Another thread here got me wondering about this. I understand why they are there - to warn us of overtemperature. But my quastion is "why" were they put on Ferraris to begin with. What I mean is I don't recall seeing these things on other cars then. Ferrari made them very prominent yet most everything else I recall never had any big concern with pointing out a particular problem with them to be on the lookout for. I remember reading in an owner's manual something about being careful parking over dry leaves/grass etc. but that was about it. Nothing else. No big red billboard on the dash that lit up. Or did all cars have some cat warning system tied into a catch all "check engine" idiot light and I just never knew it? Ferrari had no such "check engine" light on a 308 so they had to add their own - and this was it. Was it simply because the cats were added later to the car meaning it was not really designed for it to begin with and therefore they were prone to run a little hotter? But if that were the case, wouldn't that apply to everything in production before and after the cat requirement? Was it because leaded gas was sitting next to unleaded at the pumps still and folks had a tendancy to "modify" their fill opening and go for the less expensive leaded which affected the cats? Just wondering
My old 77 Lancia has one and some old Fiats too. Now why you need to know if cat is overheating, I don't know, new cars don't have it.
To reduce the risk of fire. When excessive amounts of unturned fuel finds its way into a converter rhe thing will glow cherry red. Doesn't take much to start a fire at that point as plenty of unfortunate owners can attest. Which is why they're still an excellent idea to this day on cars with functioning converters. And yes, they were fitted to other marques.
I said marques as in fine cars, not appliances. Most, if not all, Italian cars of the period had them. I'm not a P-car guy but I think some of them had SDLs as well, and I expect there are others I'm forgetting.
I like having them. Catching a problem early on a Ferrari is quite the money saver. Other cars too, but not nearly as much $$$$$.
I guess I should add that in those days running a car at WOT for long periods (such as on a top speed run) would often overheat the catalyst(s), so the SDLs were actually well-named. BTW, just because EMS technology has improved and we no longer need SDLs doesn't mean that converters don't still increase the risk of fire. You sure don't want them on a track car because an off into even moderately high grass can easily start a fire.
We are fortunate that our cars have one converter per bank. If one bank's ignition shuts down on cars on which the converter is shared between both sides of the engine, the raw fuel from the dead bank will light the catalyst off in a big way. And since those cars usually have their exhaust system packaged in very close proximity to the bodywork and other components, the potential for damage$$$ is much higher than on our cars.
Just a guess here but I think anything that had either carbs or mechanical fuel injection had some form of cat overheat warning. With EFI came an ECU and a check engine light.
In the late '70s, early '80s, single phase cats were added by mandate, not because they were ready for prime time. The "slow down" light is a cat over-temperature indicator. In the 3x8, the "Cat computer" is supposed to blink the light above one temp, and turn it on solid after another. Many of the Cat computers and temp probes have gone south over the decades. A single phase cat simply "burns", in the exhaust, any fuel the engine failed to burn. If you keep your car tuned, there shouldn't be anything for the cat to do. It was added, by dictate, to assure that the car will "break" when it needs a tune-up. The CA version of the Spica Alfas also had the "cat overtemp" light and the warning about not parking over anything flammable. My '79 Spica Alfa is a 49 states edition, with no cat --- and it aced emissions every time, up until states declared it "too old to test". But it also assures that I'll never move to California -- the one state that required a cat in '79 ... even if you didn't need it to keep the exhaust clean. This is why lawyers shouldn't do engineering.
I'd like to clear up a few things in this post, if I may. Converters were not mandated. Limits on emissions were prescribed and manufacturers were left to figure out how to meet those limits. Catalytic converters were one aspect of the solution, air pumps and the further development of mechanical fuel injection and the introduction of electronic fuel injection were others. Not all engines used the same solution. The original cats were "two way" cats, meaning they controlled CO and HC emissions. Three way cats were later developed that also were able to control NOx emissions and those are still in use today. Modern systems often include smaller "pre-cats" upstream of the main cats that come up to working temperature faster and help reduce cold start emissions until the main cat has reached working temperature. Some early cat-equipped cars had the over-temperature idiot lights. Since the cars didn't have any more sophisticated monitoring systems, it was better than nothing. The early cars that used cats sometimes had malfunctions that sent an overly rich exhaust through the cat which caused a few cat failures and a few fires. Thus, the "do not park over dry grass or leaves" warnings in the owner's manuals... Cars that were maintained by the manufacturers instructions generally never got to the point where a cat failure was likely, unless some component broke or the owner drove the car like an idiot. There was no "breaking" to indicate the need for a tune-up. Modern EFI systems typically monitor cat performance by keeping an eye on misfires and how much correction is needed to the stored values for fuel and ignition parameters in the computer maps. Any deviation outside of a certain range triggers the check engine light to illuminate. Given how many people continue to drive with one of those lights on, having the over-temp idiot lights would still be a good idea. Cats do still overheat and fires do happen. My oldest son has been through several incidents recently with one of his Ducatis. If anybody is looking for parts for one of these systems, I have some listed for sale in the classifieds. They were originally for an early TR but I think Ferrari used some of the parts on other models in that era. JR
70's vintage BMW's had a thermo-reactor light, same thing but funny wording. Had a girlfriend at the time who thought the car had a nuclear reactor in it �� The light is triggered by the thermocouple reading via the cat ecu. Early fire warning system.
They were called thermal reactors on the Mondial 8 as well. And its thermocouple often chaffed on the lower heat shield.
My 82 Alfa Spider does not have a cat temp light. I thought it did but it doesn't. Neither does my 80 Scirocco.
For what it's worth, my old '76 Fiat X1/9 had one of these warning lights. Keep in mind, catalytic converters were pretty new tech at the time. At least for consumer automotive applications.
Thermal reactors are not the same thing as 2 way catalytic converters. Although they both attempt to oxidize various gases in the exhaust stream, thermal reactors generally replaced the traditional exhaust manifolds and cats were a little more sophisticated in operation and always downstream of the manifolds. Porsche used thermal reactors from about 1975 through 1977 on the 911 engines and the excessive heat associated with them essentially ruined those engines in short order. Water cooled engines fared a little better but they were a terrible solution to cleaning up the exhaust. JR
