77RogueRunner

This is kinda a follow up to a previous thread that 84Prerunner started regarding some cooling issues with his swap. It got me thinking about a coolant sender mod, but I need more feedback before I proceed. Right now I have the 88 SR5 cluster and I believe the same resistance values were shared to 8/92 based on the fact that the coolant sender changes to a different part # at that time. That being said, this mod may only work for 88 to late 92 gauges as the 9/92 on should be more accurate as they share the same p/n to the end of production for this engine (88-8/92 is m16x1.5....9/92 on is 1/8 GAS). Here's what I have discovered with my scan tool. The gauge doens't move til approx 130. The needle reaches it's final destination at 164 which on my cluster is pointing right at the 0 tach mark. Although the needle has stopped the temp climbs to 198 which is basically where it stays. If the needle showed this temp on the gauge it would look like I was overheating. I can't use the 88 sender because of the size differences I listed above. I'd like to know if anybody else with an 8/92 or earlier v6 cluster with a scan tool can replicate these results. If these findings are accurate and my cluster is not funky I'm going to look to do a mod that reads the temp accurately. I'm thinking if it starts at 130, stops at 164, but climbs to 198 that's a difference of 34 and 34 to the respective temps so if I half the resistance (or alternately double it...this is what I need to research) I think the gauge will move more slowly to the middle (and maybe past to show the higher temps), but be more accurate through the course. I need some people to run some live data tests on their combo. If you don't have a scan tool but want to check out your combo, Autozone rents them for free (with deposit) and I'm sure other places do too. Once I get some feedback I'll do some tests with a spare cluster and sender and see what can be done. Oil pressure mod to come next....!

hamish_18

I see the same thing on my 90. If you are only wanting the older cluster, sorry about that. But Mine gets up to the normal spot around 165 and stays there until I saw 215 then it started to climb. The vehicle was turned off at 210, but heat soak got it to the 215.

77RogueRunner

Okay that's good info hamish_18, what I'm looking for. I'm not referring to the older cluster in the 1st gen Runners in particular, I'm referring to any cluster from that year with the v6 to 8/92 with the V6. That means your 90 would fall in that category. Anyone else with similar results for these year's clusters?

theMonch

I also am seeing similar results. I just finished my '88 SR5 4Runner swap and the temp gauge jumps up to the normal operating reading for the 3.0 position at about 100 deg and then never goes any higher. I was able to run the truck to about 230 with it never going any higher on the gauge.

Do you know what the voltage range differences are between the earlier 3.0 sender and the 3.4 sender? I am wondering if another resistor mod will cure this like the 10k ohm tach mod. (which worked perfectly on mine by the way)

I am going to go looking on the block/heads for a position to mount the original sender from the 3.0 since it was a seperate sender for the gauge and the ECM on my 3.0. I figure this will be the easiest solution. Then I could just run a wire to the combo gauge and voila!

theMonch

Some interesting reading here.

http://www.toyotasurf.asn.au/techsite/tempgauge.htm

http://forum.ih8mud.com/80-series-te...ification.html

77RogueRunner

Those are some interesting links. I guess that's kinda what I'm going for. I noticed that the second link refers to this working for 93-97 gauges, so that late 92 change-over might inhibit us earlier guys doing that same thing step by step. One thing that I did check out was that at room temp the resistance of the later gauge was twice as much as the earlier gauge. I harvested the temp gauge off my old 4cyl cluster. The wire was like a filiment in a light wrapped around a piece of metal that expanded as it heated up based on the resistance of the sender. As it heated it moved the needle. It looks pureley analog. I attached the new style sender to it and it moved just like the sender mod, but without the mod. Our older SR5 gauges have the 3 screws also in back, the 4cyl has 2 @ 25 ohms across. I'm assuming the guts are basically the same, the resistors just need to be changed out for ones that will work for the ohms the sender is throwing. Here are some pics of my experiment......

77RogueRunner

Here are some snips of the values for the back of the old sender cluster and new sender cluster. Interesting to note in both clusters two resistance values listed for each add up to the other listed. First snip is new sender

77RogueRunner

I couldn't help it so I took apart my cluster to get to the gauge so I could see what I was dealing with. It was pretty simple yet nerve-racking. There is an additional resistor spot not used across the circuit, and there is the Zener diode which after doing some reading, is the cause of the dead-zone in the gauge, then the "avalanche" to the red. To the best of my knowlege the resistor is 75 ohm with 10% tolerance (violet-7, green-5, black x1, silver 10%), maybe 1 or 3 watts. I cannot tell what the Zener diode is as it is so tiny. From my research the zener diodes act in a certain area of voltage depending on the type which is shunting the signal hence the dead zone. The thing I didn't like about the 93 + gauge mod is that 198 (about where I'm running) is gonna be about 3/4 to the red, 212 is at the red when in reality I think that would be an acceptable temp to run. I think this can be cured by using different resistors and possibly a Zener diode in a lower voltage rating making the dead-zone before the gauge even registers for the temp (I have no idea, I pour concrete for a living). In all honesty the M16x1.5 tap in the manifold is sounding good and a lot less electrical, and mybe a bit more reliable if there is room to tap. Despite that, I worked with a guy last year who's wife engineered circuit boards for company's on the west coast. I'm gonna see about getting a-hold of her and maybe picking her brain a bit. That's where I'm at. If there is anybody reading this who has access to the guts for the v6 88-92 temp guages that are not needed anymore for unknown reasons let me know, I'll buy them from you at a reasonable price or donations are accepted. I'd dig into my own stuff but it's my daily driver and can't be without a cluster for too long.

