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View Full Version : temperature warm when idling, cold when driving??



supra97rx7
03-06-2008, 02:37 AM
i don't know if anyone has noticed over the past months/year or so, but i've been having idle speed troubles and thus, gas mileage issues.

anyway, i was looking through the BGB today when i noticed that i completely forgot about the idle speed adjustment screw.
i went outside, let the car warm up (temp gauge right in the middle), adjusted the idle so that it's at about 800.

next, i went and drove it around the neighborhood. whenever i had to stop and clutch in or go to neutral, i saw something that never happened before - the tach would quickly drop to 1000rpm! amazing! usually, it would drop to about 1800 or so, and SLOWLY drop to 1000, if i was stopped long enough.

i continued driving, and i hit more stop signs. this is where i was becoming sad : (

when i clutched in or went to neutral, RPMs would only drop to 1800, just like before. confused, i look at the temperature gauge - it's at the VERY bottom. not just lower than before, but the lowest it can possibly be.

now, this was in, maybe 20-30 degree weather(?), so i can see that cold air while driving helps cool the engine. but cooling it to the point that the temperature gauge reports extremely cold engine? no, i don't believe the wind has that power. i was just driving around the neighborhood, too.

so does anyone know what's going on? it's killing my gas mileage. the "false" cold reading makes it idle 1000 rpms higher than it should.

thanks.

juggernaut
03-06-2008, 02:47 AM
hmm. the only thing that comes to mind is a stuck thermostat. having your cooling fan short to power couldnt cool it that much, so im out of ideas.

celicaGT90_05
03-06-2008, 03:13 AM
it could be a faulty temp switch or a poor connection

celica9303
03-06-2008, 03:16 AM
T-stat in need of replacement believe it is stuck closed I could be wrong but it definetly sounds like a t-stat problem

supra97rx7
03-06-2008, 03:17 AM
so i kept searching, and in this thread (http://www.celicatech.com/forums/showthread.php?t=31589&highlight=stuck+thermostat), i found the following -
if the the thermostat is stuck open heater will not be hot. but u should notice because your temp gauge will start dropping while the car is moving.
that is aboslutely what's happening. interestingly, the thread is about heater not being warm, but my heater can get very hot (at least, it seems to get very hot to me)
??

edit again: found this (http://www.celicatech.com/forums/showthread.php?t=11452&highlight=stuck+thermostat)
exact same issue. looks like it is the thermostat.
how hard is it to replace?
i looked it up in the BGB, doesn't seem too bad. but me and my dad replaced the alternator on our previa, which shouldn't have been bad at all, but it was a massive pain in the butt.

Blackcloud
03-06-2008, 03:54 AM
mine gets colder as it idles

celicaGT90_05
03-06-2008, 04:08 AM
T-stat in need of replacement believe it is stuck closed I could be wrong but it definetly sounds like a t-stat problem

closed would cause an overheating problem because the water will remain mostly in the motor and wont reach the radiator, open could cause overcooling, but I wasnt sure if it would cool off the engine as drastically as described, which is why I said it was a possible switch issue. It can cause an overcooling condition though which will translate to motor problems

supra97rx7
03-06-2008, 04:16 AM
closed would cause an overheating problem because the water will remain mostly in the motor and wont reach the radiator, open could cause overcooling, but I wasnt sure if it would cool off the engine as drastically as described, which is why I said it was a possible switch issue. It can cause an overcooling condition though which will translate to motor problems

a switch issue? what switch might this be?
or is it definite now that my t-stat is open?

celicaGT90_05
03-06-2008, 04:18 AM
temperature switch, it tells the ecu what the coolant temp is so the car can adjust air/fuel ratios, so as when its warming up. If it thinks its cold, then it will dump in more fuel, which explains it reving higher and using more fuel, but it could still be the t-stat

supra97rx7
03-06-2008, 04:22 AM
where's this temperature switch?

celica91gts
03-06-2008, 04:56 AM
it could be your thermostat. usually they close shut when broken. but there are brands out there (failsafe for example) that will stay open after they stop working. this prevents your car from overheating but it will also take ur car ages to warm up. have you ever changed your thermostat?

supra97rx7
03-06-2008, 05:03 AM
it could be your thermostat. usually they close shut when broken. but there are brands out there (failsafe for example) that will stay open after they stop working. this prevents your car from overheating but it will also take ur car ages to warm up. have you ever changed your thermostat?

we got it in november of 06
ever since having it, we've never changed the thermostat

celica91gts
03-06-2008, 05:08 AM
check your radiator fluid, if low, add more distilled water. maybe it has too much coolant and cant heat up. but then again. do you park your car outside? if you do, dont add water to your radiator. seeing as how you said its 20 - 30 degrees outside, if you have too much water in your radiator you could crack it.

