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Rusty bolts issue?

29 August 2022
Hi everyone,

I am looking to buy a 92 NSX that is super clean but has a lot of heavily corroded bolts underneath.

My question is, how worried should I be about very rusty bolts underneath the car? I will certainly want to replace all the bolts, but does that mean the aluminum parts in contact with the rusty bolts might be affected too? Also, does this indicate that the car was stored in high humidity, which means there is a risk that there are more rusty bolts throughout the car in areas I can't even see?

Thanks in advance for your help.
Without pictures hard to determine. Likely drove on salty roads one mid winter day...it doesn't take much. Fearing the dark isn't generally very helpful.

Aluminum oxide isn't really a concern as that is a protective coating. Just doesn't look all that great.

Rust is a problem, go ahead, order up new bolts from Honda, and replace away. You do need to use the specially coated bolts from Honda as galvanic corrosion is a thing.
Thanks for the replies. Here are some photos that show the rusty bolts. It's not that bad I guess, maybe about 1/5-1/4 of all the bolts are rusted from what I can tell. I was just worried that it might cause corrosion to the aluminum body, and also indicate a risk that there might be other rusty bolts hidden in areas of the vehicle that I can't see.


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Ok, good to know the rust is normal for North East. I agree it's a good sign the owner used the right oil filter (I've seen other NSXs with the regular Honda oil filter installed which is not a good sign)

I hadn't noticed the oil pan until you mentioned it. It does look a little banged up or scratched actually. I haven't seen this car in person so I can't say for sure though how bad it is though.
Agree it doesn't look bad at all. Have a look at some other 30 year old cars from that area of the US. FWIW, some of those the original bolts would have been "dacro" coated according to the manual (look for a star in the manual), with a light green coating, but can look corroded early. I've noticed however, that replacement OEM bolts no longer seem to have this coating; Was this coating found to be ineffective or too expensive? It's been banned in the EU. I wondered whether an old dacro bolt or a shiny new bolt is a better choice, especially as some folks say you need to replace dacro bolts since the coating is damaged by removal. I asked this same question when mine was "new" 2 years ago:
If you order new bolts, figure out a big order & order from amayama to save some serious $. With a big order from amayama, it's a fun, inexpensive project replacing rusty bolts & brackets. Use a torque wrench.
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Dacro (dacromet) is a trade name. I don't know whether Honda in Japan specifically used Dacro brand corrosion protection. There are other anti corrosion protective coatings.

As I recall, the coated bolts are only used on the body and the service manual calls out all the locations with these special coated bolts. I don't think the coated bolts were used on the suspension parts (correction, I checked the SM and the majority of the nuts and bolts on the suspension and the brakes have the little star indicating corrosion resistant fasteners). All of the bolts that I see in your photos that have rust on them are not body bolts and as such would typically not have corrosion protection on the threads. A lot of the bolts in the photos that are rusted are not body bolts or suspension fasteners and would typically be the special corrosion resistant fasteners that Honda specifies. The surface rust on a lot of those fasteners is probably pretty normal if the car gets exposed to moisture.

In the absence of the correct coated bolt you can use a zinc plated bolt of the correct strength. Zinc and aluminum alloys are very close on the galvanic series chart, slightly overlapping depending on the relative alloys so is unlikely to generate a significant corrosion cell. I believe that dacromet is actually aluminum and zinc in a ceramic carrier of some sort. Whatever you do, do not use a stainless steel bolt in contact with the aluminum body. Probably best to avoid SS on the aluminum suspension components. Stainless has quite a range of alloys and some of the alloys are about as far away from aluminum as you can get on the galvanic series chart.
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Not sure what you mean about a "regular" Honda filter not being a "good sign", assuming you mean the short/long debate. Do a search on prime for this, but any filter specced by Honda is going to be fine. A fancier filter is like a longer ladder than you need - if you need a 6' ladder, a 9' ladder isn't really a big improvement. The changing interval is more important than the filter chosen, so the sign of good maintenance not a long filter; it's a binder full of carefully sorted receipts, showing the correct maintenance schedule has been followed. If you have too much time on your hands:

I would advance that since the long filters have become difficult to source, a long filter could ironically be a sign of infrequent maintenance recently. I get mine from amayama in Japan and a short filter is not a sign that the car has not been well cared for.

Best wishes on your NSX quest. You won't be disappointed.
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Your pictures are typical for a NSX that has been used in a humid and/or salt water environment. It's also common for NSXs that are driven on roads where salt is used to melt snow. Even dry roads in winter have salt dust that collects on the bolts and corrodes the steel when it gets wet (from a car wash or rain). This is totally normal. Replacing the bolts is time consuming, but not hard or expensive. Use a torque wrench.

The Honda Genuine oil filters are the preferred filter for this car. Most of the NSX expert techs around the world choose to use them. Aftermarket filters are just an exercise in marketing hyperbole and may not filter "better" than the OEM. Thus, to me, using a OEM filter is not a not a sign of poor maintenance. To the contrary, it's likely the car was serviced by a tech with NSX experience.

Th potential deformation of the oil pan is, however, a potentially serous issue. I would do an oil pressure check to make sure that the pickup isn't obstructed. This happened to @MotorMouth93.
Thanks for all the advice. The VIN is JH4NA1154NT000865 in case you want to look up the history.

To clarify my oil filter comment, I was just referring to the fact that I've seen other NSXs with the regular more narrow OEM oil filter installed, which I was told by my mechanic is bad practice. I agree this car looks like it is using the right OEM filter for the NSX (wider one), so that is a good sign.

I am concerned about the oil pan now though. I had the seller send me a video of a cold startup and there were no engine lights on. I will see if they are willing to do an oil pressure check.
No oil pressure light on at start up is definitely non - definitive. It only take about 5-7 psi of oil pressure to cause the light to go out. As MotorMouth93 notes, even an actual oil pressure reading at idle is not a definitive indication of whether there is a problem.

The reenforcing ribs on the oil pan go in to the oil pan cavity. This makes it very easy to check the pan for flatness by just laying a metal straight edge (ruler or the like) along the bottom of the pan to check for deformation. Get the owner to take two photos, one with the straight edge aligned along the back - forward axis of the car and the other along the transverse axis. Any 'daylight between the straight edge and the pan surface indicates a dent / deformation.

I am thinking the appearance of the dent might just be the way some dirt / dust has been distributed along the bottom of the pan.
If I ever decide to "go country" my stage name will be

Rusty Bolts..

or maybe in the silver sneakers adult film industry