It seems that every time you read about someone getting one of those great Land Cruisers, invariably the oil pressure gauge turns out reading too low. As you've probably found out reading the forums, it usually is a gauge problem (remember how amazed you were when you first heard that engine purr... 'is that really a diesel?')
Because I always found that installing aftermarket gauges was the wrong approach to fix the problem and because I believe that even without actual figures, well operating gauges can be just as useful as ugly aftermarket gauges with their (not necessarily more accurate) numbers, I decided to look into it a bit closer. In the end, though, this could not have been done without the pioneering work of Towpack who recently posted a picture of a sensor with its cap removed and gave me the impetus to fix mine and write this report.
The bonus is, I found out from doing this fix on sensors coming from two different truck models, and looking it up on the net, that this sensor is generic to many Toyota models so this fix can be used for many other (12V) configurations besides our JDM landcruisers
So for all of you pigheaded folks who hate to unnecessarily fork out money to our dear gouging Canadian Toyota Dealer, with further ado, here is how to fix your chronic low pressure indication
First of all, what's the cause of the problem? The sensor is made of a pressure device which pushes a contact against a bimetallic strip heated by a wire coil. The principle is, the greater the pressure, the longer heat has to be applied to the bimetallic strip to cut the circuit feeding power to the dash gauge. That dash gauge consists of a needle that is moved by another bimetallic strip heated by a wire coil. The design is admittedly not very accurate, but it's very robust when compared to a D'Arsonval meter movement. To sum it up, it works pretty much like the old mechanical regulators, cycling between applying power and cutting power to bend and relax the bimetallic strip maybe a thousand times every hour.
So as the sensor ages, the contacts wear and the bimetallic strip gradually looses it initial elasticity and eventually doesn't bend like it should anymore, eventually causing a situation whereby the contact can't get back closed at rest anymore, causing the sensor to require extra pressure before it will start feeding the dash gauge with current, causing the appearance of low oil pressure when it is not the case. Fortunately, there is a provision to adjust that gap back to normal within the sensor, and this is what we are going to do to fix the problem. You see, Toyota didn't make poor gauges after all. They just didn't make them easy to adjust after 15 years!
So, how is it done? On the 1HD-T, the sensor is to the right of the oil filter. It is not easy to access. Basically, you have to remove the oil filter to be able to get to it, and to remove the starter mud screen from below. So it's a job you'll want to do when the doing an oil change.
As there is no practical access to the sensor tightening nut, I used a pair of adjustable pliers to grip the sensor at the flange (not the end of the cap, which is made of very thin metal) and unscrew it. It was actually quite easy to remove it this way. Of course, you have to remove the connectors first
Once the sensor is out, you will notice the sensor consists of a can with external contact, pressed onto the flange of the body of the sensor, so you will have to gently pry it off to access the insides. To do that, first gently unbend the 4 tabs that lock the can to the sensor flange, then using a pair of pliers, gently pull the lip of the can off the flange until there is enough room for you to insert a flat screwdriver blade to pry it off.
Take your time to do it right, as you are going to reuse the can and need it to be in the best possible shape for reinstallation. It will eventually pop off in a few minutes of gentle prying.
Once inside, you will notice how elegant the design is.
There is a rubber disk seal on the flange and it has probably kept the inside quite clean. Careful, don't lose it, you will need it when putting everything back together. The sensor itself includes a piston pushing a contact against a bimetallic strip around which a white coil of wire is wound, a toothed wedge-shaped wheel for adjustment, a resistor and a flexible contact strip contacting the central pin insulted from the can feeding the dash gauge.
If your sensor was giving abnormally low reading, you will notice, surprise surprise! A substantial gap between the contacts of the bimetallic strip and the pressure actuated bottom contact. No wonder it takes pressure before it will even get off the zero mark, and that high pressure reads so low!
Next to the contact on the other end of the bimetallic strip you will notice a ball pressing against a sloped wheel. You guessed it, that's how the contacts are adjusted. There is even a provision for using a splined adjusting tool, but using a screwdriver blade will do just fine.
Simply use the tip of the screwdriver on the teeth of the wheel to rotate it so that the bimetallic strop lowers down until the contacts touch. It's that easy!!!
But wait, I hear you say - what about the contacts? Shouldn't I do something about them? Well sure! But as they only carry low voltage and no high induction, they are not burnt, just worn a bit. So I simply pass a 400 grit wet and dry sandpaper to clean it a little and voilà...
After the contacts are adjusted back to where they should be (just touching), I bend the top contact tongue a bit to give it more positive contact with the central pin before closing the can onto the flange of the sensor.
I put the can back not forgetting the rubber ring and bend the 4 locking tabs gently but very firmly with a pair of narrow pliers (I don't think this job can be done more than once before the metal tabs break, so it may well be a single repair, unless a better way is devised to better fasten the can to the sensor flange) then I tap and shape the can lip back onto the flange.
Be aware that if you do not do a very sturdy job there, it is possible that the sensor may come loose when you tighten it back wit the pliers when reinstalling, which could cause it to leak and the contact to be poor. Ask me how I know this
In any case once reinstalled and reconnected you will notice that the gauge will now read the way it should: second mark when driving, and first mark when idling. Well, not exactly: your oil being fresh and cool may read up to half at idle until the engine warms up, but you knew that
I'll let you know how it behaves in different conditions over the next few days.