celicaGT90_05
03-06-2008, 05:20 AM
seems like theres a misconception of coolant here, so I'll clear it up. Coolant is the blend of antifreeze and water, thats practically all there is besides some additives to help lubricate the pump and maintain seals. Too much antifreeze wont cause a car to overcool, but can harden and build up on the pipes and water jackets and clog paths in the radiator and heater core but wont do it right away, usually takes a while but make sure it is a blend of water and antifreeze. This can however cause your car to overheat and poor heater performance. You can run strait water and it wont cause it to overcool either, but you wont get proper lubrication to the water pump and if it freezes you stand the chance of busting hoses or other things. You also cant fill the radiator up too high, you are suppose to fill it up completely to the top of the cap, work out any bubbles, and top it off all the way, then fill the overflow up as much as you can because you will draw in more coolant rather than air as parts expand. Also too little coolant will cause overheating and poor heater performance

As for the temp switch, I'm not sure where exactly it is, but it should be right by if not in the block because it is trying to detect engine temp as accurately as possible. I do recommend checking your thermostat though, if its not the problem it will be closed.

supra97rx7
03-06-2008, 05:33 AM
radiator fluid is good already.
i do park it outside, sometimes, but this isssue (well, the idle issue) has been going on ever since we've had it. it's just now that i really paid attention and noticed the temperature changing

celicaGT90_05
03-06-2008, 05:39 AM
change the stat, they are a common issue, and they are no more than $20 and are a pretty simple fix. If you need any assitance as to how I'll be more than happy to help

supra97rx7
03-06-2008, 05:47 AM
alright. i guess i'm pretty set on doing that. i looked up thermostat removal in the BGB.

will it be obvious what the "engine coolant temperature switch connector" is, since it should be disconnected?

when you buy a thermostat, does it come with a gasket or do you have to buy it separately?

celicaGT90_05
03-06-2008, 05:50 AM
ask them when you go to get it if it comes with the stat, my dads did when we replaced it on his ranger, but it may be different. And its unlikely the sensor will be unplugged, whats mor likely is build up of corrosion causing excess resistance. However, see what it does when you replace the stat, and if the problem doesnt persist, then theres no need to worry about the switch

supra97rx7
03-06-2008, 05:57 AM
okay, i shall do that.

one last thing - with thermostats, does it matter if you get a cheapo stat for like $7? i was looking at o'reillys website to see what i could pick up tomorrow.
but there's also beck/arnley $22, failsafe, valucraft, and duralast at autozone.
and BGB says it opens at 80 celsius - for the new stat, does it need to be the exact same?

celicaGT90_05
03-06-2008, 06:13 AM
thats up to you, the price is usually due to the quality, so it may only last a year or 2 while as the others may last longer. Higher end tends to have lifetime warranties. If you want to go cheap, its your choice. As for valucraft, I'd steer clear and Im not a big fan of duralast either, I've had better luck with advance parts

supra97rx7
03-06-2008, 06:19 AM
alright. so opening temperature just needs to be pretty close? doesn't need to be exactly right?

celicaGT90_05
03-06-2008, 06:27 AM
get it as close to factory as possible, a little higher wont hurt

hobbie2k
03-06-2008, 06:18 PM
It's almost definitely the thermostat, easy fix.

My wife's Hyundai had exactly the same symptoms...Even in 90 degree weather, at highway speeds the temp needle would be buried on cold, but after a few minutes of idling it would be back at normal.

ciento44
03-06-2008, 06:55 PM
It's almost definitely the thermostat, easy fix.

My wife's Hyundai had exactly the same symptoms...Even in 90 degree weather, at highway speeds the temp needle would be buried on cold, but after a few minutes of idling it would be back at normal.


Mine does that, but i don't really see it as a problem.

The fan WILL kick on at idle before it hits even halfway up the guage.

celicaGT90_05
03-06-2008, 07:26 PM
overcooling is an issue, if its an automatic it can prevent the torque convertor clutch from engaging, and also your engine will run richer if too cool because it is attempting to warm up

supra97rx7
03-07-2008, 01:06 AM
okay, so i replaced the thermostat with a new one
warmed it up
drove it around
engine stayed warm, and the heater was blowing hot air like i've never felt before.
case closed.
thanks a lot everyone

celica9303
03-07-2008, 10:05 PM
My gf lhs that we just got 3 days ago overheated lastnight and the coPolant tank was empty so I filled it and burperd it, it started to overheat again so I changed the t-stat to a failsafe and did it again(didnt over heat when i drove it for about 30 mins, after it ran with the rad cap off for 30 mins), she drove it to work today and it ran cold while moving and warm while idleing could there still be air in the system? I'm gonna look at it again tonight any help is great, this problem just started lastnight. Sorry for the spelling I'm on a blackberry

cant find any leaks either hoses are tight and all that. ive never owned a domestic before so dont know much about them,
pass florboard isnt wet either (will check that again when she gets home from her drive(hour away form work))

DarkSideCelica
03-07-2008, 10:35 PM
t-stat fo sho.. i replaced mine a few months back.... didn't see the effect of s stuck t-stat till winter came around

celica9303
03-07-2008, 10:56 PM
any ideas on the LHS?

G.W
03-09-2008, 07:31 AM
Sounds like a water pump, fans not kicking on, or low coolant.

celica9303
03-09-2008, 09:56 PM
Not sure replaced fan fuse and drove it did the same thing.... Coolant is full gonna swap out the t-stat again tonight