OEM temperature-gauge fault

[FJtimr]

Looking for some help verifying my diagnosis path on a 1987 US-spec FJ60 with the 2F.

Problem: The factory water temp gauge moves into the red after about 20 minutes of driving. The engine does NOT appear to actually be overheating.

Background: The previous owner had installed an aftermarket temperature gauge. That gauge worked properly and showed normal operating temperatures. I'm trying to remove the aftermarket gauge and get the original cluster gauge working again.

So far I have:

• Removed the aftermarket gauge.
• Installed a new temperature sender (part #83420-20020)
• Ran a new wire from the sender to the original OEM temperature-gauge wire.

Result: Factory gauge still gradually climbs into the red zone once the truck is warmed up.

Couple of questions:

1. Is there a diagnostic approach to validate the temp sender is right? Or should I just assume it's good?
2. Are ~90 ohms at 170°F and ~40 ohms at 212°F reasonable values for the correct sender?
3. Is there anything specific in the FJ60 cluster, gauge, voltage regulator, ground, etc. that commonly causes the temp gauge to read progressively too hot?

 

[Mark W]

I can't help you with the specs right now. Nowhere near my FSMs at the moment.

Is your gas gauge acting up too? if so that is a sure sign that the resistor that is supposed to drop the voltage for those two gauges is on the fritz. It is a not REAL common, but not unknown failure point. More juice through the gauge means higher readings.

Mark...

 

[Mark W]

The sending unit *can* go bad. Personally every one that I have encountered failed in such a way that it allowed too much current through (the sending unit grounds the circuit) and this will quickly overhear the thermo coil in the gauge.. likely bend the delicate needle even. THIS results in a gauge the begins to consistently read low and it gets to the point that when the rig is turn off the needle can actually drop out of sight on the low end of the scale.

There may be other failure modes for the sending unit, but I have not encountered them.

Mark...

 

[FJtimr]

Thanks @Mark W the sender is new and when hooked up to the after market temp gauge that reads correct. My gas gauge and the others in the cluster are performing accurately (as can be expected by the limited indicators!).

 

[FJtimr]

Hey @Mark W where is the resistor located for that wire?

 

[klip]

Temp Sending Unit?

forum.ih8mud.com

I don’t know how to link, but copy and paste that. It’s pretty common. A lot of info in that thread.

 

[klip]

Oh wow I guess I do! Btw, I googled F60 temp gauge pegged and looked for the ih8mud links. Found it pretty quick. Google works good for that.

 

[FJtimr]

Thanks @klip huge help with the link! Thank you, good reading for tonight!

 

[Lead Head]

Is the sender from a dealer?

What's "normal" operating temperature to you? These engines run pretty steadily around 185-190F. Getting close to 205-210 (which is well before it boils) will have the gauge near or in the red.

Where does the needle rest with the key off?

 

[Spike Strip]

It's not a Resistor - it's the very crude small Voltage Regulator in the fuel gauge the shares a signal ground with the Temp gauge.

This is (was) a very good thread (in the FAQ) about the problem. Unfortunately, most of the hot-linked pictures have disappeared.

@Spook50 was working on a fix, but I don't think it will happen ?

Best remedy is to install a QUALITY aftermarket Temp gauge with a sender in the upper radiator hose or one of the BVSV ports if you're desmoged.

L

Thread 'Temp Sending Unit?'

Nov 28, 2004

The 62's temp guage was acting strange the other night. I was on a 30 mile drive in 40 degree weather. Guage read normal through the "warm up" the first few miles. I then noticed that is was fluctuating in a weird manner. It is normally rock solid after warm up no matter if it is winter, summer, up hill or down. But this time is would move up toward the "red zone" quickly then back down in a matter of say 5-10 seconds. This seems way too fast to be an accurate reading. I have seen sending units react to air bubbles in this manner, but I checked the system and found it to be full and...

• LifeIsGood
• Replies: 109
• Forum: 60-Series Wagons

 

[FJtimr]

@klip wow, that’s a read but incredibly helpful. That’s a couple of chapters that should bdd Ed published!

@Lead Head the part is Toyota OEM.
Normal operating temp is usually around 182.
Key off at rest is just below the C mark, in the black are (not white markings).

@Spike Strip thanks for all the comments in the aforementioned post, super helpful.

Next steps: (before going back to the aftermarket gauge reinstall!) clean battery terminal and ground, clean fuel gauge points. Install new “old” OEM gauge.

Not sure I’ll go the in-line resistor unless it’s a simple install splice into the wire out of the sender.
I’ll circle back with my next results. You guys are awesome, thanks so much.

 

[Spike Strip]

This was done by the PO of my 60. It was something Richard at K&H Land Cruiser specialists in Canoga used to routinely do when this phantom overheating issue popped up. Verify, but I think that's a 15 ohm resistor. That G/R wire I believe goes straight to the Temp sender in the head, but check the color coding for your year truck, if you want to do the resistor deal.

I did fix that Genius PO install job for the resistor, btw.

I've have both the aftermarket Autometer and the stock gauge and the stock never goes above 1/3 ish, but the stock gauge just isn't safe because it reacts too slowly. A good mechanical or even electrical aftermarket is much more sensitive.

 

[Godwin]

Reinstall an aftermarket gauge that will give actual temps. I’ve used Autometer gauges in several Cruisers and knowing the actual temps provides solid information instead of the stock gauge guesstimate.