Adding coolant temp gauge? (1 Viewer)

[RavenTai]

Ok figured out Thevenin Equivalents as it applies to this circuit (I think) and did one calculation (takes a wile) on paper replacing the 75Ω resistor with a 110Ω resistor gets a 198°F "center" as above and at 226°F gets .3678 volt drop across L1, That is equivalent to the current 235°F position, or about the 3/4 mark.

Hmmm not the bottom of the red where I want it to be……..Lots more math to do. Bed time.

 

[CreeperSleeper]

You guys are awesome. Every time I try to read this thread my head starts to hurt!

 

[landtank]

Ok, I'm heading threw Boston tomorrow and will be stopping by a very good electronics store to pick up a cable to hack into a CVS record once video recorder. So what do I need to get my temp guage modded?

Looks like a 110 ohm wire wrapped resistor, but what wattage. And replace the ZDiode with a hunk of wire. I think it's time for a live testing before you pencil runs out of lead.

 

[semlin]

patience grasshopper, or. he doesn't even have the 93-94 gauge to test bed yet

just bypassing the diode would work for now. If I read it right you won't hit centre until 221 which is almost exactly when the gauge moves above centre now so I think that means you will get a new range of responsiveness below centre but have the virtually same temp response over the centre line as the current guage which is calibrated on the previous page. If ravent'ai has not finished his math by the time you get to boston, I would get an assortment of resisters from 90 to 110 ohms all over 2 amps.

 

[RavenTai]

Ok, I'm heading threw Boston tomorrow and will be stopping by a very good electronics store to pick up a cable to hack into a CVS record once video recorder. So what do I need to get my temp guage modded?

Looks like a 110 ohm wire wrapped resistor, but what wattage. And replace the ZDiode with a hunk of wire. I think it's time for a live testing before you pencil runs out of lead.

The lead on my pencil is doing OK but the eraser has defiantly seen better days.

If you are adventurous enough might be good to get an early test result, just be prepared to redo it later if you are unhappy with the results. Getting ion there is not too bad especially the 2nd and subsequent times.

If you are going to be there I would pick up an array of resistors, all they have between 75 and 120 ohms, wire wound would be best, minimum 2 watt, I would feel better with 3 watt, higher that 3 watts is also OK also but room becomes a problem at some point as they get physically larger with wattage rating.

I ordered my resistors from mouser for less than a dollar each so if you want to wait good quality resistors can easily be had later after your trip to Boston.

If you want I can give you the quick and dirty directions to mod your gauge.

I have a self imposed deadline of getting my truck modified by the 27th of this month, I am hoping to drive on it a bit (10 day driving trip home to FL) before releasing it as a beta to be tried by advanced owners that will hopefully help tweak the directions and trouble shoot any problems before calling it the official 80 series temp gauge mod.

I said earlier I would be done by now but well, it has not happened,

Have a little bit of free time coming both mornings of this weekend; I may have the resistors by then.

 

[landtank]

Give me the down and dirty on the mod and your best guess on which resistor will center the guage and I'll toss it in. I expect to be driving again next week and could easilly monitor your selection for over 500 or so miles next week.

I have another reason to to go into Boston so it's not a waisted trip. Google on CVS Camcorder if interested. Found a v3.4 today

 

[RavenTai]

Sweet, I like it

http://www.makezine.com/blog/archive/2005/08/cvs_camcorder_u.html

Your package is in the UPS system and is on time with a scheduled delivery date of Sep 26, 2005.

bummer, they say no resistors until Monday : ( , biggest question mark I have right now is will the new thermistor match the used one, if two match than we have a better chance of them all being close, I'll try get that done this weekend.

Best guess is 110 Ω , of the two nearby resistors to the current “ideal” 200°F it is the closest at 198°F also it will reduce the current more than a 100 Ω resistor (center 204°F), 110 Ω is not that common, if you only find 100’s then you can try that one or put a 100 Ω resistor and a 10 Ω resistor in series, this is not ideal as you will have a unsupported mid air solder joint witch is potentially less reliable but I will let you make that call.



Rick here are the early directions, they may require interpretation on your end, if something does not make sense let me know.


1 Removing the gauge

Removal is not too bad, the FSM did a pretty good job of getting me through the cluster removal so I will start with the cluster removed, if you need info on removing the cluster shoot me a message.

First the cluster splits in two, the gauges and a white backing are one half, the "glass" and black mask in the other. There are clips around the perimeter lift each one in turn by hand and the two halves will split, after the glass is off be careful not to set it on its face, the cards and needles are kind of fragile. Try not to not touch the face cards of the gauges, fingerprints leave permanent marks.

There are 4 screws (see pic above in the thread) back these screws out partially and then press them with moderate finger pressure. the gauge will seam stuck at first but then will pop up a little bit, if is feels wrong or partially attached stop and give it a good looking over, completely remove the screws and then carefully work the gauge out, it had some slight interference with the tack card but it can be worked out of there. The tach card is semi flexible but do not force it, it might crease.

