Temp Gauge

I have an 87 Toyota pickup. Sometimes when I start the truck and start out the temp gauge will show the coolant is already warm/hot. Not red lined, the needle will be at the location where it typically runs when the engine is warm. I will tap the instrument panel and it will drop down where it should be then slowly climb to the right location, like I would expect it to do. I purchased an instrument panel out of a wrecked truck and it did the same thing. I also replaced the sending unit and added an extra ground wire to the gauge thinking I was losing ground. So far none of these things have worked. My father has the same truck and had the same problem. Any one know the fix?

Thanks for the help.
Paul

Boy, you got me stumped, did all the trickes I would have already, just be sure to check for corrosion. By the way is this on every start or just warm starts?


I should would be interested in the soloution to this when you find out
Nate

Natenelsen,
Thanks for the reply. I checked for corrosion, didn't see any. The problem is most noticable at cold starts. For example, when I start out in the morning the gauge will show the engine is up to operating temp seconds after starting the engine or 1/4 mile down the road. Then when I tap on the instrument cluster/panel the needle will drop down to a more reasonable read out. Then it will climb to the operating temp. and it appears to be the proper read out. It doesn't do this every time. Maybe 2 to 3 times out of 10.

Well My next step would be to actually measure the temp of the coolant with a probe, I once had a car that had a sticky t-stat, it would be all clammed and the water around the sensor would get almost too hot (top 1/3rd of temp range) then the t-stat would finnaly open up and let in a flood of cool water from the Radiator, causing the temp to drop below the normaly op temp for a short while.

If you have a good multimeter with a temp probe, use it and then compare that to the gauge on the cluster, Maybe the gauge is correct.

I replaced the thermostat and flushed the coolant system. The system was very clean. I haven't compared the temp of the coolant with another measuring system. However, that wouldn't explain how the temp gauge displays the coolant at operating temp seconds after starting the engine after sitting all night. Then drop down to zero (or ambient temp) after I tap the instrument panel and then climb up as the engine actually does warms up to operating temp.
Am close to installing an after market temp gauge and forget about the OEM gauge.
????

i have the same problem with my 87 pickup, my temp gauge will rise to the operating temp. right after i start it up. i checked the sending unit, and it seems fine, i unplugged the sending unit and i still got a reading, so im thinking either there's a short to ground, or the gauge is faulty. i also tried to remove the gauge and cannot seem to get the black cap off of the gauge, any answers?, greatly appreciated.

I would love to find the solution to this problem, If either of you guys are around the Alabama area I would really like to help you take a look, I would like to see how this turns out.

Nate

My father has a 87 pickup, very similiar to mine and he has had the same problem once or twice.
Jaysheard, have you ever tapped the instrument panel when this occurs?
On my if you tap the instrument panel once or twice it will go down to cold and then slowly rise back up to operating temp, this is at start-up.
I've done the same thing with the sending unit when this occurs with the same results as you had.

either of you guys know how to remove the caps off of the gauges so i can check the temp gauge, or even possibly remove it, and install a new one???, b/c i have a feeling that the gauge is shot. Paul, i have tapped the instrument panel and it does the same thing you experienced, but i don't want tap the panel everytime at start-up, i want a gauge that works!! i've tried to remove the caps but i cannot seem to get them off of the panel and i don't want to crack it. thanks guys

i know this thread is a little old, but i have come to the conclusion, after all the troubleshooting with this, that it is in fact, the temp gauge itself. I just got off the phone with Attrell Toyota in Brampton, so you guys all know, i live in Canada. He gave me a quote for $267.85 for that gauge!!!!!!!! I don't know about all you guys, but that's ridiculous!. Even after the exchange rate and shipping if i were to order that part on an american website, it would still be cheaper than that!! There just giving me the run around, don't get me wrong, tell me what you guys think? Like i was saying in my last post, i dont want to have to tap the panel everytime i start up my truck just to get a "somewhat" accurate reading, which may...or may not be an accurate reading. I just feel that i shouldn't accept the gauge for what it is right now, maybe one day i could be driving down the road, not knowing that my engine is overheating, but i wouldn't know that b/c my gauge is reading incorrectly. Also, can someone plz let me know if there is an easy way of removing the caps over the needle on the gauge, there giving me such a hard time! Please help me, as well as all the others b4 its too late, thanks guys

Jay

greetings again, as i have mentioned in my last post, i found the culprit, the gauge itself!!! i found out why the dealer wanted to charge me lots of $$$. You cannot buy a replacement temp gauge on its own from a dealer. The oil pressure gauge and temp gauge come as one unit, thats why so much dough! I thought that seemed a lil ridiculous considering that if your oil pres. gauge is working fine, and mine is, you have to replace them both no matter what. So i decided, im not paying that much. As i said earlier, I live in Canada.....I went into my local Crappy Tire and purchased a temp gauge from them. NOT a performance gauge i'm assuming. Cost me 13 $CDN, not bad i thought. For any of you guys that want just a simple gauge to tell you the water temp. this one works just fine. I thought I'd test it to see how well calibrated it actually is. I put the sensor in boiling water and came out to bout 98 degrees celsius, and water boils at 100 degrees celsius, so i thought that was quite accurate. If any of you guys want the P/N:34-0120-4. It comes with all the connections: sensor, threads to replace the orig. sending unit, mounting screws. etc... so i will let you all know how it turns out when i install this bad boy in my truck after skool tomorrow.

Jay