Mechanical vs electronic (Smiths) gauges ?

[KevinW]

The original cars had mechanical everything and no fuel level meter.
The mechanical minor gauges usually have a 270 degree swing, whereas electronic gauges have 110? degree swing and different appearance altogether.

Mechanical is considered more accurate than electronic - why is that - just badly matched senders?

Why cant electronic sensors have the full range of swing - works on a tacho?

Your thoughts please.
thanks.
Kevin

[craggle]

Does make you wonder dosen't it?

I went for the mechanical gauges as I liked the full sweep appearance but they are a pain as I now can't remove the dash board without draining the water from the engine and feeding the capillary tube through the bulkhead.

I also wanted an electronic speedo for the accuracy and ease of setting up but I really like the rolling type mileometer.

Whichever way you go is a compromise.

Craig.

[KevinW]

who do you have to drain water from the engine - cant you pull out the capillary end and refit a blank? cant it be fitted at a high point in the cooling system?

any other pitfalls?

[craggle]

The capillary is fixed on the back of the gauge and is a one piece tube until the end which screws into the side of the cylinder head.

I couldn't fit it in the inlet manifold as there was no holes big enough to get the capillary bulb in.

Small price to pay though as I do like the look of the gauges and loads of people wonder why they still register after turning the ignition off and removing the battery cutoff key.

I used the Smiths Cobra range by the way.Original Smiths Cobra Gauges and New Electrical Instruments

Craig.

[KevinW]

thanks for that . What about the other gauges - are there any 'fluid draining' issues there?
what was the problem with just sticking a bung in the hole when removing the bulb?

[craggle]

You could just stick a bung in the hole quickly but you would loose some coolant down the side of the engine block.

The oil temperature bulb also needs disconnecting from the line that runs between my sandwich plate and the oil cooler thermostat. This would loose some oil but nowhere near as much as the coolant system would.

The oil pressure gauge tube can be disconnected from the engine or the back of the gauge so that ones not an issue.

The fuel gauge is electrical so can be simply disconnected.

The capillary tubes on the two temperature gauges are very long though so unless you want to remove the dash panel completely it is easier just to leave them connected and place the dash panel in the footwell or on the floor outside the car. They are long enough to allow this.

Craig.

[Purple AK]

Originally Posted by KevinW

The original cars had mechanical everything and no fuel level meter.
The mechanical minor gauges usually have a 270 degree swing, whereas electronic gauges have 110? degree swing and different appearance altogether.

Mechanical is considered more accurate than electronic - why is that - just badly matched senders?

Why cant electronic sensors have the full range of swing - works on a tacho?

Your thoughts please.
thanks.
Kevin

Electronic Tacho's and Speedo's measure pulses (Frequency/Volts) whereas other minor gauges measure Resistance/Amps. (Someone who has remembered more than I have forgotten over the years will no doubt be along to explain the difference)
Smiths senders don't seem that accurate! I have just replaced my electric oil pressure gauge because if start fuffing around! And the mechanical gauge (verified with another) gives me 80psi whereas the electric one never ever made it passed 50psi!!

[KevinW]

So it sounds like noone knows why Smiths electrical gauges are a bit shite, but empirical observation suggests thats the truth. I cant understand this (unless its simple profit and laziness) - there are plenty of thermocouples and electrical pressure sensors used in industry and critical scientific applications with 1% accuracy or better. Anyone remember the Wheatsone bridge with a thermocouple from school? Not exactly rocket science, or expensive.

[Neil O]

Kevin, I have all mechanical gauges and look and work fine.
I felt that the speedo just had to be mec, because I didn't like the lcd readout at the bottom of the elec one.

It's worth noting that the Crendon dash comes off (enough to work behind it) without disconnecting any capilaries or cables.
If you have leccy gauges, you can unplug everything and remove the dash completely.

[wilf]

Elec guages are shite because for the vast majority of cases, all that is needed is a rough indication, and a good swing from that if temps etc. go haywire. So the manufacturers just don't care. Another instance of quality assurance - you are assured of crap quailty.

There was a good story about some American cars in the 80s - they eliminated any real readings from the dash instruments (they just went to "normal" and stayed there all the time) because when they had accurate (ish) gauges, the slightest deviation from "normal" was triggering a rash of warranty claims.

I found my mech gauges for oil and water temps over read by about 10 degrees, but this is a consistent offset. Oil pressure is spot on.

The reality is that we all tend to become accustomed to the "normal" readings for our cars, and then just keep an eye out for any gauges that deviate from that. Of course Oakers' car will be totally deviant in any case.

Unltimately I chose the mechanical gauges for the 270 degree sweep. (and because that fits better with a Crendon, anyway).

I also can move the dash forward enough to work on things behind it without disconnecting any capillaries - there is enough "spare" length in them to do that, so long as you gather it at the correct place.