2 bypassing the Zener Diode

You could completely de-solder the diode, remove it and replace it with a wire, working on the top side of the PCB in that area will be more difficult. An easier and completely acceptable solution is to just bypass it on from the bottom of the PCB find the two solder points of the diode and solder a suitable jumper wire from one point to the other, there is clearance for a small wire on the bottom so no problem there.

The currents this jumper will carry are quite small, a 22 gauge solid or multi-stranded wire would be fine, tined copper would be easier to work with.

3. Replace the resistor

De-solder the resistor and solder in the new one, no polarity to observe so it goes in either way, I would install this one on the top side as the original as it has the potential to get hot, I would also ensure that it has plenty of clearance to other objects for cooling.

4. Check connections (optional)
Measure the resistance from the “U” nut on the back of the PCB to the mount post near the resistor, it should have almost none or about the same as touching you meters leads together

Remove the small brass nut near the “IGN” marking, measure the resistance from the IGN mount post to the mount post near the resistor, it should read near 110 ohms.

Torque for the little brass nuts is medium finger tight with a bare socket (no ratchet)


5 measure and report back resistance of air core motor (optional)

Remove 2 small brass nuts, one at IGN and the other near “U” marking

Measure the resistance from “Temp” to “U” (inductor L1)
Measure resistance from “Temp” to “--“ (inductor L3)
Measure resistance from “Temp” to “IGN” (inductor L2)


6 Reassemble

P.S. wile you are in there check the PCB for charring/darkening around the resistor leads as they pass through the PCB, I have a suspicion that this can be a tell tale sign of an overheated 80 at least on the 96/97.

 

[RavenTai]

Semlin did the removal portion work out OK? do I need to add anything?


Low res, don't worry the final mod will be user friendly only the development is geeky.

 

[Riley]

Given the tolerance of the resistors you might be using, I suggest that guys measure the resistance first with an ohm meter before installing. +-5% of a 100ohm resistor is 95 to 105 ohms and if we know exactly what went in, it should make it easier for others to select a more "refined" value and thus create the ultimate temp gauge mod.

I also wanted to say thanks guys, I've been following this from a far and do apprieciate the effort you all have put into this. I feel like I should have helped.

 

[RavenTai]

I feel like I should have helped.

you just did, yout point is quite valid, Rick may not find 1% resistors, so knowing the actual resistance woudl be a good thing to know

 

[semlin]

Semlin did the removal portion work out OK? do I need to add anything?


Low res, don't worry the final mod will be user friendly only the development is geeky.

the directions were fine and it is very simple. i found it easier to pull the tach/speedo out, but I would have hesitated to do that on my own cluster.

reading your post from last night again i don't think i understand why the 110 ohm resister will not yield the same 26 (or 22?) degree sweep to the red line as the 75 ohm. I thought you had said the sweep will be the same with a different resister just with a different centre point unless you install a small resister in place of the diode? anyway as long as you are sure. it sounds like we would need to play with a small resister or have a higher centre point (higher ohmage big resistor) to get a 226 red line.

 

[landtank]

Ok, I'm on it. I've had the cluster out before for my trip meter problem so I know my way around in there.

I'll try and take all the measurement for you and post back.

 

[RavenTai]

the directions were fine and it is very simple. i found it easier to pull the tach/speedo out, but I would have hesitated to do that on my own cluster.

Since you have now had experience pulling the tach/speedo do you think that is the better way to go? Does the 93/94 have a speedo cable or was that the FJ-80s? When I pulled my gauge I considered but then hesitated on pulling the tach as it looked to have a lot more connections than the gauge and just worked the gauge out.

reading your post from last night again i don't think i understand why the 110 ohm resister will not yield the same 26 (or 22?) degree sweep to the red line as the 75 ohm. I thought you had said the sweep will be the same with a different resister just with a different centre point unless you install a small resister in place of the diode? anyway as long as you are sure. it sounds like we would need to play with a small resister or have a higher centre point (higher ohmage big resistor) to get a 226 red line.

I don’t understand that one either. If I am doing everything right what is on paper should match what the response of the gauge is, right now they don’t match as far as off center readings. maybe I messed up somewhere in that math, it is new to me and I have only done it once, and actually I hope I was wrong as I was thinking the other night "no biggie I will fix it with resistors" but now I remember I can move the red line up by temperature, for instance if it were to redline at 215 I could move it to 226 by using diode replacement resistors but not down further than what is gotten with a jumper (there is no less resistance than 0 ohms) , If 226 does turn up at the 3/4 mark like the Thevenin Equivalents result then I can not move 226 up to the red line. But then again maybe I am getting turned around again, that’s what the test bed if for.

