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Old 07-17-2010, 09:15 AM   #1
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1987 22RE Temp Sensor, Sensor Switch Problems

Well, I am sure that some of you have dealt with this problem either with your own truck or helping others with theirs... I have searched this forum for some answers and have gotten nothing but mixed information. There seems to be no general concensus on which Coolant Temperature Sender/Sensor/or Switch does what on a 22re.

My problem consists of two small problems that I thought would easily be solved. First, I purchased this truck roughly a month ago and am thoroghly enjoying it. I noticed the second day that within 20 seconds of starting the engine cold in the morning, the temp guage in the cluster (SR5 Cluster) would jump from cold to Operating temperature (just below halfway up the guage). I double checked that there was plenty of coolant in the truck, and that I am not overheating. Within a few days I also noticed that when I would turn the key to start the truck in the mid afternoon (I know the engine is warm, but not at operating temp), the guage would jump strait to Op Temp, and I would have a hard time starting the truck, eventually getting to the point of having to step on the gas and crank the motor at the same time.

My research has shown that these two problems could easily be solved with replacing the Temp Sendor/Sensor/Switch...Only question now is which is which. I have discovered possibly four different possibilities to the great question that even the almighty internet seems to have trouble with. I have included pictures to help make things easy...hopefully.

Ok, First, this one was the obvious choice...
Click the image to open in full size.

I removed the harness from the switch, and turned the key, (I did not crank the engine), the guage went strait up to Op Temp. Not the right one...

Next, I looked at this switch, Right along the fuel rail like a lot of people have talked about on the passenger side of the head. I removed the harness and repeated, with same resultes...

Click the image to open in full size.

So here is where I get stuck. I talked to the guys at my Local NAPA (They seem to be fairly competent individuals when it comes to Parts Salesmen). He showed me a third and possible fourth option down below the upper radiator hose where two plugs sit next to each other... One is brown or black depending on who you talk to, and the other is typically green.

Click the image to open in full size.

Close up...
Click the image to open in full size.

Now through my own process of elimination, I have determined that one of these two must be responsible for the guage in the cluster. I have not quite figured out how to remove the harness due to its complexity and my lack of experience. I assume that someone makes a $75 tool to properly remove them...

Anyways, I know this is a long question and I would definately appreciate any help or insight or information that anyone has regarding this situation. Hopefully we can determine exactly what does what and maybe make a sticky for newbies like me who have this problem. Thanks. Ill be checking back in a day or so.
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Last edited by americanmcss; 07-17-2010 at 09:17 AM.
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Old 07-17-2010, 09:27 AM   #2
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The first two pictures you have are temp switches for the ECU, temp #1 is deeper, temp #2 is the one on top of the thermostat housing.

The sender for the gauge is the green connection you have circled in the last picture. You need a screwdriver tool that has a hook on it, unclip that green connector, and slip a deep socket over it to get it off.

You might want to search 'temp gauge overshoot' there's some good information about this issue.

Also, if you download the FSM Here it explains how to test the resistance of this sender gauge, just to see if this sender is in fact causing this issue
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Old 07-17-2010, 09:29 AM   #3
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The problem your having is not really a problem, just about all toyota trucks do this, its called temperature over shoot. Toyota came out with a special thermostat that is supposed to fix this problem. As for your pictures, im not sure what the temp sensor in the first picture is for, the second picture is the temp sensor for the gauge, third picture i can`t tell what you have in the picture, fourth picture is the temp sensor that`s used by the computer to read coolant temperature.
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Old 07-18-2010, 02:03 PM   #4
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Ok so after a little more looking around and checking out the overshoot problem...I would have to say that I dont think that this is what im dealing with. The guage never reads higher than normal operating temperature, and it never reads lower than operating temp when its warm. Just the startup problem...
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Old 07-19-2010, 06:06 AM   #5
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gauge sender is usual on the top of the intake by 2 and 3 cylinders and is your 2nd pic
ECU sender is on front of the intake, green plastic and your 3/4 pic

the other sensor, on top of the thermostat pipe in pic 1 I don't know what its for

Well what you are saying contradicts what PismoJoe has stated, and I think he is right. I tried disconnecting that sensor to turn off my guage and it still read normal temperature.
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Old 08-01-2010, 10:44 AM   #6
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I believe razed is correct. Best answer to temp sensor/switch location I've seen comes from GrimReaper ( http://www.yotatech.com/f116/22re-no-power-96417/ ; reply#6). My understanding is that the issue is with the gauge (in the instrument panel) itself.
The gauge is not linear in response in early 4runners. The factory put resistors in the circuit to dampen the needle (I think to deal with the "temp overshoot" issue, but I could be wrong) so the needle stays in the "cold to normal" range most (too much) of the time. So, at least in older gauges, the needle shoots to low normal, the rises to normal and stays there until the engine is on the verge of overheating, then shoots to hot (fried). With mine, if I hit the dash when its cold, it will sometimes drop to dead cold then rise "normally", sometimes this doesn't work. Unplugging the lead to the sender in the manifold on my 22re does not affect this cold, but will keep the gauge from going to "full" normal when the engine is warm. I do not believe the sender is the problem. I've never seen the temp overshoot issue on my '86. On my '90 p/u, I did see the overshoot issue, but my gauge worked "normally". Others may have better ideas.
There are threads on various forums (maybe YotaTech, I don't remember) to modify the dash gauge to make it more linear. I plan to just get an aftermarket gauge; there apparently a boss (on some early 22re's) on the side of the manifold just below the stock sender location where another sender or the stock one could be mounted if you want to go w/ 2 gauges.
Regarding your symptoms, you may be having problems with the temp sensor for the ecu (pics 3 & 4). If you can't find the specs in the FSM, I think Autozone has an online explanation for testing this sensor.

Last edited by jandyb1; 08-01-2010 at 10:46 AM.
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Old 08-26-2010, 11:22 AM   #7
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Well I managed to solve my guage problem...New after market guage. Easy enough I suppose. I have checked the resistance of the thermostart switch and the temp sender up front under the thermostat housing. One of them is within spec, and the other is not. (cant remember which is which right now.) Oh and for future reference for anyone who wants to know. The sender that is down by the fuel rail is for the guage, and not the one down below therm housing. Still have not been able to solve the starting problem, but Im sure that when it starts getting cold up here, It will become more of a problem and I will start getting serious about it. Thanks for your help everyone.
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Old 08-26-2010, 11:22 AM
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