1997 Camry Temp Guage Fluctuates

My girlfriend's 1997 Camry with about 150k miles has a temp gauge that fluctuates between just above cold to about half. I noticed it gets hotter when idling and gets down to near cold when light on the gas and at a good speed (such as downhill coasting).

I am not at all familiar with Toyotas. Most I did on her car was change the oil a few times. I suspect it's the thermostat, but before I go pick that up, are there any known problems with the cooling systems on these things?

With that said, if the t-stat needs replacement, where can I found instructions on how to flush the cooling system and what anti-freeze product do you recommend? Again, I've never worked on or owned a Toyota so any help is appreciated.

Your girlfriend's car has all the symptoms of a thermostat that is stuck in the open position. I would be willing to bet the heat also fluctuates somewhat as the temperature gage goes up and down. The needle should rise to just a bit under halfway on the gage and stay there. I would recommend a Toyota OEM thermostat and gasket. They are generally just a few dollars more than aftermarket and have a jiggle valve (a little bypass hole) that goes at or near the 12:00 position. As far as instructions you can download an entire generation 4 Toyota factory service manual at the top of this forum's home page. Refer to the cooling system section for her particular engine on how to change the thermostat. As far as the type of antifreeze, that's really up to you or you could just get the recommended Toyota antifreeze at a dealer. Again it will be a bit more than the aftermarket stuff.

Mike

And after you change the thermostat make sure you use a distilled water when diluting the coolant. I'd say use the premixed 50/50 mixture, but I don't trust the manufacturer to actually use the distilled water in their mixture, parts store says they do but do they?

A bit more of a pain, but buying full strength and diluting with distilled water saves money versus pre-mixed 50/50. $11 ($10 for full strength + $1 for 1 gallon distilled water) to make 2 gallons coolant while it is $8 to get one gallon of pre-mix. But the premix is handy when you need to top off.

I always run up to Walmageddon or whatever place is nearby and get a few gallons of distilled water to flush and fill cooling systems. I find it pretty easy to make a 50/50 mix as long as I know what the capacity of the system is.

I was hoping this would be easy like mine - remove 2 bolts, replace o-ring and t-stat, tighten bolts, and top off degas tank. But it does not appear that way after looking at the service manuals. Let the games begin!