OT: Why do cars have Tachometers?

I think they are a 'drivers thing'. You can also 'manage what you can measure' and whilst I would agree that most people today have no use for them (not only wouldn't they know what they were but also what they meant), they can be handy on older stuff to aid with diagnostics.

Like, my Honda CB250 has a small flat spot in the carburation when just coming off choke that comes in at a fairly specific RPM. If I was to attempt to remedy the fault, I wouldn't know it I had done so or just moved it up or down the rev band a bit without a rev counter.

That would bother me.

That doesn't sound very intuitive. ;-)

The thing is, with no gauge there is no advanced warning of that is there?

And not uncommon amongst the general public I imagine?

I really think there should be 'worldliness' classes at school, the sort of thing you would learn from a 'How it works' type book. A bit of everything about the world we all live in, from basic geology, materials, chemistry, electricity / electronics, food production, mechanics and energy etc. I know you might get some (and more) of any of that on specific courses, but often to a much greater / specific depth and that would be far deeper than most people would ever need or be able to really understand.

Hehe.

I think it's about the same here, generally doing them because it was sensible to do 'while we are there'. I think the only one that has ever worn out in my possession is this Meriva that was given to my by Mum when Dad died a while back and had spent lots of it's life in traffic.

I think it going high or low under those circumstances is a function of where and now it's mounted. eg, If the actual temperate probe is insulated from it's mount it can go low, even when the surrounding metal is pretty hot.

I think those engines were quite 'robust' (boat anchors <g>) and I know the 2L was a 'safe' engine as I had a cambelt go with no issues (and it was back on the road within the hour).

The only other thing that ever happened with that engine over the

They were all simpler times when you had to set the tickover RPM to be able to not stall when you turned the headlights on. ;-)

Now you can creep up a hill in traffic without touching the accelerator at all. ;-)

Cheers, T i m

:)

I'll try the imagining bit... Am I allowed to picture her as being hot and wearing an appropriately short skirt? If not, I'll pass.

It is. You ensure the engine/box are at temperature, select the sports+ driving mode, press brake very hard and hold with left foot, gear selector to sports/manual, floor throttle past kickdown, when the light comes on the dash release brake and all hell breaks loose as you accelerate like stink.

Thunderbirds are go! F.A.B.

If fifth is geared for a reasonable top speed you may have been a long way below peak engine efficiency in fifth with a boat on the back. Peak efficiency is normally close to peak torque.

I've driven a couple of cars recently with economy hint lights. One of them basically doesn't want you to engage top (6th) unless you are on a motorway.

Andy

That was what I was thinking Andy.

I've not seen one since that Mk3 Escort. ;-)

I can quite understand it.

And seeing the result of that is why I think some people ought to be taught how to use them and how to work the engine around them.

What I mean is they short shift though the gearbox to the highest gear available, keeping the revs really low as they do so (and I'm talking of ordinary / petrol cars here where that would be as you say, well below it's most efficient band) and then take the revs up to whatever is required for 70mph in top?

Why not take it to those revs though the entire gearbox and get out of everyone's way quicker!

Cheers, T i m

p.s. When I had the 1.6 Mk5 Cortina estate I was often going for a higher gear (of the 4) that I didn't have. When I got the 5sp 2L GL Sierra Estate, I often traveled reasonable distances before I remembered I had another gear! eg, even 4th on the Sierra seemed longer than 4th on the Cortina.

On Sunday, 5 January 2020 21:36:51 UTC, Vir Campestris wrote: <>

Whereas my car gets itself to 7 (top) very readily. And drops two cylinders if it doesn't need much power.

Annoyance with mine is that to use 6th I really need to be doing over

1. S***ty gearing ratios :( Only upside is that passing stuff upwards of 90 is a breeze.

On my last car, a BMW, with this Bosch temperature guage, you could make the OBC read true coolant temp. Which had a range of more than 10C with the dash gauge reading exactly mid way.

At one time pretty well every car could be damaged by over-revving the engine. Even the smallest ones.

Bollock:-)

Mind you it only did 79 miles last year.

Best to pass. The closest resemblance of her arse was the rhino at Knowsley Safari Park.

You may misunderstand me. These are little sections of the LCD screen that replaces the instruments that light up (or to be precise, un-darken)

Andy

Possibly.

So, why do they do that and how do they hint at economy?

On the Escort 'Economy' the 3 LEDs were connected to the inlet vacuum somehow so that as that changed (as you increased / decreased engine load) the lights reflected that.

Gentle with the throttle and acceleration or being in the right gear at the right time and you just might keep the green light on.

To drive without causing an obstruction you would generally see the red light on. ;-)

Cheers, T i m

What factors do economy (gear-change) lights on modern cars take into account. Do they just encourage you to keep the engine revs between certain limits, or do they also take into account the load on the engine - ie do they tell you to change down on an uphill gradient where the engine load will be greater than for the car on the level at the same engine speed and gear?

Mine takes into account upcoming road junctions and lower speed limits.

I suspect they have no function whatsoever except to give the car a go greener virtue signalling stripe

Back in the day a vaccuum gauge was a good indicator for normally apsirated petrol.

Or a mirror loking at the exhaust smoke on a diesel.

OK. What factors are used in determining when an automatic gearbox changes gear? I imagine engine load, throttle position, engine speed and road speed. It is likely that a manual car with change-up/down economy indicators will use those same inputs, with a certain amount of latitude (hysteresis) between the values which activate the change up and change down indicators.