What happened to......catalyst heaters

[V8forweekends]

I know I didn't make this up. Back in the day, Saab 9-5s and BMW 5 series (at least) had a device in the HVAC that retained heat for a few days to enable quicker defrosting on icy days.

What happened to 'em? Did they just quietly stop doing them? Were they superseded by PTC or diesel aux heaters?

[jon-]

Retained heat for days? Were they powered by a small section of the sun?

The laws of thermodynamics are interesting

[Spare tyre]

guess batteries have got better so just rely them to provide electric warmth

[TheEnd]

Catalyst heaters were different, and quite rare too, they were electric heaters for the cat, but it was quickly realised that there were other ways like air injection and moving the cats closer to the engine were cheaper.

The other system was residual heat, and I know the E39 BMW could be specced with it, it was generally a very well lagged tank that kept the coolant warm.
A fairly smart idea, and I wonder if it is still about, but doesn't get mentioned as much.

[jon-]

TheEnd said:

Catalyst heaters were different, and quite rare too, they were electric heaters for the cat, but it was quickly realised that there were other ways like air injection and moving the cats closer to the engine were cheaper.

The other system was residual heat, and I know the E39 BMW could be specced with it, it was generally a very well lagged tank that kept the coolant warm.
A fairly smart idea, and I wonder if it is still about, but doesn't get mentioned as much.

Could this be similar to the "Rest" function on modern BMWs? Uses residual coolant heat when the engine is off, only lasts about 30 minutes though.

[TheEnd]

I think that feature is just an electric waterpump that keeps the still-warm coolant passing through the heater matrix so the blower will remain hot for a while (and then the car will probably refuse to start unless jumped...)

[Motorrad]

V8forweekends said:

I know I didn't make this up. Back in the day, Saab 9-5s and BMW 5 series (at least) had a device in the HVAC that retained heat for a few days to enable quicker defrosting on icy days.

What happened to 'em? Did they just quietly stop doing them? Were they superseded by PTC or diesel aux heaters?

My E39 diesel has an auxiliary webasto diesel powered heater that can be used to warm the cabin before the car starts. Perhaps you're confused with that because there is no way heat can be 'retained' as you describe.

[s p a c e m a n]

Yeah, it was called the 'rest' system on the button on my e39. It circulated the water with an electric pump in the bottom of the radiator that when broken blocked the system up, made the car overheat and exploded the radiator.

Or did that just happen to me?

[otolith]

Some cars (including some Saabs and BMWs) had an auxiliary heater, are you thinking of that?

[Impasse]

Land Rover will supply you with a car with an under bonnet auxiliary heater.

[TheEnd]

I've just checked, the official BMW name was "Latent heat accumulator"

[V8forweekends]

Motorrad said:

My E39 diesel has an auxiliary webasto diesel powered heater that can be used to warm the cabin before the car starts. Perhaps you're confused with that because there is no way heat can be 'retained' as you describe.

OK not retained for days (hazy memories) but, no, not the Webasto - I know what that is from having one fitted to my X350 Jag TDVi and ex's Disco3

ETA - see post above