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Talking about a car with a manual gearbox: I find it useful to know how many revolutions I am traveling with the engine as it allows me to know what rpm is more relaxed for the engine.
Exactly how do you determine when an engine is "more relaxed" - (presumably you mean less stressed) - using a tachometer?

Different engines are built to operate under different operating conditions - american manufacturers have traditionally built larger displacement, slower revving motors, the japanese tend towards smaller displacement, higher revving motors - there are numerous forum posts where newcomers to the Suzuki brand have questioned the higher rpms of their vehicles, and pretty much all of them have the same response - don't worry about it, these motors are designed and built to run that way.
 

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My car has a Renault 1.9 euro 5 engine .
Turbo specs says:
129HP @ 4000RPM300NM @ 1750RPM

Between 1750 and 2500 rmp, the engine works relaxed, as you have the maximum torque available against the environment. You can go beyond that, of course, but the temperature will increase, the oil consumption as well. This is a common symptom of diesel engines. They are designed to turn slowly, and people drive them like gasoline engines.

This graph is in German, but everybody understands the numbers, at least, those who are interested in the car data. I couldn´t find the same in english.

Saying that, I can know that if the engine is at 2000 rpm, I should not downshift to overtake.

101339



Also, for fun, you can calculate your speed based on engine revolutions and gearbox ratio, and verify it with the speedometer or GPS ;)

An example from the J24B engine:
101340
 

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Another use for a tach on an older automatic for more technically-astute owners is to ascertain the state of the torque lock-up convertor clutch while towing, or even while driving up long hills at highway speeds. By watching for the sudden approx 200 hundred RPM increase you'll know the moment it's better to drop into 3rd (O/D off) where the lock-up will quickly re-engage and avoid the rapid increase in oil temperature that results.
On my 2000 Nissan Xterra I once measured 1°F increase per second when going up the Tejon Pass in California at around 70 mph when I intentionally allowed this to happen. Within one minute it was in overheating territory. Many drivers of older 4 and 5 speed autos would not be aware of this subtlety because the engine will pull fine in top but the trans suffers silently. Newer designs are a bit more clever and close the TC clutch in nearly all of their many gears.
 

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Discussion Starter · #24 ·
So an alternative to the tacho might be a gearbox oil temperature gauge (measuring in degrees Centigrade naturally) ? As it will tell you the same thing. And since we are in the digital age the temp gauge could allow you to preset temperatures that you are worried about. So if there is a temperature that it is known where the gearbox works the best (fluid mechanics etc) your meter could have a green area and as long as the gauge is within that point you are good and running maximum efficiency and maximum fuel economy. If the designers know where the good spot is an alarm preset could be set to ding when you approach/go over so you know when you are into danger territory. No need to continually watch a tacho. Sounds good to me. Of course just one more thing to go wrong and require an expensive repair but that doesn't stop them from building in all sorts of 'thingys' of dubious use. I would rather have that instead of a tacho.
 

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I've never driven with a precise temperature gauge for water or oil. I imagine there's a time lag and hysteresis in their output compared to an instantaneous change shown on a speed or revs display. Can someone experienced please address that question.
 

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Discussion Starter · #26 ·
It would depend on what you are measuring and why you are measuring it whether hysteresis is important or not. For example if you were towing a caravan with an auto your transmission will heat up. But it won't happen in a second so reporting delay not so important. I won't discuss a speed display since this is probably only used to keep traffic fines low. I can't think of any situation that I have been in (now that is ME) where instantaneous reporting of revs would have helped me. Temperature reporting different matter. Those absolutely crap vehicle temp gauges that only show you something is wrong when it is already too late should be banned. It might be of some concern with the speed of the actual sensor if you were concerned about the effect of loss of water (hose burst for example) but here a water present sensor or water pressure sensor would be more useful. A tacho might be okay but it will only show you when you have reached zero revs when the engine has seized.
But as has been pointed out here earlier whether most people would even understand what the gauges are telling them is of concern.
The one thing that needs to be understood is now it is possible with a little bit of software and some sensors to give you complete control/reporting of your engine. With the cost spread over a couple of million engines it is bugger all. Almost the same system could be used over wide range of engines minimising design costs. Whether anybody will bother who knows.
 

