Thermometer Retrofit Write Up

We all know that many (but not all) 3rd gens came from factory without a way to view the outside temperature. This mod will allow you to add a digital thermometer that won't look out of place in the interior.


The result

Choosing the Thermometer
One of the hardest parts was finding the correct thermometer. Because the display has to be small in order to work, most digital thermometers sold online were too big, those that were the right size either didn't use green LED or had a poor temperature range (only went down to freezing).

I ended up buying my thermometer from someone in Germany, I ordered 2 with a 5m long cable (if anyone wants to buy the extra off me PM me). You can buy it from ebay here, but the shipping is a little pricey. I'll link an alternative in the end. Also it displays in Celsius only if that matters, very few small digital thermometers output in Fahrenheit.

I chose this one because it had green LED, it has a sufficiently wide range of temperatures, had a 5m cable, and it fit within the dimensions. If your going to mount it in the blank panel, the thermometer must be under 40x30mm or else it wont fit within the blank. I also strongly recommend buying a thermometer with a 5m long cord.

Mounting the Thermometer
To mount this thermometer you will have to cut out a hole in the plastic blank. If you use the thermometer I linked you will want a hole that is 20 mm tall and 38 mm wide, expect some minor filing to get it to snap in perfectly.


Some of the tools that were used, plus the piece of plastic that was cut out


To cut out the window I used basic hand tools, the most useful was the pocket knife, the xacto pointed blade, and a hack saw blade I cut down. I tried using heat to help cut through the plastic, but it didn't help all that much. Power tools can be used, but I didn't have any.

The thermometer should fit into the window very snugly, you don't want to risk removing too much plastic. If the window is slightly too small, use a jeweler file to remove small amounts of material. This part of the job took the longest, probably 2 hours with the sparse tools I had.

Installing and Electrical
Before you start soldering, crimping, and cutting, test that your thermometers works. Hook it up across a power source and check that the all the LED in the display work and that its reading is accurate. One of mine was defective (bad LED), the seller is decent and they shipped me a replacement one.

The digital thermometers need power to work (duh), most thermometers have 2 TINY gauge wires coming out the back to provide power. These wires are small, delicate, and short. You'll need to solder on some thicker gauge wire to the end for mounting in the vehicle. I recommend using wire no larger than 16 gauge.

I originally intended to power this by filling a blank spot in my oem fuse box, the problem with this was the thermometer would not turn off when the vehicle was off.

I grudgingly ended up using fuse taps, this method is the easiest to do. It isn't pretty though, and your relying that Toyota's safety margins will allow for the additional load from the fuse tap.


Messy fuse box, ignore the right fuse tap, that is for something else

The other wire that isn't in the fuse tap, is the negative wire that is normally black. This is easier, crimp a ring terminal to the end of the wire and screw it into a ground point. I used a ground point that was in the upper left part of the footwell.

I think the result is worth the messy fuse box:


Thermometer Sensor Mounting
This is the last only step that I haven't done. My plan is to run the cable along the driver side through a vent that is in the cargo area. Toyota sells a version of this vent (PN 62940-35020) with a built in grommet, currently it's on backorder which is why I haven't finished with this step.

If you want to mount it in the same place, it's essential that you have 5 meters of cable. The pressure vent that is our 4runner's also doesn't have the built in grommet, you have to buy the part I listed. And you have to buy the grommet for it separately.

However, there are a variety of places that are suitable for the sensor, just make sure it isn't affected by engine or exhaust heat, and is in a sheltered place.

(Edit 6/17)

Section of cable run at the rear door

Here are some more photos of the cable run. I ran it under the door sills to the back, from there I poked the cable under the plastic panel that is by the wheel well.

Dust that greeted me once I removed the vent

I had to remove the driver bumper cap (simple really) and the plastic bumper top to get access to the vent. It's a good thing I'm replacing this, the rubber flap fell off when I removed the bumper. It was brittle like uncooked pasta and it had let a bunch of dust inside.

Temporary setup, the silver cylinder is the thermometer probe

Because my part still isn't in, the photos above are of my temporary setup. I used a washer to keep the probe from going back through the air vent, there isn't a flap there anymore

I'll update this section when I finish mounting the sensor.