theMonch

Some really great research here. Thanks for posting. I just took apart the '97 T100 cluster I have sitting from my donor to see what it consisted of. It looks to have the zener diode and the resistor that is mentioned in the links I had posted about the gauge mod. I also had a temp gauge like in your pictures that is from a non-SR5 cluster that has the two contacts. I figure that the two contact gauge is too dissimilar to mod up and make work so I am going to take a look at the SR5 gauge like you have shown here.

My gameplan is to use similar components that the '97 T100 gauge uses and "re-build" the '88 SR5 gauge with them. From my understanding it is only the two components that dictate the range, sweep, etc. of the gauge. I probably will substitute the zener diode with a standard diode or resistor to eliminate the "flat-spot" in the gauge while I'm in there.

Looks like your gameplan is similar and you'll probably be beating me to it.

theMonch

Make any headway on what components you are going to transplant? My gauge has started reacting differently now that I have all of the air burped out of the system. It jumps right up to center "normal position" when the key is turned and the engine is started cold. it then sits there and never moves until operating temp reaches 180 then it buries itself on overheat.

Just thought this might help.

77RogueRunner

Not as of yet. I talked to that guy I worked with earlier this week and his wife was at some electronics convention in SF. I believe she got home last night. I'm going over to his house tomorrow and meeting up with her. I have pics and a rudementery circuit diagram I drew up for her to look at. I'm still needing a donor gauge so I don't have to be without mine, and in case I screw something up. I'm going to post over in the classified section to see if I can round one up over there.
My gauge jumps too sometimes. Usually a tap of the cluster trim knocks it back down...other times it works like a regular gauge. Weird thing about your's though is it sounds like it's just seeing the upper spectrum of the gauge. That's something I'll adress with her also....D

theMonch

What are the stripe colors on that resistor? It looks like violet,green,black,gold?

theMonch

I did a little hands-on of my own tonight and removed the temp gauge from my 88 SR5 cluster. Although the main resistors are different in size between it and the 97 T100 gauge, they appear to be identical in functionality. Both appear to be 75 Ohm +/- 5%. (I confirmed this with a multimeter) This coupled with the fact that the zener diodes also appear to be identical (atleast in size and color, etc.) that the gauge should have no problem functioning after the swap.

The only problem with this theory, is that mine is not. Mine definetly was working flawlessly for 22 years before the swap, and afterwards started acting differently.

It now seems to pick and choose if it is going to stick around the middle like normal, or bury itself on overheat randomly. It seems to pop back and forth between these two readings while driving. I now think that something else has to be to blame.

I removed the resistor from the '97 gauge and retrofitted it into the '88 gauge and same results.

I am using an ODBII gauge that reads from the ECM, so I can monitor temp to make sure things are staying cool and also to confirm what the ECM is "seeing". It appears that the sender is funtioning normally.

I am now lost as how to proceed.

How about you Taco? any progress on your front?

UKrunner

Without seeing a schematic, I'm going to take a chance and say that zener is not responsible for a "dead zone" before the gauge reads a temperature.

What a zener diode does is conduct electricity until its zener voltage is reached then it will not conduct any more. So, if that zener diode is say 14.1V, that gauge will never see more than 14.1V at its terminals. This is to protect it from over voltage and over current.

77RogueRunner

Some progress. I talked to that lady, she took my rudementary diagram to work to run it by some other techs that are more familiar with actual moving parts, like the gauge, and not just schematics. I ran some resistance tests with a new digital temp probe. Here are the results for the temps to 212. Temp/Ohms...
130/228, 140/196, 150/165, 160/128, 170/106, 180/86, 190/72, 200/58, 212/50. Here is a pic plotting the curve..



