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Faced with a standard car with only a warning light or two you would be best to fit a water temperature gauge and a HIGHER PRESSURE oil waming light sender
Higher Pressure Oil Warning Lights
...... like those made by MOCAL/Autolec start to come on at 15-20 psi instead of 5-7 psi as standard
If you are losing oil progressively through a leak the light coming on will tell you the impending death of your engine as you may have driven MANY miles at 7-5 psi, acceptable for idling but not cruising!!!!!
Depending on your driving style a warning at 20psi and half a sump full of oil might just save your engine.. THE DOWNSIDE is the light will likely come on when the engine is hot and idling but this doesn't matter... back it up with a pressure gauge and you know you still have 15psi at idle or whatever ;)
Oil Pressure Gauges
Are either mechanical or electrical, both need an earth wire and a 1/2 amp fused feed that is on when you lights are on ( if you are going to have the gauge lit up)
If you are retaining the oil pressure sensor switch (above) or already have some sort of o/p gauge fitted and want to keep it you will need a "T" or "Y" piece to add the new gauge, test "by eye" the likely best adaptor you need NOTE electrical oil pressure gauges use quite bulky sensors at the engine end.
Mechanical Gauges use a capillary tube to send a column of pressurised oil to the gauge, so long as you route the capillary away from heat and sharp objects and fasten it down it will be the easiest to fit
Electrical Gauges use sensors at the engine end and need a wire to be run to the gauge AND a 12v live feed to power the gauge, ie. only one extra wire 1/2 amp fused from an ignition switched source. These gauges may respond quicker to the rising oil pressure on starting your engine and to fluctuations.
If an electrical gauge fails you will probably have a loose wire floating around under the bonnet .....if it earths out nothing much will happen other than your gauge will flicker
HOWEVER If a mechanical o/p gauge fails you are probably decorating your bonnet with oil!!!!!
ON BALANCE if you are handy with cable ties fit a mechanical gauge, it will be easier to fit at the engine end
Water Temperature Gauges
Mechanical gauges using tubes filled with ether are rare and economically unrepairable once perforated
Replace with a matched electrical gauge and sender
Fitting may need the use of an adapter collar in the head to reduce the thread size
Check the seal on the thread and use PTFE tape to seal as required
Water Pressure Gauges
I once fitted a central heating water pressure gauge to my car to check if the pressure cap was holding 12psi!!!!!
Messy and you have 12psi boiling water in the dashboard if anything goes wrong... not recommended but possible ;)
Oil Temperature Gauges
Only fit if you are using an oil cooler or suspect over/under heated oil
Mechanical (rare) or electrical easiest fitted in line in the oil cooler hose or in a filter head adapter plate, fitting in the sump may give a better "value" of reading, sump fitting ideally as a drilling and adapter collar as using the sump plug to mount it removes the magnetic swarf pick up
Called "Econometers" by some, these can be useful to detect leaks in manifolds state of tune etc. etc., almost always these work with a non collapsible tube leading to gauge in dash from either a 2 piece in the vacuum hose from the dizzy or from a inlet manifold take off, remember if this is taken off the carburettor ensure it is between carburettor butterfly and carburettor, vacuum gauge hoses naturally smell of petrol inside! DO NOT REMOVE any other hoses to fit a vacuum gauge the car my use these other pipes for another function
These are matched to the wheel size and final drive ratio of the gearbox, change these and the speedo will read wrong
They can be recallibrated by noting the number of turns of the speedo cable per 20ft ( maybe) and having the speedo reset
OR go hunting for one from a car with the right calibration ( marked on the speedo face as turns of the speedo cable per xxxx)
Loss of lubrication on the cable or a snapped inner wire can lead to failure, cheap but messy to replace
Tachometers, tachos for V8s or V6s don't work on 4 cylinder minis ( they underread unless switchable) they do not like short circuits, being wrongly wired or some electronic ignitions
They might blow up... take care and NEVER "try to see if this will work" they are not cheap devices to replace
MECHANICAL tachos exist that measure RPM off the cam end... fun to fix need adaptation to the timing cover
Ammeters see here for fitting
USEFUL BUT: Great thick cables passing 40 AMP+ going through your dashboard, fasten them down well!!!
Far more Easy to fit, needs only a live feed useful, compare this with fitting an ammeter
ANY GAUGE WE MISSED: use the feedback below
If you are fitting T to Y pieces or other adapter bushes take the existing sensor to the spares dealer or get it measured as there are lots of threads that look very similar and if wrongly fitted could damage a fixed thread in the block or cylinder head. I have wrapped PTFE tape around adapters to improve the seal on old threads in the past.
Electrical gauges use senders/sensors to vary the degree of "earthing out/resistance" of the wire from the gauge to read the "condition".. these are MATCHED tothe gauges so unless you are an electronics guru make sure you use a gauge with the sender it was designed for.. Otherwise it WILL work but will read WRONG
two gauges on one sender?
NO!! unless a sender is designed for use with 2 identical gauges it will not work right
Checking senders (simple single wire ones on gauges on most minis)
If the wire to an electrical sender unit is removed and earthed out it should result in a full range deflection of the gauge needle (useful to check both gauge operation and integrity of the wiring) IF IN DOUBT don't short it out, ask a knowledgeable friend.
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