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Another gauge I use will probably be laughed at - the instantaneous fuel use linear slide graph. This and the revs dial tells me whether I'm straining things more than needed. Sometimes I step down a gear and reduce accellerator, see no diffence in road speed, and the thing appears more relaxed using less fuel. That's in my non-professional mechanic perception. Usually with a more sweet sound from the engine.

This thread discussing gauges and indicators - Whatever happened to the lever to adjust spark advance timing on early automobiles that my grandfather & brother's company built in the early 1900s, or the choke that was needed in the morning when I got my licence in 1963.
 

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I've never driven with a precise temperature gauge for water or oil. I imagine there's a time lag and hysteresis in their output compared to an instantaneous change shown on a speed or revs display. Can someone experienced please address that question.
Before we even get to hysteresis and lag in the measurement system, we need to remember that the fluids have "thermal mass" - it takes a tremendous amount of heat energy to instantaneously raise the temperature of a large volume of liquid (the average automatic transmission contains well over a gallon of fluid), alternatively a smaller amount of heat energy will take considerably longer to raise the temperature of the same amount of fluid.

The intensity of debate on transmission temperature gauges, whether or not to fit one, and where to fit the sensor, is akin to politics & religion (and so apparently is the need for a tachometer on todays cars), and I can tell you, having fitted one (reasonably precise, with numbers, sensor in the fluid out line to the cooler, where it will respond quickest to the change in fluid temperatures), that it is by far, the most useless gauge in that vehicle, more useless in fact that the tachometer that was fitted at the factory.

I'll come back to the transmission temperatures in a minute.

From the factory this particular vehicle, a Mitsubishi Pajero iO comes with a tachometer, speedometer, fuel & coolant temp gauges, and the usual array of warning lights, oil, charge, CEL, ABS, SRS, transmission selection & low fuel - because this vehicle has Mitsubishi's "Super Select" 4WD, there's a little graphic showing whether it's in 2H, 4H, 4HLc or 4LLc - and this vehicle will indicate a transmission over temp by flashing the neutral light in the cluster.

Additional gauges fitted after purchase are an oil pressure gauge, a voltmeter, and the transmission temperature gauge described above.

Why did I fit additional gauges, do I use them, do I need them - I fit additional gauges to my vehicles because I like to monitor the "vitals" - do I need/use them - on one trip out of the city in this vehicle, coming down a hill I saw the oil pressure light come on - internet lore says by the time you see that light, it's already too late, engine damage has already occurred - whilst I don't personally believe that to be true, I haven't torn an engine apart to check for damage, so I can't say it isn't - what I can say is that I've seen that light come on because of a loss of oil pressure caused by low oil level (comes on & goes off when you turn a corner and the oil sloshes around in the pan, covering & uncovering the pick up) and that engine survived for many years after - but back to my story - a glance at the oil pressure gauge showed that I had oil pressure and that the oil pressure switch had failed - I went through three or four switches in a six month period - so yes, I use that gauge.

I've also discovered that there is a noticeable correlation between oil pressure at idle and ambient temperature - once the engine is at operating temperature, the hotter the day, the lower the pressure at idle.

You can consider oil pressure in your engine to be akin to blood pressure in your body, early detection of low oil pressure can make a major difference to the size of your repair bill, in the same way that early detection of high blood pressure can make a major difference to your medical bills.

Volt meter - I've had a battery with an intermittent bad cell - my daughter was using the car, I was out of the country - she reported having to randomly jump start it - it would work fine one day and need a jump the next, it would need a jump start now, and start just fine the next three of four tries. She jumped it to drive to the airport to pick me up, it started fine on the trip back home - next morning I switched the ignition on and looked at the gauge, a hair over 10V, a bad cell, time for a replacement.