After I plotted this out, I went to RS to pick up a variety of 1 watt resistors. There is basically 100 ohm difference between where my gauge starts and stops. I'm gonna try to put one of those resistors inline with the sender to see if I can't make the gauge start at 165 instead of 125. When I was at RS looking through the bin of component parts I noticed some Zener diodes. 5.1v and 12v. I thought to myself, if ths temp gauge is really just an elaborate volt meter and say 0 volts is nothing and 12 volts is red, then a 5.1 zener diode would stop the temp gauge at a little under half-way....what we're basically seeing when at normal op temp. UKrunner, you are correct, the zener is not creating a dead zone before the gauge reads, it's stopping the gauge from reading any higher temps. I think there are only a limited number of degrees the gauge can "sweep" across regardless of the temp. I'd just rather my gauge come on at 160, sit in the middle at 200 and get red when it's really red. I'd think (hypothetically) if we could trick the gauge into seeing the full sweep and middle is 200 then hot would be 400. Even if that was the case, we are limited by the sender which is progressive and not linear in nature, so the ohm drop gets less and less the hotter it gets. I think that the zener can be removed and replaced with a jumper without any ill effects, then the resistor on-board would have to be changed to one that placed 200 in the middle. It's been a week and I'm going to get back in touch with that lady and run some stuff by her and hopefully she'll do the same for me. Monch, have you tested the resistance at your terminals on your cluster to make sure your gauge is good?

theMonch

No, I have not tested the resistance at the terminals, but I did test it on the individual resistors when they were both out. One was 72 Ohm and the other was 73 Ohm, which leads me to believe they are both 75 Ohm with the +/- 5% tolerance.

How were you testing your gauge? did you just check resistance across the two terminal that the resistor connects? Can the gauge needle be moved to view the changes in resistance?

I put my '88 gauge back in and I havent replaced the 97 gauges' resistor yet, so I can't really check this till next time I pull it out.

The main difference that concerns me is that the '88 3.0 had a seperate sensor that was for the gauge alone and a seperate sensor for ECM functions and a third that exclusively controlled the cold start injector. The '97 3.4 uses one for both the gauge and the ECM and has no cold start injector.

As you can guess I by no means am an electrical engineer, but I do have a slight grasp of electronic components. I would love to have the gauge functioning, but I don't think it's going to be me that is going to crack this thing.

77RogueRunner

Monch, use the FSM snip I posted previously in this thread to test your gauge. The snip with the cluster drawing is the one you want. You said 22 years no problems so maybe your sender is bad. X-reference the values I posted against yours, or buy a new one for about 15.00 to be absolutely sure. The (2003) 5VZ-FE uses 2 coolant senders, one for the ECM and one for the gauge (ECM located in front part of engine, gauge in back part). I can't imagine your 97 5VZ-FE being different..here's a snip of the FSM locations for the senders and such (w/out ECTS is same)...



The gauge sender looks like this..


The ECM sender like this....



I believe the cold start functions are now controlled through the Engine Coolant Temp Sensor, and maybe the MAF. I'll post some more info after I talk to Peggy and hopefully get this worked out...D

UKrunner

Typically a gauge of this sort is a bi-metallic strip with a piece of wire wrapped around it. As the voltage increases, the current thus temperature through the wire increases making the bi metallic strip expand. Your needle is on the end of this strip. So the resistance of the gauge itself does vary but only slightly. If you want to make this adjustable why dont you add a potentiometer in place of the resistor? That way you can calibrate the gauge. You can also get a reading of what voltage is full on red too.

77RogueRunner

UKRunner, with all due respect, you're frustrating me. Trying to legitimately figure this out is frustrating enough let alone being an unemployed concrete carpenter with bills. I'm going for the "actual science" aspect of things here and looking for real data that can be applied across a particular niche of swappers (3.4 with an 88 - 8/92 SR5 cluster). The whole bi-metalic strip (non SR5 gauge) is pic'd and has been dealt with earlier in this thread. It is linear and has nothing to do with the tach cluster that has the zener diode with the dead spot. Not only that, I can't see how you'd mount a potentiometer in the limited space the cluster inards provide. The SR5 gauge is a whole different ball game....again, see previous pics and you will see an obvious difference in the anatomy of the gauges. I'm not trying to come off as an ass but to me this is kinda a serious deal and hopefully someday if I (or anybody else) can figure it out our group of swappers can prevent a major bill in the future cause Toyota decided to go down the "don't bother us" road. By the way, couldn't get a hold of Peggy, gonna try again tomorrow...D

theMonch

Alright Taco I think your onto something there! I just confirmed that my 97 also has a seperate sender for the gauge as well. It was in my component locations diagram as well as I just visually confimed it. (I kind of remember plugging it in now when I refitted the engine harness)

I have been going on the assumption that the OBDII temp data I was reading from the ECM's sender was good, so therefore it has to be something from the ECM to the gauge or the gauges ability to read that signal. Now I know this not to be true and the gauge reads from it's own sender.

I did confirm that the '97 gauge/sender setup worked on the donor prior to removal, so I dont think there is anything wrong with the sender itself, it is just operating on a different scale than the SR5 early gauge cluster temp gauge is.

I just pulled the 3.0 sender out to inspect it. Here is a pict of it. It has 16mm x 1.5 threading.

Taco, do you know if the 5VZ sender mounting boss is the same 16mm? If so it should be a simple sender change that will rectify the problem for both of us I would think.

If it is not the 16mm x1.5, do you know what it is?

Is your 3.0 sender the 16mm x1.5 as well?