Solving the Fume Problem in a 280Z

[Zhorse]

The fume problem, as most of you know, has to do with the Z car’s aerodynamics. The simplest explanation I’ve read is that a bubble of air gets trapped around the rear end of the car at speed. Since the exhaust exits back there, its fumes get trapped in this bubble. If there are ANY openings in the rear of the car, they will allow this fume-laden air into the cabin.

My efforts on solving this problem were based on a lot of information gathered from the online forums. Since I couldn’t find any one, definitive explanation on this subject, I gathered these all tips into a folder and addressed them, one by one. I also discovered a few things that I did not find in the forums/archives.

Two more things: 1) this article is based on what I found in my daily-driver ‘76 280Z coupe, and confirmed with a ‘75 parts car and ‘77 coupe I had at the time. I am reasonably sure most of the following information will apply to 240 and 260 coupes, as well, but no guarantees. I don’t know if any of it will apply to 2+2 cars since I have no experience with them. I don’t even know if the 2+2s suffer from this problem. 2) Everything you’re about to read here assumes a solid, rust-free car. All bets are off if you Z looks like rusty Swiss cheese.

Okay, it’s easiest to break this up into seven separate areas you need to check: Firewall, exhaust system, shifter boots, rear quarters, rear deck, taillight panel and rear hatch.

FIREWALL — I do not believe that I had any fumes coming through my firewall. I base this mostly on the fact that I don’t smell any exhaust or gas fumes when the hood is open and the motor is running. If you do, then take particular care to seal your firewall.

The basic drill here is to replace or reseal any hoses, wire bundles or grommets where they go through the firewall. The most obvious of these is the accordion-like throttle rod boot beside your master vac. This item is rotted away on just about every old Z car I’ve ever seen in the junkyard. It’s only a few bucks for a new one and a good investment. You can also buy replacement original or aftermarket seals for everything else under the hood while you’re at it, but if you’re a low-bucks Z owner like me, silicone or another sealant of choice works just as good. I replaced the throttle boot with new and siliconed everything else going through the firewall.

EXHAUST — Pretty obvious: If you have exhaust leaks, fix them. In

particular, check exhaust pipe/manifold gasket and all pipe clamps or welds at resonator/catalytic converter and of course muffler. You can tell leaks either by black sooty residue or by putting your hands around (NOT on) the exhaust with the car running and feel air puffing out.

SHIFTER BOOT — The main one of these you have to be concerned with is the big rubber one under the leather-like one you see inside the car. To access the rubber one, you have to take the center console off. Then you can’t miss it: it’s big, rubber, and it seals the shifter hole in the tranny tunnel from outside air. It’s not a particularly cheap item (about $40) but well worth the $$ and easy to install. While you’re at it, buy the small ‘inner’ shifter seal that seals the top of the tranny from road dirt, too.

REAR QUARTER(S) — Now we’re getting somewhere. In my cars, this was a MAJOR source of fumes, especially on the driver’s side (because the exhaust system is on that side). Upon removal of the plastic interior rear trim on the driver’s side, I found one big and one small air leak. Both are under the car. To see them, get under the car and look up at the panel outboard of the muffler. (You don’t need to jack it up.) You will see two holes, one big one small. The smaller of the two at the bottom is, I think, the drain for the power antenna — which not very many Zs have anymore. On my car(s), the little plastic piece in this hole was all hardened and dangling. Replace or plug with silicon.

The other hole is harder to see because it’s higher up. I have no idea what this 2-inch hole is/was supposed to be for. At any rate, Datsun stuck a rubber plug in this whole at the factory, and on all three of my 280s — it had rotted out in the middle. Since it was right beside the muffler, this is a literal black hole for fumes. Again, replace or silicon it closed. BTW, I found these holes by putting a halogen light under the car, shining straight up, in a darkened garage. Then stuck my head inside the rear quarter. Wherever you see light coming in, thats an air leak. So keep sealing until you see no light.

On the passenger-side quarter, I did not find any leaks or rot in my gas tank vent hoses. If you do, then replace them. (I think a gasoline smell, rather than exhaust, would be more indicative of a leak here.)

REAR DECK — This is the part of the car under the rear hatch, where the spare stows. I do not believe I had any serious fume leakage in this area, simply because there aren’t that many holes. However, on my car the grommets around where the hoses to the vent tank went through the rear deck were rotted, so I squooshed more silicone around them to make them airtight again.

TAILLIGHTS AND REAR PANEL — Per suggestions on several forums, I bought new taillight gaskets and went through the laborious process of removing my taillights to put them in. However, once my light fixtures were out (there are lots of little nuts so be patient and careful), I found that original foam rubber gaskets, though old and funky looking, did not have any breaks and did not appear to be leaking. If yours are, of course replace them. HOWEVER, I did have a couple of rotted rubber thingies on the actual bulb fittings. These are the thin rubber seal things through which the wires pass into the bulb bases. When rotted, these seals DO leak air (blow through one without the bulb if you don’t believe me). If these are rotted, or the spongy gaskets on the bulb fittings where they quarter-turn into the taillight housings are gone or rotted, you can get fumes sucking in there. ALSO, the rear taillight lenses themselves leak air. They are not totally sealed all the way around, but have small rectangular openings — probably drains — at the bottom of each lens. I did not seal these on my car, but if I still had fumes after all I did do, I’d try that next. One more thing on the rear lights: the lenses are mounted in some kind of white plastic stuff that was apparently soft at the factory. On my car, this was still pretty soft — kind of like an Abba Zabba candybar — and seemed to be well sealed. But on my parts car, the white stuff was hard and the lenses were loose enough to just pop out by hand. If yours are this way, I would reseal them with silicone (except for the drain hole) and reinstall.