Back to the transmission temperature gauge, that was the last gauge fitted to this vehicle. This was the first vehicle I owned with an automatic transmission, I had driven many before, but never owned one - I've read all the hype out there, don't flush the transmissions, don't let them overheat, fit a temp gauge it'll save you a ton of grief, don't fit the gauge sensor in the pan that's not the temperature you want to know, fit the sensor in the pan because you want to know the temperature of the fluid going into the transmission not coming out, if you fit the sensor in the line to the cooler you'll never know if the cooler is working, fit the sensor in the line to the cooler, it'll show you how hot the transmission is getting - etc., etc. etc.

My recommendation is if you have a 4WD with an automatic transmission and you plan on towing or expect to be in heavy sand frequently, fit a temperature gauge and fit the sensor in the line out - that way you will know how hot the fluid is getting, you'll be measuring the fluid at it's hottest.

Why am I recommending you fit a gauge after saying that mine was useless? It's the only way you'll know if your transmission temperatures get high enough for you to be concerned - you're running a different vehicle to me, in a different climate to mine, with a different load and in a different off road environment - this particular Mitsubishi uses an AW4 transmission, rated for use with engines twice as large, the chances of me destroying it with the original engine are extremely low.

What to expect from your transmission temperature gauge - a very, very gradual rise in temperature - more gradual than the rise in temperature you'll see on your coolant temperature gauge - the only way I know to be able to actually watch the transmission temperature climb is to force it by doing a prolonged torque converter stall test, which I don't recommend - my "around town" trips are generally too short for my transmission to reach operating temperature and that's with the fluid being warmed by the heat exchanger in the radiator bottom tank - longer trips I'll see the temperatures rise, but, never high enough to cause concern, I'll see it creep up in traffic, and gradually cool down once the traffic eases - and in my case, I know, regardless of what I'm doing with the vehicle, I don't need to concern myself with transmission temperature.

Yes, I admit, had I not fitted the gauge I would not know how close to (or in my case far from) overheating my transmission was under my usage patterns - maybe I should have just done as most Pajero owners do, and trusted Mitsubishi's judgement. Actually I have very good reason not to trust Mitsubishi's judgement, but, that's a story for another forum.

Back to the tachometer - yes - I've used it to determine if/when the torque converter clutch engages - but anyone who thinks that they can detect that 200 (or so) rpm change by watching the tachometer is a danger to both themselves and other road users, because they're going to be paying more attention to the tach than the road ahead - personally I flip the OD Off as soon as the vehicle starts to slow going uphill, forcing a down shift to third rather than allowing it to labor up the hill, and I don't need a tach to tell me when that happens, I can do it by ear.
 

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Those absolutely crap vehicle temp gauges that only show you something is wrong when it is already too late should be banned. It might be of some concern with the speed of the actual sensor if you were concerned about the effect of loss of water (hose burst for example) but here a water present sensor or water pressure sensor would be more useful.
Back when I did GDS support I was on my way to a service call and saw the temperature gauge on my Suzuki Swift start to climb, I was about a block from my destination so I continued, pulled into the parking lot, switched off and opened the hood - top hose was gone - I called my wife and asked here if she could drop a replacement hose and a gallon of coolant to me on her way back from lunch - I had both items on the shelf - I went into the customer, resolved their issue, came out, collected the hose & coolant from my wife, fixed my issues, and continued with my day.

How did I know I had a problem? That same "absolutely crap vehicle temperature gauge" that Suzuki fitted at the factory.
 

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Another gauge I use will probably be laughed at - the instantaneous fuel use linear slide graph.
I actually use this quite a bit - a couple of times a year, we "road trip" using rental vehicles - it doesn't take long to figure out what's the best road speed to achieve a good compromise between fuel used & estimated travel time.

This thread discussing gauges and indicators - Whatever happened to the lever to adjust spark advance timing on early automobiles that my grandfather & brother's company built in the early 1900s, or the choke that was needed in the morning when I got my licence in 1963.
I think those two were among the first to go - along with the hand crank - making cars easier & safer to operate - safely hand cranking a gasoline engined car is something of a black art, not at all like pull starting an outboard, or kick starting a motor cycle.
 

