By on March 17, 2012

A couple of recent Junkyard Find Datsuns (the ’78 510 and ’77 280Z) featured mysterious “FLOOR TEMP” idiot lights on their dashes. Floor temp? Why?
The thing that really put the malaise into the Malaise Era was the inability of the automotive industry to meet US federal and– in the case of cars sold in California— state exhaust-emission regulations without crippling the vehicles (whether this inability was due to Naderite anti-progress bomb-throwers infesting the government or corporate mismanagement and the over-reliance on lobbying to fend off emissions regulations is your subject to debate). While Honda’s CVCC engines managed to beat the tailpipe test without the use of the early, incredibly inefficient catalytic converters, just about everybody else had to bolt a super-restrictive and surface-of-sun-temperature cat onto the exhaust. On low, sporty vehicles that didn’t have a good location for the catalytic converter, an overheating cat could set the car’s interior on fire. Nissan’s solution to this was the FLOOR TEMP indicator light, which used a temperature sensor near the catalytic converter to warn the driver to slow the hell down. We can assume that no Datsun drivers actually read the owner’s manual (as a former technical writer, I know that you can’t get anybody to RTFM), and so the FLOOR TEMP light just confused them.
The Italians took a different approach. Fiats, Ferraris, and (I’m pretty sure) Alfa Romeos of the late 1970s got this lovely and equally confusing “SLOW DOWN” idiot light to warn drivers of overheating catalytic converters; at least this light gave the driver some idea of the remedy for the problem. Some Fiats and British Leyland cars got a similarly cryptic (yet technically more accurate) “CATALYST” idiot light. Perhaps a really big idiot light reading “CATALYTIC CONVERTER OVERHEATING — SLOW YOUR ASS DOWN OR PERISH IN FLAMES!” would have been best.

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47 Comments on “What’s the Deal With those FLOOR TEMP Warning Lights in Malaise Era Datsuns?...”

  • avatar

    Looking at those old dash boards, there is one thing I definitely don’t miss about those old cars: Exposed screws heads on the interior in plain sight.

    • 0 avatar

      I noticed that too – but had the except opposite reaction!

      Exposed screws just screams to me that is car is an easy to work on DIY special. Taking apart much of the dash *almost* looks fun!

      • 0 avatar

        Depends what they threaded into. The older cars had chromed or nickle finished screws that were screwed into sheet metal. The 70’s cars had black oxide, or zinc finished screws threaded into plastic. Guess what happens when you try back out one of those screws from its 20 year old (brittle as glass) plastic home? You can get them out alright, but what’s left of the plastic it threaded into will never hold a fastener again.

      • 0 avatar

        You are right. Cars are (should be) mechanical devices. It’s interesting to see how they are put together. A car has more “soul” if you can look at fasteners / check marks etc and think about the guy who put it together 25/50/100 years ago.

    • 0 avatar

      Peugeot got rid of those exposed screwheads, at least on the 404, somewhere between 1961 and 1965.

      • 0 avatar

        Peugeot 504 – I remember the door panels, top of the dash and rear shelf as well as a lot of the dashboard panels were held on by Velcro in combination with a couple of well placed friction clips.

        I remember wanting a new dashboard top and a couple pieces that had baked and cracked in the sun, but ended up buying an entire interior for less than $250, including seats, carpets, all the panels and even the instrument cluster. It took no more than 30 minutes to strip in down to bare metal.

    • 0 avatar

      I don’t mind the exposed screwheads except when they’re oxidized like the one pictured. How about a nice finish on the screwhead that doesn’t look crummy after a few years?

    • 0 avatar

      Yeah knowing at a glance how to take apart a dash instead of endless probing and breaking of brittle trim and clips was sure terrible. LOL

  • avatar

    Back in the day, I parked my parents’ 1983 Plymouth TC3 (the swoopy version of the Horizon) in a grass parking lot at the Indianapolis Motor Speedway, and I started smelling smoke. I pulled out of the spot and the grass was on fire. This was a small non-high-performance engine, and it wasn’t working hard, but the cat still caught the grass on fire. I’m surprised they even let you park on the grass anymore for public events.

    • 0 avatar

      Had a similar situation with a Crown Vic in tall grass…Turns out if you leave the engine running for more than about 10 minutes you can start a small forest fire. Thankfully grass doesn’t ignite if it’s still green but I did leave behind a nicely sized 4.6L-sized burnt mark.

      • 0 avatar

        There was an episode of Cops in which they were chasing a perp across the golden, grassy fields in summertime, and lost one of their Crown Vics when it set a grass fire around itself.