(Update 1/9/2023):
I ended up not sticking with the location I chose initially. I had to move it to the complete opposite end of the vehicle.

I didn't think the engine heat would register if the probe was located on the side of the vehicle far away from the engine. But the engine heat would raise the temperature significantly and make the thermometer give higher than ambient temperature readings.

Read about it here and heed this warning. If you mount it where I ended up relocating the sensor (behind the front grille) to, you'll be alright and it will work perfectly.

(end of update)

Relevant Links and Extras
Link to project photo album (Broken/Replaced)

Link to project photo album part 2
(Broken/Replaced)

Link to stable photo album (part 1 and 2). I had to replace all photos made on my posts because Imgur removed all content made without an account. Every description is painstakingly preserved from the original post.

Link to thermometer I used. I bought the "grun" color display with 5 meters of cable and (PM me if you want to buy my extra one)

Suitable alternative if you don't care about having a narrow temp range

Air vent with grommet part number- 62940-35020

Nice write up!

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Good job. Looks good in the rig.

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That’s where I mounted my Alt amp output meter.


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Well done.
The thermo couple for OE outside temp is attached behind front bumper leftside turn signal area could be alternate location.

Cool write up! The rear pressure vent 62940-35020 doesn’t come with a grommet. It comes with an empty hole where you can put a grommet though. I have one that I ordered but haven’t installed yet because it requires rear bumper removal to get to it.

Edit: Here’s a link to a wiring grommet you can use with the rear pressure vent. Amazon.com: Daystar, Universal Firewall Boot, Single, Accommodates 3/8" to 1" Diameter Wire Bundles, fits any vehicle that needs a wire loom, KU20040BK, Made in America , Black : Automotive

Very nice! I did something similar, but put the gauge in the dash bezel. Much more work than your approach though - https://www.toyota-4runner.org/3rd-...temperature-voltmeter-gauges.html#post2986294



I'm still hoping to find a digital Fahrenheit gauge to replace my Celsius one, but as you found out, those seem to be impossible to come by.

How about a cabin temp install this needs a better look to it. Not really, just checking.

Your right about the grommet Bad Luck. I purchased some from autozone. That vent is really backordered, I wont get it for over a month.

I'm fine with the thermometer being in Celsius, I hope to live abroad and being forced to use it might help me adjust to that unit.

Spiker Engineering said:

I'm still hoping to find a digital Fahrenheit gauge to replace my Celsius one, but as you found out, those seem to be impossible to come by.

Click to expand...

This is the one I used:

PEMENOL 12V Red Fahrenheit Digital Temperature Meter -76F~999F LED Display with Industrial Grade 0.5m K-Type Thermocouple Temperature Sensor M6: Amazon.com: Industrial & Scientific

There are a few options for Fahrenheit, but definitely a little harder to find than Celsius.

I put mine down by the shifter (next to my stereotypically placed trans temp gauge)

I finally got my air vent from Toyota today, my dealership got one of the last few in the country (from Chicago) rather than wait indefinitely for Toyota to make more.

I should of read my own thread more thoroughly because Bad Luck commented that the grommet size was 38-39mm in diameter.

My temporary setup has for the most part worked, but I might have to tweak the placement. I've noticed on long drives that the engine heat will be picked up by the thermometer, leading to readings that far exceed the actual temperature (by as much as 10C above).

I wonder how far the air temperature of the intake is off from the ambient air temperature?


If it's really close another method would be to pull that temperature out of ecm and display it on a screen with an application like torque pro. As that is how I plan to get most of my engine vitals by using an android head unit. So I would have the backup camera as well. I would wire it so it only connects when the ignition is on connects to the obd 2 connector to get all it can that way. Thus only needing a few other sensors to monitor everything on a 3rd gen.

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I imagine that the air temperature from the intake is a few degrees warmer, but as long as it isn't too far behind the engine the radiant heat wont affect the probe.

I don't know how I'm going to fix my problem, moving the probe up and out of the way would be good, but there isn't a good way to do it. I'm considering adding something to redirect fresh air to the probe while keeping the hot engine air away. The 5m of cable gives isn't completely used, so I could move it around the back.

Pyral said:

I imagine that the air temperature from the intake is a few degrees warmer, but as long as it isn't too far behind the engine the radiant heat wont affect the probe.