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Discussion Starter · #31 ·
Water and transmission fluid temperatures are somewhat intertwined (on an auto anyway). On both my 300zx and my Surf I had various problems with overheating. If one overheats it will affect the other. Fixed the 300zx by fitting a transmission cooler (cheaper than a new radiator) and the Surf was fixed when my son drove it over a bank. The 300zx had an actual oil pressure gauge fitted and it was very useful (not just a go/nogo). You knew when the engine was at temperature by noting the oil pressure rather than the water temp go/nogo.
On the 300zx I knew I had water temp problems when the steam rose from the engine bay - you saw that before the temp gauge told you anything useful. Once I had to pull into a Toyota dealers carpark to refill the radiator (took a couple of minutes to lose the feeling of embarrasment). Solved when I found a ball of dirt had formed into a pellet and was acting as a one way valve inside the overflow tank.
Even when 'testing' the 300zx I never used the tacho because the auto sorted that.
I used to hand crank a Morris Minor engine sometimes in my early days. Along with using a choke. Didn't seem particularly wrong then but you wouldn't do it now.
 

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Water and transmission fluid temperatures are somewhat intertwined (on an auto anyway)
Most automatics have a transmission "heat exchanger" in the radiator bottom tank, used to warm the transmission on a cold day, and cool it if it runs too hot - the coolant temp gauge on my Pajero will get to "normal" within a few minutes (less than ten) of move off on my morning commute, long before the transmission temp gauge gets "off the peg" (100*F), and I've never seen the transmission temp go higher than 200*F

I used to hand crank a Morris Minor engine sometimes in my early days
Pull up or push down?
 

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Discussion Starter · #33 ·
From memory it was a pull-up although I think it depended on which side you inserted the crank handle. It can best be called a 'bitch' of a job especially as the engine was further modified and I didn't keep up the requirements that needed to be done at the same time.
 

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I never even look at it. If the car let's you go past redline you got other problems. Both manual and automatics have rev limiters and if you hit the rev limiter and hold it there maybe you should have passed on that last drink.
 

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My car has a Renault 1.9 euro 5 engine .
Turbo specs says:
129HP @ 4000RPM300NM @ 1750RPM

Between 1750 and 2500 rmp, the engine works relaxed, as you have the maximum torque available against the environment. You can go beyond that, of course, but the temperature will increase, the oil consumption as well. This is a common symptom of diesel engines. They are designed to turn slowly, and people drive them like gasoline engines.

This graph is in German, but everybody understands the numbers, at least, those who are interested in the car data. I couldn´t find the same in english.

Saying that, I can know that if the engine is at 2000 rpm, I should not downshift to overtake.

View attachment 101339


Also, for fun, you can calculate your speed based on engine revolutions and gearbox ratio, and verify it with the speedometer or GPS ;)

An example from the J24B engine:
View attachment 101340
You've got issues if yours is using oil, I drop my oil every 7500km in my ddis and it's still on the same mark on the dipstick. I drive it hard and it's towing a work trailer daily.
 

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Hand cranking - I remember my father usually setting it to down first on the half rotation from 3 to 9 on the clock for our circa 1950 Vauxhall Velox. I still have his tyre levers, vulcanising clamp with a few unused tube patches, battery acid hygrometer, and lever activated pressure greasing gun. I wonder when OBDII analysers will be considered as quaint antiques.
 

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Hand cranking - I remember my father usually setting it to down first on the half rotation from 3 to 9 on the clock for our circa 1950 Vauxhall Velox.
Are you sure it was down?

There is always a temptation to use your body weight to help turn the engine over, the danger there is if/when the engine fires and kicks the crank handle out, you'll overbalance and fall face down - if you're pulling up, there's a lot less chance of getting hurt in the process - this is how you know who's been doing it before.
 

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Discussion Starter · #39 ·
Cranking is one of those life experiences I prefer not to remember. Didn't have to do it very often and I think it was when any/all of these weren't right and it needed that extra pull - carburettor, distributor, choke not set right, very cold weather, when it was your turn to have a shitty day, and others. A pull was easier to handle than a push when it backfired. Can't remember direction.
 

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Pull up is the method taught so that a kick-back doesn't break your wrist. It's clockwise looking from the front.
Not that I've ever needed to do this but my Austin A40 I owned in the late '70s had a crank handle for backup.
 
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