Chet Wesley

Hey,
I just bought this truck, got a good deal on a one-owner 4x4 regular cab pickup. First time owning a Toyota.

Driving it home I realized that the temp gauge was staying down near the C end for the entire 30min drive.

I've searched the forum a bit but in most cases where the engine won't warm up people say the heat doesn't work.

Heater blows hot air. Does that preclude the thermostat, or could thermo still be failed stuck open? It's in the 50's/60's F here.

Thermostat is an easy cheap fix so seems worth a shot, but just wondering what else it might be or if I am barking up the wrong tree.

Don't think the gauge is straight dead because it does show a little warming from dead cold, but never moves more than a sliver of the way towards "H."

Only other hint that may or may not be related is that idle speed fluctuates a little, like quick rising and falling in speed as I just have it sitting there idling, even after driving around for 15 min.

Thanks

CW

Badlander

Thermostats are cheap, so it's worth a shot. It could be the temp sensor too. This sends the reading to your gauge cluster. The sensor is on the manifold between the 2 and 3 cylinders.

Chet Wesley

If it's the temp sensor, then that is just sending a faulty reading to the dash, when actually the vehicle is operating normally? Does that affect any other operation of the vehicle? I thought I read when I was digging through threads that it is a different sensor which the computer uses to inform its regulation, is that correct?

One thing I forgot to mention is that I felt the upper radiator hose and it does feel warm and firm, and the bottom one feels cool.

Odin

At first it sounds like you have a lower temp thermostat than the stock 190-195 but the other description says possible faulty or mismatched temp sending unit.


Since you have good heat and the gauge barely moves it sounds like sending unit to me. Been wrong before though.
It's important that you get that sorted out because you definitely don't want to be running these engines too hot. Head gaskets aren't fun.
I'm sure someone will respond who can help you sort out the sending unit and make sure you have the correct one.


I'd change the thermostat because it's an unknown to you and suspect at this point. By far the most popular one around here is the OEM Toyota P/N: 90916-03070. http://www.lceperformance.com/2-Stag...-p/1032081.htm
It did not come stock on our engines so don't bother looking it up under applications. It's on the expensive side but those who have purchased it love it. There's an aftermarket substitute that one member is using and apparently it's been working fine for him. O'Reilly's or AutoZone PT# 41492 https://www.yotatech.com/forums/f116...mostat-284848/

Make sure you get all the trapped air out of the coolant system because it will play hell with the idle sending the rpm up and down.
If you see rust in there it's a good time to change to the Toyota Red coolant and DISTILLED water. Toyota Coolant PT#002721LLAC01

Badlander

The sending unit to the gauge affects the gauge, so I guess that wouldn't necessarily be a horrible problem. You want to know what temp your engine is running, so it should be replaced if needed. The sensor that talks to the ECU is located in the front off the manifold. You can test these. I believe 22reperformance.com had some video how-tos.

Chet Wesley

Checked that sensor with an ohm meter. It read around 600Ohms when cold, then slowly was dropping till it was about 300 ohms after running a couple minutes. Any idea if there is a chart or something of what it is supposed to read at different temps?

I also tried grounding out the connector and the gauge slowly, in sort of jumping steps, went from C up to H.

So at least on a superficial level, seems like the sensor and gauge are working. Not sure if the sensor is reading appropriate levels, but resistance is changing in response to engine temp.

I suppose I could wire a 1K pot in the middle between connector and ground and move it to see what resistance levels are supposed to correspond to what gauge readings?

Chet Wesley

One more update: after taking readings and reconnecting connector to sensor, went to run an errand in the truck and the heat gauge had completely stopped working. Way to the dead left.

When I got back home, engine good and warm (presumably) I took a reading on the sensor again and at first it was around 350 ohms. I rubbed the probe on the sensor pin a bit in case there was any dirt/corrosion, and suddenly it started reading something around 75-85 ohms.

Plugged it back in and started the truck up and my gauge is reading higher than it was (though still seeming low, maybe around 1/4 of the way up).

So it may just be a case of bad connection or corrosion on the sensor. I'll keep an eye on it.

Badlander

Sounds like you may be onto something. If it is due to corrosion and/or just dirty, you may want to clean or replace your other temp sensors. They may have the same corrosion. You don't want faulty readings going to the ECU.