just recently ive noticed when i use my a/c my temperature gauge has the tendency to start rising. I never let it raise to the last quarter of the gauge because i shut my a/c off once i notice that the needle isnt in the normal operating area. i replaced my coolant thermostat about two years ago. im not sure if that would be the culprit again? or just something else thats going bad. all my fluids are fine and my fans work. any idears?

 

if your temp gauge is going over half way, that is not good!
you can blow a head gasket that way!

the first thing I would do is replace the gauge sensor itself, the real Toyota part is only about $15 online, then you know the real temperature of things.

the main reason turning on the A/C would make the temperature go up on a weak cooling system is not, as myth would have it, the extra strain of turning the compressor (this is child's play for a V8)

the real reason is that red hot freon in your condenser in front of the radiator


why is the freon getting too hot?

normally one of the following:

● fans really are not working some of the time (usually that sensor in the radiator)
● A/C system overcharged with refrigerant
● blockage in condenser/radiator grill (clean out the dirt, bugs, plastic bags, etc.)
● fan clutch


these below don't make the freon hotter but could put the cooling system on the edge of its ability to cool the engine

● thermostat and or temperature control on the thermostat (the beeswax thing on older models)
● low or incorrect coolant
● bad radiator cap
● broken water pump impeller
● clogged radiator (high mileage cars that didn't always run Toyota red coolant)

 

the factory coolant temp gauge is "stupid". Anything within 1 bar in each direction from center is considered "normal". If it goes above that, then you should pull over/worry.

Given the high temps here in socal recently (105-110+ in some areas!) this isn't entirely surprising. Just make sure you don't have an air bubble in your coolant by burping the system again and keep an eye on it, esp when the motor's loaded up for a long time (ie-AC on in traffic or AC on long prolonged climb like the baker grade).

 

i only do about 45 miles of driving a day when i goto school. i thought it was pretty odd since i noticed it when i was doing more driving than usual and running some family members on errands. and i only really use the a/c when theres other ppl in my car, or just to get rid of the heat inside when my car sits. ill be sure to check for any type of blockage and also burp my coolant system while im at it. i just want to be sure if this is the proper way to burp it.

1. Remove cap
2. turn on car
3. put heat on highest setting
4. rev engine around 2000rpm for several minutes
5. turn off car and let cool down
6. add toyota coolant to full level
7. replace cap

i also wanted to note that my temp gauge needle is always in this area and i never let it go past the next line when i noticed it rising.

 

you have to run the car until it hits operating temperature.

I prefer to bleed from the fill point on the throttle body. It's been detailed on the forum a few times.

 

i too was going to suggest you have air in your cooling system. i had this problem after replacing the water pump and failed to extract all the air out of there. once a proper bleed was performed, no more rising in the needle especially in our current heatwave here!

 

My temp needle is exactly in the same position as yours - just a hair above that line, just like in that picture.
Out of curiousity, I once decided to measure the exact temperature of the coolant after I drove my '90 LS400 in hot weather for hours. I just stopped the engine, opened the plug near the thermostat within seconds of stopping the engine, and used digital thermometer which is really accurate within 0.1 F.

The result? Coolan temperature was 188 F.

I am mentioning it here also as a reference for everyone else - assuming that you have a first gen and your needle is in the same spot and all your sensors are working properly and coolant is good and there is no dirt in the cooling system, that is very likely your temperature also.

 

When i chased my temp gremlins turned out to be a faulty temp gauge. After 20 years it goes out of whack.

 

be sure to use the genuine Toyota thermostat built by Kuzeh, and make sure it is clocked properly (the jiggler hole should be at 12 'o'clock to allow the air you are trying to burp out to pass through!)

if you have the thermostat clocked correctly, and the genuine Toyota one, and the system is full at the FILL BOLT (the downward aimed large bolt right behind the thermostat) and a nice new genuine Toyota radiator cap, the system will self-bleed over repeated warm up and cool down cycles as you drive the car over a few days, no special bleeding procedure is necessary, you will notice the level in the overflow tank fall as this is happening. So be sure and keep it topped up to the MAX line!

my properly running 96 LS400, with new gauge temperature sending unit and OEM thermostat stays a little below halfway on the gauge, year round! (where it should be) and your photo depicts the correct place, now address that excessive freon temperature and you will be all fixed!

if everything is working correctly, there will be no difference in temp gauge reading with A/C on or off!