REAR HATCH — This, in my opinion, was the main fume culprit on my car and, I suspect, most first-gen Z cars. One of the early band-aids I tried was a new rubber seal between the hatch and body. If anything, this seemed to make the fume prob worse. WTF?? So I got to looking at the hatch itself and discovered four holes in the lower edge of it (look under the rear lip when it’s open). Two are large rubber drain plugs, two are simply small half-inch holes. The driver’s side drain plug on my car was rotted almost away. I resealed it, and the other big one. I left the smaller drain holes open because, at this point, I had a sudden flash on the biggest culprit in this whole gory scenario, at least for me: the trim panel on the lower rear hatch. This is the vinyl-covered panel about 6 inches by two feet that is screwed and/or plastic-riveted to the underside of the hatch, right below the hatch release button. Please note that when the hatch is closed, this panel is INSIDE the car. I am convinced that my major fume ingress was through or past this panel — thanks to online forums for this tip.

What I did, and what you should do, is remove this panel and put a piece of visine plastic between it and the hatch before reattaching. You know, clear plastic like is under your interior door panels. A vapor barrier, basically. You can do this with that 3-M sticky stuff like is on the doors, or silicon. I was so gonzo by his time that I siliconed the living crap out of the opening, the plastic, and the panel — then ran a final bead around the panel when it was reattached. In short, I made a big mess that needs to be cleaned up, but that frickin panel is SEALED.

BTW, after you do this, leave the hatch open if you can for about 24 hours to allow the silicone fumes to dissipate.

Anyway, that’s how I did it, and it worked. I don’t get any perceptible fumes in the car at any speed now, even with the window open. (Well, except at slow-speed decel for some reason.) My wife will even ride with me again, though I haven’t decided if that’s a good thing or bad one.

Good luck!

— ZHorse (John Riise, 1976 280Z)

Photo captions:

Photo 1 — There four drain holes — two large and two small — under the lower rear hatch. This hatch doubtless still gets fumes inside, but they are stopped from entering the car by the well-sealed interior panel and a good rear hatch seal.

Photo 3 — Arrows show the two holes on the LH inner quarter panel of 280Zs. Note the larger of the two has a rotted-out center. Being right next to the muffler (removed in this picture), this hole would suck fumes big time.

Photo 4 — This photo shows the drain hole arrangement in the taillight lens of a 280Z. If your bulb wire seals are funky, you can actually get fumes coming in here and sucking through the old wire seals.

Photo 5 — Another shot of the drain hole on the rear lens. All three lenses have these. This photo also kind of shows the whitish, semi-soft lens mounting stuff.

Photo 6 — Here’s what I’m talking about with the bulb wire seals. The arrow is pointing to, in this case, a damaged seal. This will leak air. Also check the foam gaskets where these fittings quarter-turn into the taillight housings.

[280zgod]

man you are awesome i have that problem i keep wondering where the fumes are coming from. i bought a new shifter gromet and had my exhaust completed welded together and checked the firewall. it must be one of those others. thanks for the advice on this subject im definitely going to find the culprit now that i have some idea on this thank you thank you. ~Jerrod

[Hrududu]

wow. Thanks for putting the time into this. I really am glad you did so now i can fix this problem.

[TomoHawk]

Don't forget to check the area behind the rear wheels. the plastic rear 1/4 pieces are open to the air, believe it or not, and these pieces are supposed to keep the water and fumes out of the car. Mine ewere MUDDY on the back when I took them out, andthere were a few leaves in there.

One overs the evaporation tank, and the other one covers the antenna.

[EScanlon]

Tomo:

The fender support at the bottom of the quarter panel has apparently rusted away on yours. This is not an unusual problem for vehicles in the rust belt. Water / moisture gets trapped behind the plastic panels and runs down to the support. There it pools and accelerates the rust through.

Look at the sheet metal that's the "outside" of the car from the inside, there should be a line where the support was welded to. That's how you can confirm that there WAS a support panel.

E

[TomoHawk]

Tomo:

The fender support at the bottom of the quarter panel has apparently rusted away on yours. This is not an unusual problem for vehicles in the rust belt.

Since when is Florida in the rust belt?? I will have to go look some more to see what happened.

thx

[beandip]

Tommo the last time I looked Flordia was pritty much surrounded by salt water. Beach cars suffer the same as those driven on salted roads . And you have been driving this Z for how many years ?

[sblake01]

Tomo, I just checked my 78 with a flashlight and there are no areas behind the wheel wells that are 'open to the air'. There is a rubber grommet on one side where the antenna drain comes through and two rubber grommets on the other side where the gas filler and the hose to the expansion tank go. They all seal well as I replaced the two smaller ones in 1999. I checked underneath and inside, no areas that are open to the air.

[dogma420]

Another great place to look to seal up holes are checkout all the drain holes from the rear seat brackets on back all the way to the taillights. When getting rid of my fumes, I did most of what Zhorse recommends, but I was still getting some fumes smell!

I noticed that through the 'frame rails' on each side of the wheel well, there is a hole on each side...I sealed those up, and made sure the drain plugs at the bottom of the spare tire well and drains just behind the seat brackets were all sealed up. No more fumes!

[dogma420]

Another great place to look to seal up holes are checkout all the drain holes from the rear seat brackets on back all the way to the taillights. When getting rid of my fumes, I did most of what Zhorse recommends, but I was still getting some fumes smell!

I noticed that through the 'frame rails' on each side of the wheel well, there is a hole on each side...I sealed those up, and made sure the drain plugs at the bottom of the spare tire well and drains just behind the seat brackets were all sealed up. No more fumes!