  • avatar
    Volt 230

    I un-fondly recall driving from L A to Vegas in Aug 1979 in a rental Ford Fairmont with around 39k miles and reading the signs along the way: “Turn off A/C or your car WILL overheat” and seeing a few cars and Rv’s on fire at the side of the road and since this Ford appeared to be in its last legs despite its rather low mileage, I did not want to take a chance with 4 aboard plus a trunk-full of luggage, so the A/C was turned off and we spent about 4 to 5 hrs in a Swedish Sauna on wheels, we’ve come a long. long way, baby!

    • 0 avatar

      Yeah, I remember family road trips in the 1970s that involved sightings of broken-down cars every few hundred yards in hot weather (not to mention the family cars— Fiats in some cases— themselves breaking down). Also the reek of unburnt hydrocarbons on ALL roads, all the time.

    • 0 avatar

      Kinda funny, esp. since the 1950’s, Ford has done their hot-weather testing just outside Vegas!

  • avatar

    I sped my Datsun and lit the floor
    It did not last the flight
    But oh my foes, and ah, my friends
    It cast a lovely light!

  • avatar

    Lovin the “Slow Down” as I was already looking for replacement of Google Search page.

  • avatar

    Some chrysler products also got by for a couple of years without a catalytic converter.

    • 0 avatar

      True – my 1976 Dart Pursuit ex-cop car had factory dual exhausts sans converters.

    • 0 avatar

      Ah, the Electronic Lean Burn system. My mom had a ’78 LeBaron T&C wagon so equipped that I learned to drive on. That 318 was probably about as emission-choked as they got, but to my novice right foot it felt like a rocket sled.

      Oh, and Mom insisted that I polish the ‘wood’ with lemon Pledge. “What d’ya mean it’s not real wood? That’s ridiculous. Quit slacking and get to work!”

  • avatar

    I’ve always known you should not park your cat equipped car over grass, especially TALL grass for that very issue, catching the grass on fire!

    It may still be an issue today though the threat probably isn’t as big now as it used to be with those early catalytic converters.

    I remember the heat from the one in my 78 Ford Fairmont that would rise up as you slowed down, or stopped even and had the window opened, it was pretty bad.

    BTW, where I read about the cat and grass thing was IN an owner’s manual at one point and I think it’s probably still not advised in modern cars in the manual.

    Yes, I DO read the manual and have on my Mazda Protege5.

  • avatar

    If I recall correctly, catalytic converters tended to overheat when the engines ran too rich, effectively overloading the converter’s ability to cleanse the exhaust. So something like a stuck choke (or in rare cases like with the EFI in the 280Z, if it had some glitch) would cause the cat to not only overheat but produce that rotten egg smell.

    My favorite story from back then was from a guy my father worked with. On a family vacation, the heat coming out of the tailpipe melted the wheel on a bicycle hanging on a bumper rack. Not the bike’s tire, but the aluminum WHEEL.

    • 0 avatar

      Fact: 1/3 of the fuel burned is exhausted out the tailpipe as heat (other 1/3 is rejected out thru the cooling system and last 1/3 is turned into mechanical work.)

    • 0 avatar
      Felix Hoenikker

      Excess unburned hydrocarbons caused the overheating in catalytic converters in the 70s, Engines ran richer during hard acceleration leading to higher loading of the converter as the HCs were oxidized to CO2 and H2O. The basic problem was that carbuerators could not maintain a constant air to fuel mixture across the full throttle range. At open throttles there was an increase in HC concentration as well as an increase of exhaust gas flow. This results in a higher higher mass flow of unburned HCs, and therefore a higher heat generation rate in the catalytic converter. The problem was solved with the advent of closed loop fuel injsction and ceramic honehycombs instad of pellets in the converter.

  • avatar

    At sustained hwy speeds, with 5 passengers and luggage, my father’s then new 1976 Gran Torino would slowly roast the fannies of the back seat passengers…

  • avatar
    John Fritz

    Hmmm. The second I saw that warning annunciator I knew what it was for. Showing my age I guess.

    Honestly, I’ve never seen one before. Although I have ridden in a few cars that needed them.

  • avatar

    Around 1976 there was some controversy about the newest local police cars in Delmar, NY having air conditioning. Eventually they justified this extravagance with the catalytic-converter-heating-the-floor bit.

  • avatar

    A friend of mine was returning to college in her Colonnade Regal on NY 17. It was packed with her friends and luggage. Someone smelled smoke, and they discovered the interior carpet was starting to smoulder. Catalytic was the culprit. Back in the day, a lot of people replaced the cat with a straight pipe. Ostensibly this was just for “testing” purposes. I did this with my ’80 Century. Had to replace the cat when NY started cracking down in late ’80s. I always wondered why nobody sold a hollowed look alike cat that would get through inspection.