Hope you enjoyed this report
Because I always found that installing aftermarket gauges was the wrong approach to fix the problem and because I believe that even without actual figures, well operating gauges can be just as useful as ugly aftermarket gauges with their (not necessarily more accurate) numbers, I decided to look into it a bit closer. In the end, though, this could not have been done without the pioneering work of Towpack who recently posted a picture of a sensor with its cap removed and gave me the impetus to fix mine and write this report.
The bonus is, I found out from doing this fix on sensors coming from two different truck models, and looking it up on the net, that this sensor is generic to many Toyota models so this fix can be used for many other (12V) configurations besides our JDM landcruisers
So for all of you pigheaded folks who hate to unnecessarily fork out money to our dear gouging Canadian Toyota Dealer, with further ado, here is how to fix your chronic low pressure indication
First of all, what's the cause of the problem? The sensor is made of a pressure device which pushes a contact against a bimetallic strip heated by a wire coil. The principle is, the greater the pressure, the longer heat has to be applied to the bimetallic strip to cut the circuit feeding power to the dash gauge. That dash gauge consists of a needle that is moved by another bimetallic strip heated by a wire coil. The design is admittedly not very accurate, but it's very robust when compared to a D'Arsonval meter movement. To sum it up, it works pretty much like the old mechanical regulators, cycling between applying power and cutting power to bend and relax the bimetallic strip maybe a thousand times every hour.
So as the sensor ages, the contacts wear and the bimetallic strip gradually looses it initial elasticity and eventually doesn't bend like it should anymore, eventually causing a situation whereby the contact can't get back closed at rest anymore, causing the sensor to require extra pressure before it will start feeding the dash gauge with current, causing the appearance of low oil pressure when it is not the case. Fortunately, there is a provision to adjust that gap back to normal within the sensor, and this is what we are going to do to fix the problem. You see, Toyota didn't make poor gauges after all. They just didn't make them easy to adjust after 15 years!
So, how is it done? On the 1HD-T, the sensor is to the right of the oil filter. It is not easy to access. Basically, you have to remove the oil filter to be able to get to it, and to remove the starter mud screen from below. So it's a job you'll want to do when the doing an oil change.
As there is no practical access to the sensor tightening nut, I used a pair of adjustable pliers to grip the sensor at the flange (not the end of the cap, which is made of very thin metal) and unscrew it. It was actually quite easy to remove it this way. Of course, you have to remove the connectors first
Once the sensor is out, you will notice the sensor consists of a can with external contact, pressed onto the flange of the body of the sensor, so you will have to gently pry it off to access the insides. To do that, first gently unbend the 4 tabs that lock the can to the sensor flange, then using a pair of pliers, gently pull the lip of the can off the flange until there is enough room for you to insert a flat screwdriver blade to pry it off.
Take your time to do it right, as you are going to reuse the can and need it to be in the best possible shape for reinstallation. It will eventually pop off in a few minutes of gentle prying.
Once inside, you will notice how elegant the design is.
There is a rubber disk seal on the flange and it has probably kept the inside quite clean. Careful, don't lose it, you will need it when putting everything back together. The sensor itself includes a piston pushing a contact against a bimetallic strip around which a white coil of wire is wound, a toothed wedge-shaped wheel for adjustment, a resistor and a flexible contact strip contacting the central pin insulted from the can feeding the dash gauge.
If your sensor was giving abnormally low reading, you will notice, surprise surprise! A substantial gap between the contacts of the bimetallic strip and the pressure actuated bottom contact. No wonder it takes pressure before it will even get off the zero mark, and that high pressure reads so low!
Next to the contact on the other end of the bimetallic strip you will notice a ball pressing against a sloped wheel. You guessed it, that's how the contacts are adjusted. There is even a provision for using a splined adjusting tool, but using a screwdriver blade will do just fine.
Simply use the tip of the screwdriver on the teeth of the wheel to rotate it so that the bimetallic strop lowers down until the contacts touch. It's that easy!!!
But wait, I hear you say - what about the contacts? Shouldn't I do something about them? Well sure! But as they only carry low voltage and no high induction, they are not burnt, just worn a bit. So I simply pass a 400 grit wet and dry sandpaper to clean it a little and voilà...
After the contacts are adjusted back to where they should be (just touching), I bend the top contact tongue a bit to give it more positive contact with the central pin before closing the can onto the flange of the sensor.
I put the can back not forgetting the rubber ring and bend the 4 locking tabs gently but very firmly with a pair of narrow pliers (I don't think this job can be done more than once before the metal tabs break, so it may well be a single repair, unless a better way is devised to better fasten the can to the sensor flange) then I tap and shape the can lip back onto the flange.
Be aware that if you do not do a very sturdy job there, it is possible that the sensor may come loose when you tighten it back wit the pliers when reinstalling, which could cause it to leak and the contact to be poor. Ask me how I know this
In any case once reinstalled and reconnected you will notice that the gauge will now read the way it should: second mark when driving, and first mark when idling. Well, not exactly: your oil being fresh and cool may read up to half at idle until the engine warms up, but you knew that
I'll let you know how it behaves in different conditions over the next few days.
Hope you enjoyed this report