holes in it which do appear to be at, or very close to, the two lowest points. As it is raining I haven't yet checked whether the original subframe has these, but I will have a look at some point. It would be interesting if these turned out to be a revised design feature as it may mean the latest subframes should last longer.... Or not!

I do wonder whether wrapping the exhaust where it is closest to the subframe might help to reduce the problem also?

[Carolyn]

My exhaust is wrapped.  Both my cars, and the extra subframe I cut open have drain holes, so I suspect they all have them (given your info on the Facelift ones).  My only additional thought is that the presence of an electrolyte greatly accelerates the rusting process.  What was my car not exposed to for much of its life?  Salt.

As the cars all have drain holes, and as the subframes seem to rust anyway, perhaps it's about salt build-up?

[Bodgeroo]

Both my new subframe and old (both post facelift) have exactly the same holes. Interesting though @carolyn my rotten subframe does have signs of salt inside.

[Carolyn]

So, sealing the top corners would seem to make sense as that's where real road filth can get in.  The drain holes should allow for adequate ventilation.  Anyway, that's my theory so far - and now we seem to be accumulating evidence, rather than opinion.

[Bodgeroo]

I think the presence of salt was due to the gaping hole in mine  s:D s:D

[lamcote]

Yes, this is very helpful. Does the Dynax treatment protect against salt?

As you say Carolyn, if the main culprit is salt, blocking the holes will presumably help because the only way that gets in is from salty water splashing up from the road. The issue raised about water vapour seeping through small gaps and becoming trapped would be less of a concern than the salt ingress.

[lamcote]

Do we know if there are similar rusting problems in countries where no salt is used?

[Carolyn]

It might seem counter-intuitive, but if treating a subframe on the car, it might be best to pull the bungs and wash it out with clean fresh water, let it dry, rust-proof it (treatment of your choice), put the bungs back and seal the corners?
Well mine is from Japan. It rains but they don't salt the roads. It's a 2001 Pre Facelift and it's OK.

[Carolyn]

Do we know if there are similar rusting problems in countries where no salt is used?

Good point.  I've put a request for info on Spyderchat.

[lamcote]

That would be good intelligence.

In summary it seems to me that if we are protecting against just water you want holes and ventilation.

If we are protecting against salt you want everything sealed up tight.

The trouble is, choose the wrong one and you could actually be accentuating the problem, so the more information the better.

[Carolyn]

I'm not sure it's quite so black and white.  I like the drain hole idea... seems to me the road muck will mostly get in via the holes at the top corners (probably on the nearside where all the splash from the gutter goes)

[lamcote]

Having looked at some old threads I think Nylon coating is looking like a good idea.

[tricky1138]

I was looking at POR15 for the outside and Dinitrol for the inside, but now reading this I might look at other options.

[cptspaulding]

I was looking at POR15 for the outside and Dinitrol for the inside, but now reading this I might look at other options.

"WARNING: THIS PRODUCT CONTAINS CHEMICALS KNOWN TO THE STATE OF CALIFORNIA TO CAUSE CANCER, BIRTH DEFECTS OR OTHER REPRODUCTIVE HARM."

From the POR15 website. Careful with that stuff, Trick.

[Bernie]

Having looked at some old threads I think Nylon coating is looking like a good idea.

FGRob had the one on mine nylon coated so would suggest same as he always did a top job, even made up a heat shield where the exhaust crosses it  :-) :-) :-)

[lamcote]

Do you have any pics of the heatshield I had wondered about doing that too?

Thanks

[Bernie]

Do you have any pics of the heatshield I had wondered about doing that too?

Thanks

I'll take a few tomorrow

[lamcote]

Great thanks.

[JoeCool]

Out of interest, that metal heat shield that stands up from the cross member: Any idea what it protects from what? My intake is re-located now, and I'm not sure that heat shield has any utility.

[Ardent]

I would tend to agree.
I thought there to act a a barrier between intake pipe and zorst manifold.
If intake pipe in now located elsewhere..

[Essex2Visuvesi]

I was looking at POR15 for the outside and Dinitrol for the inside, but now reading this I might look at other options.

"WARNING: THIS PRODUCT CONTAINS CHEMICALS KNOWN TO THE STATE OF CALIFORNIA TO CAUSE CANCER, BIRTH DEFECTS OR OTHER REPRODUCTIVE HARM."

From the POR15 website. Careful with that stuff, Trick.

It's fine we're not in California   s:lol: :lol: s:lol:

[Bodgeroo]

Related question  - now I have all the nuts and bolts off and have started to clean them up - which bolts used the nylon lock nuts? I assume these were used as the cam plate nuts?

[Carolyn]

Not getting anything particularly helpful from Spyderchat (so far) as most of the cars are in the Southwest and they don't rust. It is very 'American' to have a car that is an extra toy for fine weather use, especially in bad weather States.  Looking at Stavros58's 'New Clutch' thread, we've got 06's rusting out and early ones not (sometimes).  I'm thinking the key may be that some cars are stashed for winter and some are daily drivers driven year round. It does appear to relate to winter use as it is just as wet here regardless of season.

[Bernie]

Do you have any pics of the heatshield I had wondered about doing that too?

Thanks

As promised and prior to a clean as the last couple of drive ours weren't in decent weather  s:-( :-( s:-(







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