    • 0 avatar

      Here in Florida, during the late 70s, I remember Western Auto selling a Catalytic Converter case. It looked like a normal cat but was hollow. Lots of warnings about off road use only. But the inspectors only looked to see if you had one installed, they didn’t use a sniffer to check if it was working.

  • avatar

    Instead of the heat sensors and dummy lights, they could have installed GM air conditioners, that way the water could piss out all over the carpet to cool the floor just like the trailblazers do!

  • avatar

    My ’76 Alfetta sedan had the SLOW DOWN light in it. It illuminated exactly once, when I was in a train of cars going 90+ down US 101 – since this was during the 55 mph speed limit it felt like serious motion and I didn’t want to lose the group. It flickered on, I backed my foot off the gas a little, it went out, I put my foot back down. No problem, and the car passed smog without any twiddling or parts changes the next time. Even though it had only 110 hp – just a bit more than a normally-aspirated 320i – it sure was a fun car and I miss it, except for the clutch changes.

  • avatar

    I know some would just remove the converter for all-round improved performance. Wasn’t likely ‘traffic,’ would go looking for it.

    My first reaction was el cheapo split level climate-control. Early vogue in the mid-70’s [Rolls Camargue 1975.] I guess that would be more involved than those blessed Hyundai repeaters in today’s door mirrors.

  • avatar

    2001 360 has a slow down light. A separate ECU references a thermocouple just past the second cats. The ECUs fail, of course. Italians…

  • avatar

    I don’t remember my parent’s 1978 Colt (Lancer) having a floor temp light as a kid, but I do remember the floor or the driveshaft hump getting pretty toasty on trips that involved driving an hour or farther away.

  • avatar

    I recall reading the owners manual of my mother’s ’77 Buick advising against parking off road over grass or leaves because of the risk of fire from the heat of the catalyst, although I never felt any excessive heat on the floor of the vehicle. I do recall hearing that some refineries would not allow automobiles with a catalytic converter to enter certain areas of the plants. I was in the Air Force Reserve in the ’70’s and automobiles with a catalytic converter were not allowed on the flight line because of the heat they created.

    • 0 avatar

      I was getting ready to mention that myself, the owners manuals of all converter equipped cars that I know of warned not to park over leaves or tall grass.
      My Dad bought a new ford wagon in 75 and cut the opening bigger in the fuel filler and started using leaded gas in it, which pretty much rendered the converter ineffective. When it came time to replace the Y pipe after a few years he bought one for a 74 model and removed the converter.
      I remember auto parts stores selling what they advertised as “catalytic converter test pipes.” They bolted in place of the converter, and were advertised for use for ‘checking for a clogged converter.” Yeah right. lol.
      Ford converters were a monolith type, and were less restrictive than the pellet types used by GM and Chrysler. People in places with smog checks like California that modified their late model GM and Mopars for better performance would use the Ford converters.

  • avatar

    RX-7s had an “exhaust overheat” light at least as late as the second generation. Then again, Wankels have higher EGTs than piston engines.

    My RX-8 singed some grass I parked on – it didn’t quite catch on fire, though.

  • avatar

    I always wondered what the “Slow Down” light meant on the Fiat 124 I learned how to drive stick on… I always liked that the “Slow Down” and “Brake Failure” lights were usually on at the same time.

    While Mr. Martin has made his semi-dislike (?) of the 124 known a few times over in his junkyard reports, I’d say it was a great little car to learn something like the “Lemons” spirit in — it was a great little tow car (for a small sailboat), only almost blew up once when a Czech couple helped me jump it and only once lost the rear passenger-side wheel while in motion. I can’t listen to the “Crystal Ship” now without hearing the whine of the Fiat four-banger in the background because of the always-stuck-in-the-Radio Shack-tape-deck cassette. I miss that little car.

    I think I need to track down a “Floor Temp” and/or “Slown Down” light for my current car. Much more fun (or alarming for passengers) than the legal warnings for iDrive.

  • avatar

    A guy was following an Omni or K-car, can’t remember which, at night many years ago and noticed a bright light illuminating the underside of the car. He got the driver to stop and they determined it was the cat. The alternator had failed and it was running on the battery alone. The weakened spark was feeding more fuel to the cat.

  • avatar

    the “golden era of japanese turbo sports cars” (say 1990-2002) all had cat overheat lamps

    but with modern fuels and ecus i don’t think it was really an issue unless the car was tracked

  • avatar

    Ford enriched the mixture in their carbs at idle in an attempt to cool down the cat. The 300cu six I had with an electronic carb has a solenoid for this purpose. I didn’t think it worked in any case.

  • avatar

    I always thought it was running too LEAN that cases the cat to glow. Or the exhaust.

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