I don't know how I'm going to fix my problem, moving the probe up and out of the way would be good, but there isn't a good way to do it. I'm considering adding something to redirect fresh air to the probe while keeping the hot engine air away. The 5m of cable gives isn't completely used, so I could move it around the back.

Click to expand...

You’d probably get the best result putting the probe in the front bumper where Toyota put theirs. You’ll probably get some heat soak when stopped for a little bit, but not too much.

Could very well be a few degrees off. I never checked.

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I played around with placement of the probe quite a bit, to reduce soak back when stopped (never had soak back when moving). The best location seems to be right behind the grille. While you would think that the radiator soak back would affect the readings, the forced air flow from the fan apparently offsets that.

Every other location I tried, including behind the truck and at the air intake, had more soak back.

I only saw soak back when stopped, it was never an issue while moving. I suppose you would see soak back while moving if you have the probe mounted in an area that sees almost no airflow.

brillo_76 said:

Could very well be a few degrees off. I never checked.

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Click to expand...

Ambient temp on my drive to work was 80 degrees this morning. Intake temps fluctuated between 5-15 degrees above that once the engine reached operating temperature. My commute is 7.5 miles and takes about 15 minutes with half of the miles at 65 mph.

Winter Update

I've had this on for 5 months now (feels like ages ago) and a few updates.

Everything works perfectly, but after keeping the location of the probe at the side air vent, I do NOT recommend it. It can affect the reading by as much as 10 degrees C, and no matter the conditions the engine raises the temperature. It will only give an accurate reading a when you start the car.

I plan to move it when I replace my stripped power antenna motor late this year early next year. I'm thinking behind the side marker light because it's fairly sheltered and should get a good flow of fresh air. I'll update this thread when I do so.

For those of you in the North concerned about the thermometer I used only going down to -10 C (14 F), I've found that it can actually read at least down to -15 C (5 F), and I bet it can go lower. I'm not sure why the seller said it's limited to -10 C.

Bonus photo of some snow trekking

Finale

TL;DR: Put the thermometer probe in front of the engine. The cable is rather small so armor it and keep it sheltered as much as possible (unless its the sensor itself).

This is a continuation of what is already on this thread. If you want to understand why and how I got here read my earlier posts.

Over the holidays I moved the thermometer sensor from the rear of the vehicle to the very front. This task was not helped by the fact that the previous owner had sealed the grommet on the driver side fire wall. But I was also replacing my power antenna motor, so I used that grommet. If your doing this use the grommet on the drivers side.

Of course I had the essential items before I began:


The power antenna grommet is in the passenger foot well and it exits to inside the fender where the antenna resides (photo 1 & 2). From there I routed the cable through another hole used by the rear window fluid hose to get into the engine bay. From there it was simple to route it to the front of the vehicle.

1
2(the thinner cable belongs to the thermometer)

It's important to make sure the cable is protected, especially where it's exposed. My preferred style of cable protection is to use tubing with a slice running down the length of it so I can press the cable in. You can use whatever you want. I used a variety of tubing types to armor the cable.

Even with my extremely indirect cable path, I still had extra cable at the end. Because I used larger diameter hose outside I was able to double up the cable through a section of hose before taping the hose shut. If you use the drivers side grommet (which you should), you wont need as much cable as I originally suggested in my first post.

Mounting the sensor was tricky. It requires a balance of making sure the sensor is sheltered away from harsh elements while maintaining fresh air flow. It's worth noting that I submerged the sensor in flood water without issue, but protecting it is still a good idea. I mounted it behind the front grill on a cross member (3).

3 (the thermometer cable is in the clear hose, the sensor is the silver cylinder)

I took extra care to protect the wire leading into the sensor. I added heat shrink around the lower half of the probe to act as strain relief and prevent degradation from the harsh environment (4). Don't get carried away, you don't want to add so much protection that you insulate the sensor.

4 (the sensor is the silver cylinder)

Finally like all mods that add additional wires, I added a few labels (5).
5

I've driven my vehicle a lot since I did this and it's working how I hoped it would. The thermometer itself is accurate, and it no longer gets affected by engine heat despite being closer to it. Unless something breaks, this will be the last time I mess with this.

Link to the photo album updated