Co_94_PU

iTrader: (-1)

it is past beer thirty and I shouldn't be responding.

1 indicates out of range, out of range means higher than the setting) so it was more than 200ohms. You have two out of ranges OL(open) and "1" (ohms out of range high). What you would see with one ohm is 1.0 (essentially it will always have significant digits).

Just to be clear you want the wire disconnected from the sender when you do the inspection of the temp sender, otherwise it reads wrong (path to ground from the dash). You also want to make sure your probe has a good bite into the housing of the sender (this is one place you'll find fault with the harbor freight stuff compared to a fluke meter, flukes are very hard and sharp compared to the cheep stuff). Compare the resistance of the ground/body of the sensor to the ground of the intake (this isn't fool proof due to not a lot of current flow) it may indicate time to clean the threads.

Scott Azbell

I just tested my temp sensor the other day and per my factory engine manual and it had me ohm out the two connector pins. Mine is an 81 and a diesel, but it had a great graph for the temp/ohm ranges and was spot on.

881stgen

Picked up a 3.4w bulb and hooked it up per the manual and the needle went right to normal and the light lit up. The manual says if results aren't as expected then test the actual gauge but since they are as expected I guess my next step is to pull the sensor, clean it and test it. I was getting a false reading before when I tested the resistance. I made sure I got a good connection and each time it gave me different readings. Usually in the 40-75 ohm range. I'll report back when I get it cleaned and tested and I will clean the threads as well.

RAD4Runner

Good job!

IslandRET

Griswald,

I had a similar problem with my 87 that wound up being the cheap thermostat that a previous owner had installed.
I verified that the gauge was reading correctly by using a harbor freight non-contact thermometer https://www.harborfreight.com/non-co...ter-93983.html (it should be around 180-190 degree coolant temp when gauge is in middle of range).
I bought a Toyota thermostat (part # 90916-03070 - about $40 on Amazon - $48 at my dealer) and the issue went away.
Toyota uses two stage thermostats ( they have two temperature valves - one large and one small) which helps to partly explain why they are 3X the price of the cheap ones at the parts store.
The two stage thermostat was designed to minimize the temperature spikes we can experience with the single stage units.
If you replace your thermostat, be sure to spend the extra few dollars on the gasket part # 16341-35010 (I didn't think of it and had to wait for it to come). The gasket seals the housing (don't use any gasket sealer, just the new gasket).

Griswald

You know it may just be that simple and that I am over thinking it. I put in a new OEM single stage thermostat last year when I replaced the engine and a bunch of other parts.
I do notice that if I let my truck warm up a while before driving it, it doesn't fluctuate as much.
I may swap in the dual stage you suggested, and see if that fixes it.

thanks for the advice.

IslandRET

My pleasure!
You can Google '1987 Toyota 4runner temperature overshoot' and see if the symptoms are consistent with yours.
That's how I learned about the 2 stage thermostats that were made to correct the issue.
They reference 85 model 22REs, but I found several posts in multiple forums where people had the same temperature overshoot issue that was resolved with a 2 stage T'stat.

Griswald

Hey Island RET, I just installed the 2 stage thermo you recommended and it seems to have resolved the problem!
It doesn't get above 1/2 way mark anymore. I still get a bit of fluctuation, kind of hovers between 1/3 and 1/2.
But so much better! I am going to save the single stage as a spare. How long can I expect the new thermostat to last?
THANKS

IslandRET

I'll check and post info from FSM this evening. From my experience, I'd say to check it every time you do a coolant flush and fill. You should be able to get at least 50k miles from one if engine is well maintained.

Glad to hear your temps are back where they should be!

Tony

IslandRET

According to the 1984 and 1988 FSMs, the coolant should be replaced at 60k miles and every 30k miles after that.
The thermostat should be tested when coolant is replaced or there are any temperature issues like you experienced.

To test the thermosthermostat:
Immerse it in water and heat it slowly.
​​​​​​Large valve should open at 86-90 degrees C (187-194 degrees F).
Valve should lift more than 8 mm at 100 degrees C (212 degrees F or when water boils at sea level).

If out of spec, replace the thermostat.
​​​​Replace gasket any time you install the thermostat.

Tony