Temp gauge q's????

[m1marty]

My temp gauge has been showing a bit low in my 86. By low I mean only onto the line to the right of "C" while driving and it takes a bit to get there. If I let it sit and idle, or do a lot of slow driving while in EL it will get into the middle......and the cooling fan will click on. I thought maybe the sender was bad as I grounded the connector and it went all the way over as it should. I bought a new sender and same deal. The PS gave me a small thin sender and it turned out to be wrong (I have the large 16mm sender) He grabbed one for an 85 and it was right. He said for an 86 it should be the smaller of the two according to his book? Any ideas why the gauge wont read right? Could I have an air pocket not allowing coolant to fully get around it? I have not changed the thermostat yet, but I don't think it is stuck open. Kinda stumped at this one.

[splatterdog]

My 84 did the same thing because the wire was nearly corroded all the way thru right at the sender connector crimp.

[Petros]

I would suspect the t-stat, even if it is fairly new. I had a good working one that kept the temp in the middle third, it eventually failed and I put a new one it, That one always ran to the hot side, and then it went bad too in less than a year. I bought the best one the parts store had, it works but keeps it just above the cold peg, and it is hard to get much heat out of the heater in the winter. This is the same experience I have had with our other cars too. Too many junk after market parts available, do not assume a new t-stat is any good. Take it outand test it with a pan of hot water on your stove and a thermometer, if there is any question get another one.

As far as your sender goes there are two possible causes for the wrong year, either a previous owner swapped out the engine with another used from from an older model, or you got the transition model the year it was changed over. Often they change the vendor of the parts and simply use up the existing stock and switch then. You need more detailed records to know what production number they actually changed to the newer sender. I have seen this a number of times, where the same year Tercel had different wire bundles, connectors and slightly different electrical components installed. The parts books usually are not detailed enough to tell you when the change over actually occurred.

Good luck

[4wdchico]

I prefer not to guess what temp my engine is running. So I have a cheap non-contact thermometer from Harbor Freight. If you are going to be checking the water outlet neck on a tercel, put a bit of masking tape on the outlet and read that with the instrument. Shiny surfaces can read a fair amount off with this kind of thermometer and the tape will fix that.

I will only use real 'yota thermostats in any A series engine. The cooling system is not like a standard one at all with respect to coolant flow relative to the t'stat. Get your hands on a real stock 'yota t'stat for one of these beasties and you will see immediately what I'm talking about.

I change my coolant every year using prestone, distilled h20 & Napa (Wix) Cool. I go two years max on a t'stat in any of my vehicles. I have seen too many t'stats fail and cook an engine to risk leaving one in any longer.

BTW: these engines usually purge air really well, especially with the stock t'stat clocked so the little air bleeder valve is as high as possible.

[m1marty]

I'll stop by the 'yota stealership after work tomorrow and pick one up. I'll also redo the connector and see if that helps. If the gauge still pegs with the conn. shorted out, shouldn't it still read correctly off the sender? It seems as if the gauge is reading 45* off (not 45* temp wise, 45* sweep wise if that makes sense) On the line to the right of "C" would be the midrange (it stays here while driving) and the midrange is actualy the upper range as shown on the gauge, hence the fan clicking on.

[splatterdog]

The temp sender is a thermistor. Resistance chages with temp. ANY additional resistance will throw off your gage. Your connector straight to ground only needs 15-20 ohms to peg the gauge. My point here is, a wire half corroded thru can still peg the gauge when grounded but not flow enough current to lift your needle to where it should be when hooked up . On all 3 I've had that's at/on the bottom of the temp symbol in the middle.

Since you didn't complain of lack of heat and the fact that the fan will come on raises some doubt about a bad stat. If it's of unknown age/quality it would be good maintenance item though.

A thermometer then a multimeter would figure this out for you if available.

I had to cut 5-6 inches off of my sender lead to get to good wire. Solder and shrink tube your connections too.

Good luck!

[m1marty]

I will repair/replace the wire today. Now that I think about it- that makes pefect sense. I just need to remember to sometimes think of the easiest/most obvious thing and then go from there, lol. I am going to replace the t-stat as part of my PM routine. Thanks again.
Aaron

[m1marty]

Update-
Cleaned the conn. and stripped the wire back to were it was clean and shiny. I then soldered the wire and made sure it was good and tight. I let it warm up and.....the fan turned on at the half way point and it didn't go any higher.
This leads me to believe there may be a break in the wire somewhere or maybe the motor was replaced and the gauge is set to use the smaller sender. I may just get a seperate oil press./water temp set up or do the SR5 dash from an 84 out of the JY and see if that helps. Either way I want to do an oil press. gauge. Back to the drawing board I guess.

[Neu]

so..the fan turns on when it gets halfway up the tempgauge? Mine does the same thing..that's what it's supposed to do.

[m1marty]

so..the fan turns on when it gets halfway up the tempgauge? Mine does the same thing..that's what it's supposed to do.

Hhmmmm. I ASSumed the fan wouldn't cycle until closer to the top end of the gauge. If that's the case, now I need to figure out why my avg. running temp is only on the line next to "C". That seems a little cool, but come to think of it both my AE86 Corollas ran that way too. Heat out put is good, hoses are good and hot after running it sooooooo. Maybe I'm just being anal about the whole thing but I am used to a car that goes dead middle of the gauge and stays there unless under heavy load/sustained high speed hijinks.

[Neu]

sounds like the gauge is working, so i wouldn't be worried. Just keep an eye on it, if it starts going above half then you know something might be amiss, pull over and check!

i've ran mine very, very hot before and it didn't hurt.

[splatterdog]

i've ran mine very, very hot before and it didn't hurt.

My 84 has suffered a couple thermal events unscathed as well. First when the rad fan died and I didn't know it yet. Second time related to the bad fan as well. I had told the wife to run the heater blower on high when at low/no speeds. This method got me thru the end of summer and into the fall. Well I should have told her to set the temp to hot too. She got stuck in a long line at the bank drive thru and bubbled all the paint of the rad tank!

Once she was fully trained in on this method it made it thru the winter this way no prob. It wasn't getting much mileage put on it at that point so the inconvenience was minimal.

OK back to the topic- Get a thermometer! The cheap noncontact at harbor freight would be great. You would use it elsewhere too. If the gage is working but off a little just calibrate yourself to the car. Old cars usually come with a trick or two. haha

[takza]

OK back to the topic- Get a thermometer! The cheap noncontact at harbor freight would be great. You would use it elsewhere too. If the gage is working but off a little just calibrate yourself to the car. Old cars usually come with a trick or two. haha

Got one of those. I use it for a lot of things. Can't say how accurate it is...but it's consistent within +_ 1F or so.

Still say that too much overheating leads to trouble down the line...stresses the gasket and the head. I've used the heater method in the desert to get up hills. I hate fixing things that didn't need to be broken.

[Neu]

just remember the laser thermometer's get less accurate the further away you are. Withing like 10 feet they are pretty accurate, but more than that and it's getting dodgy.

[pantah]

My 84 did the same thing because the wire was nearly corroded all the way thru right at the sender connector crimp.

I have the opposite problem. I get a reading on a cold engine not running that has sat overnight at the midrange of the gauge. It looks like I have a unintentional ground somewhere between the sender and the gauge. A few weeks ago I noticed something fishy as the temp would get sometimes get very high on the gauge, but wouldn't trigger the high water temp warning light and the motor didn't seem to be overly hot.

I have two questions:

Where would the most likely place for the unintentional ground to take place?

Where on the gauge or what temp triggers the high water temp warning light?

Note: disconnecting the lead to the temp sender or grounding it out has no effect on the gauge reading.