Ok at around 150k the gauge starting acting funny and running extremely cool....The next day it threw a check engine light and it ended up being a "coolant temp sensor, engine overcooling"...I had the code cleared thinking it was just not use to the cold weather here in Florida..After all its usually 90 degrees or more here year round and we get one week of cool weather and the car goes all haywire...Thinking it was a fluke none the less...


I flushed the system at 159k myself...Figured it was due and indeed it was. Everyonce in a while it would jump around durning the winter months so i just stopped using the heater till it heated up and it would run fine afterwords

Ok i have a lead foot it seems to me after i drive it fairly hard....like 110 on the interstate the thermostat gets stuck open and the next day it wont heat up right away and takes for ever then once it does it still jumps around...I havent had the cel come back on yet but i was wondering myself if a air bubble in the system could cause this? I reflushed it agian today and it doesnt seem to make a difference the gauge likes to jump around as where im use to it heating up and staying at the middle.... I used a 50/50 mixture of eg coolant both times and even flushed water in the system and let it run in the engine whole nine yards.

I felt the hose on the thermostat side and it has pressure once its heated up and it never over heats just overcools itself at random times....I suppose the sensor could be bad and isnt much in price and not very hard to change...Just wondering if bubbles in the system could cause this false reading? Do these sensor go bad?

All in all 60 70$ and I could replace the sensor and thermostat and hope for the best....

Theres no oil in the coolant or vice versa...Ive never had this problem till the past 10k....gah help
Thanks

 

Air bubbles could cause this but why now, air will bleed out over time. Is the coolant level staying the same over time or dropping slightly.

The coolant system should easily adjust to outside air temperature variations resulting in the gauge staying steady.

Any reason to think the head gasket is blown?

Have you check the wiring and connection to the temp sensor?

How does the gauge operate when the engine is cold.

Heater operation effects the gauge, how so?

 

Well i changed the thermostat cost 17.99 for the best one they had at the part store...When i took out the old one it looked a little bit rusty, put the new one in filled the coolant and my problems have went away...I suppose it was sticking open..

When the engine was cold it would just take forever to heat up, in the winter months i would turn the heater off till it warmed up this was before the flush also, just to get the engine to operating temp. I usually let it warm up before i go anywhere but sometimes i just start it up and im easy on the throttle till its warmed up. Before if i turned the heater on it would drop the gauge back down in these cooler months and i didnt want another check engine light, i suppose i was just prolonging what i didnt wanna do :P

I did take a look at the wiring on the sensor and it was ok, didnt check voltage etc. I figured maybe a bubble was the cause. On my way to work the next morning it wouldnt heat up fully till i came to a stop then drop back down when i started acceleration. Which i took as a thermostat. It only recently started the past 100 miles where it was getting more and more noticable. The coolant level has never really dropped that much till after 100k or so id have to add half a bottle of drinking water every 10,000 miles? i take that as the coolant being time to change however, i did alot of idle time when i 1st bought the car at 40k....I havent noticed any change in coolant level however since i flushed it.

All is fine now though however 18$ later and 10mins of labor and shes fine...I love toyota's! 18$ and 160k not bad i suppose. I mean other than the regular oil changes, brakes, tires, plugs, tranmission fluid, filters etc. Well i suppose you can add 15$ x 2 for 2 gallons of antifreeze.....None the less im happy maybe ill get another 150k

Thanks for the help though

 

it sound like a minor problem but the way to tell the problem its seem to be serious, I have similar problem a few differences but its done after bring it to mechanic...

 

It wasnt to serious i suppose....I just wondering if toyomoho whom has a vast knowledge with toyota's it would seem ran into sensor failures often with the problem I was having or what not. I suppose it could be serious if the thermostat stuck closed and cause and overheating issue. Lucky for me that wasnt the case it was just the opposite.


All is fixed ran it hard today and was just fine...