I am not sure of much right now as most of this stuff is awaiting testing. Rick is jumping the gun a bit but that is OK. his gauge will be responsive to all temperature change within the upper and lower limits of the gauge, bypassing the Zener diode assures this, even though I cannot tell him for sure where the red line is temperature wise he can watch the new gauge for a wile and spot anything above normal witch is better than any 80 has had for the past 10-15 years, I am almost certain that his gauge will not be damaged because currents will be less than stock. (at least not damaged electrically, installer inflicted damage is the risk we all will take and is avoidable if you are careful). If this turns out unsatisfactory it can be rearranged later so all he is loosing is his time. But even then we are gaining some early real world results. If all the parts of the gauge are fairly accurate (good manufacturing tolerances) then the 198 degree/110 Ohm center should be correct.

 

[semlin]

the cluster I was working on was completely out of the truck at the wrecker so I can't speak to cable connections etc..

i can't recall if Rick also has an aftermarket gauge but if he does his experiment will yield data. even if he doesn't the main point will be that he has full temp response which will be useful on a "relative" basis.

 

[landtank]

I could only get a 100 ohm resistor and it's going in anyway. I figure you can at least get an idea from where my needle sits when warmed as to how good an understanding you have of what has been done so far.

And I don't have a seperate guage so maybe you won't be able to verify the accuracy to an actual temperature but at least you'll get an idea of it's reponse in the vehicle under normal conditions.

 

[landtank]

well it's installed and tested.

first:

resistor measured 99.7
T - U measured 64.1
T - - measured 45.6
T - IGN measured 59.7


During normal driving the needle was about a needle width below what it used to be. And from what it looks like it did move around a little between idling stopped and driving around.

 

[RavenTai]

figure you can at least get an idea from where my needle sits when warmed as to how good an understanding you have of what has been done so far.


…….you'll get an idea of it's reponse in the vehicle under normal conditions.

Defiantly

well it's installed and tested.

That was quick, nice work.

first:

resistor measured 99.7
T - U measured 64.1
T - - measured 45.6
T - IGN measured 59.7

Ok resistor is within 1%, that is great, but the inductors are quite a bit off from the test 97 gauge, that is not good at all.

64.1 vs 95.3 for L1 way off.
59.7 vs 81.5 for L2 also quite a bit off
45.6 vs 46.0 for L3 dead on

The most disturbing thing there is the ratio of L2 vs L3, the test 97 LX gauge forms a reference voltage of 5.230 volts at the Temp terminal when the gauge is centered. from the above resistances Your gauge forms a 6.279 volt reference at center, which is quite a bit off. With that your gauge would center at about 186F, but you get just below center witch should be right if the gauge centered at 204F.

You did remove the nuts before measurement correct? The inductors need to be isolated from the rest of the circuit or you get reduced readings due to parallel paths.

During normal driving the needle was about a needle width below what it used to be. And from what it looks like it did move around a little between idling stopped and driving around.

Well the gauge still works as expected, that part is very good news and I am glad to hear it, thanks for the info and keep us up to date

 

[landtank]

when you say nuts, do you mean standoffs? Because I left the standoffs in place when I took the measurements.

Anyway would you expect a 110 ohm resistor to center my guage.

 

[RavenTai]

when you say nuts, do you mean standoffs? Because I left the standoffs in place when I took the measurements.

Anyway would you expect a 110 ohm resistor to center my guage.

not the stand offs, but 2 of the 3 small nuts on the back of the air core motor, one or the other would actually do it but both for good measure, also I forgot to say need the washers off also as they would be a conductive path

Reason for this is L3 reads great, L3 is already isolated when you remove the gauge. The other two read about what they would if they were in parallel with the rest of the circuit.

Assuming you took the measurements after jumping the diode and replacing the R1 resistor:

If your 96’s L1 was actually 95.3 but measured in parallel with L2 + R1 in series it would read 62.4 witch is close to the 64.1 you read.

If your 96's L2 was actually 81.5 but measured in parallel with L1 + R1 in series it would read 57.4 witch is close to the 59.7 you read.

Also if your gauge did have those low values for L1 & L2 it would center at 186, (assuming your thermistor is the same) the needle should then read somewhat above middle not just below it at normal operating temperature.


I do think the 110 resistor would move you up that needle width and be closer to the middle. You could order a 110 ohm RS02B110R0FB12 from mouser But if I were you I would go with what you got for now and then readjust it when the mod is complete. As we will then have calibration resistors for you at that point to order. Also possibly D1 replacement resistor And you can check the range.

 

[e9999]

200 posts?

are you guys just having fun and trying to have fun forever or are you actually trying to get this job done?

I hate this gauge as much as the other guy, so tell us what to do already!

I put in a digital display of temp in 5 mins! (so OK, it's flopping around the cabin but it adds a masculine touch to things... )