1HD-T Chronic Low Oil Pressure at Gauge Fix

Discussion in 'Diesel Tech and 24 volts Systems' started by 83bj60, Aug 20, 2008.

  1. 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.

    Prying off the Can from the Sensor Flange.jpg

    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.

    The Sensor.JPG

    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!

    The Contacts aren't Touching!.JPG

    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 :)
    Prying off the Can from the Sensor Flange.jpg The Contacts aren't Touching!.JPG The Sensor.JPG
  2. sandcruiser


    San Francisco, CA
    good writeup, thanks!
  3. Tapage

    Tapage Club 4X4 Panamá SILVER Star

    Wou .. one day, I will take time to do that .. since I run my ISSPRO setup and have the facotry oil press sender much more accesible in the top of my DS fender ..
  4. OK... after driving the truck this afternoon this is what I noticed: you don't want the contacts to actually touch at rest. That may give you a slightly off-zero reading...

    Secondly, I notice that the oil pressure is slightly above the first mark at idle and slightly below the second mark at 2000 RPM. Although it may be just fine, it would seem to me that the response band is fairly narrow (assuming correct oil pressure), confirming the theory that the main issue with these sensors is not mainly contact wear but loss of bimetal response after so many million bending cycles.

    I will keep looking into it, of course, and I'll test my spare sensor also but it may well be that these sensors just loose sensitivity with time and that it may actually be more cost effective to replace the sensor with a new one.

    Unless the inline resistor was replaced or adjusted to compensate for the lack of bimetal sensitivity, hehe ;) ;) ;)

    On further thought, if the resistance value of that inline resistor was decreased, the bimetal would not heat so much and cycle less often, increasing the time power is applied to the dfash bimetal ;)
  5. They are under $20 now if you know where to look. My $30 sensor has lasted 4 years..
  6. Great! Do you have a part number you could share? My wife is going to the US this weekend and she could pick one up...
  7. amaurer

    amaurer SILVER Star

    Longmont, CO
    Neat thread. I think mine is ready for replacement, I was excited to just open it and adjust it but as you note I'm sure fatigue life is an issue. So where are these cheap ones from?
  8. I've looked it up on ebay, and they are scarce! Saw only one, it it was used... No thanks!!!

    My next test will be to mod the existing resistor (I have some wire wound rheostats that could help determine the required fixed resistor)... When I actually find the time to fix it!!!

    Another trick I might try is one that I've learned from my electronic club days, which is to take a file to the resistor to increase its value, without removing it from the circuit. That would reduce the bimetal cycling (less power to the heating coil = less OFF cycling) which would in turn increase avaliable power to the dash gauge bimetal heating coil, that would in effect amplify the effective response on the gauge.

    In any case all this is pointless if you don't have a way to actually test the sender at known pressure setpoints, for example, with air applied at given pressures...
  9. BlueHZT60


    Bend, OR
    Interesting. When I did the 60-HZ transplant we used an old 60 series sender. It worked for about 6 months - reading in the 1/2to 1/3 zone. It pooped out, I bought a new 80 series sender and now the pressure reads bottom 1/3 all the time.

    I did notice the 60 sensor input hole was about the size of a ball point pen tip, while the 80 series was much closer to 7mm pencil size. FWIW, it made a difference on the dummy gauge. Maybe next oil change I'll futz with putting a modified 60 sensor back in and see what happens.
  10. All over SE Asia. A importer I know said most of them are ok except the Thai sensors which sell for $7
    Ive never been let down by Taiwanese parts.
    IMO they are number 2 at making car parts after Japan
  11. Ron R

    Ron R

    The Netherlands

    Is it an option to remove some of the windings around the bimetal without shortening the heating wire? This way the bi-metal is less heated as well and total current is slightly higher.
    This way the modification is reversable.
    Eventually the heating wire could be unwinded/shortened.

  12. sandcruiser


    San Francisco, CA
    I think I remember hearing once that the Tercel has the same oil pressure sender?
    Maybe it was the Camry. Either way, I'll bet that there is a crashed one near you right now and $5 at the junkyard may do the trick.

    I'm going to stick with adding an aftermarket guage. It may or may not be more accurate, but I like to have 2 so that if 1 is reading extra low, I can at least arrest the panic if the other reads OK.
  13. Brilliant idea, 'why didn't I think about it myself', :doh: ... The heating coil is soldered so I presume it should be easy enough to actuallty unwind without breaking... I'll try on my spare sender tomorrow...
  14. Yes those senders are shared by quite a few engines. But getting a used one, knowing how unreliable they are, gets you a good chance of falling on a dud. I got a used spare from a fellow mudder specifically for that and it was actually worse than my OEM was. In any case it would be great if the parts scavengers would actually charge only 5 bucks, I don't know how it is in your area, but here there is a network of used car dealers, they talk to each other and they all charge about the same, that is, as much as they can possibly get away with.

    I don't like aftermarket, looks too shabby... I'd LOVE to find a 'design yourself' dash of the proper size that had as good integrated lighting as the original dash is (whcih is not easy to accomplish).
  15. John Galt

    John Galt

    Coldest N. America
    How much does it cost for a new one?
    What's the part number?
    Is it the same OP sender as the Cdn BJs?
  16. I haven't asked around here but I will call Prime Toyota in Maine tomorrow and see how much I can get it for. Roodogs in OZ sells them for $69.05 on ebay AU.

    The part number is 83520-60010 and it is widely used on engines of the 6X, 7X and 8X series, and it may fit other Toyota trucks and cars. Has a grounding wire tab. There is a variant 83520-60020 which I believe is for 24V versions, but that's just a hunch, don't quote me on it. The earlier model (pre 1983) is 83520-55011 and it has NO grounding tab but appears otherwise identical, used mostly for 4X, 5X and some early 6X series.
    Last edited: Aug 24, 2008
  17. Dutchie


    Sneek, Holland
    Old topic but I found out my gauge is fine, just the sensor seems not to send anything through to the gauge. Bimetal is working... and with a test lamp as per manual the gauge works too. All connections are OK, capacitor is fine... and yes, there is oil pressure :)

    Could the resistor in the sender be too much Ohm? Measured 200 Ohm and I did find there's old and new type senders.... Will a LOWER resistor send more signal to the sender ??

    Edit : Just took the resistor out and replced by a 10W bulb which has a 3.5 Ohm resistance and the gauge shoots up... so I gues I'm going to get myself a 200 Ohm micro potentiometer, hook ik up instead of the resistor and have play.... untill I get what I want on the gauge.
    Last edited: May 30, 2009
  18. Dutchie


    Sneek, Holland
    Update : The above worked well with the potentiometer ! Had all working and then decided to make a little hole in the sender housing before putting it back to enable me to adjust later when needed....

    Well, when adjustung I short circuitet the loop and now the gauge itself it stuffed :( :(

  19. Great solution! Too bad you shorted it out... At about what position on the potentiometer did you get the best results? in other words, what aproximate resistance value works best? I would think one would neeed a fairly beefy potentiometer (the kind made with resistance wire on a ceramic core), considering the amount of current used drawm by the device... Something able to withstand a few watts, for sure...
  20. Dutchie


    Sneek, Holland
    Well... I was trying for the best result but before I got that I got the worst....

    See pic, original without cap and blue trimpot instead of resistor on left (when it was still working) and VDO sender for the MADMAN gauge on right. Hose came with the gaude, makes it a bit easier to work on :


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