Hello all, I just purchased a 1999 Toyota Camry LE with 162,000 miles on the 2.2L. I noticed when test driving it and driving it home that the temp gauge goes down to the cold mark (scan tool says 150F) when driving and when stopped at a red light it will climb up to normal operating temp (170F-ish) When I googled the problem I saw two other people have had the issue but never found a fix. Any help will be greatly appreciated.

 

The car has the symptoms of a stuck thermostat. Suggest doing some investigation prior to taking the coolant system apart to check the thermostat.

Once the engine is warmed up the temp gauge should be rock steady. The temp needle typically just below the mid mark on the gauge. What this needle position corresponds to in terms of actually temp don't know. The coolant system should have a 180F thermostat and thus coolant temps run 180F+

The coolant system uses a combination of radiator fans and the thermostat to keep the coolant temp constant.

In stop and go traffic or at prolonged idle the fans will turn on/off to aid with airflow through the radiator. They turn on at around 199F. If the A/C is turned on, the fans will also cycle on/off in sync with the A/C compressor turning on/off.

Start by checking the coolant level in radiator. Too low of coolant can cause temp issues.

Determine if the radiator fans are not stuck in the on mode, as in they are on all the time.

When coolant is cold, remove radiator cap and start engine. Watch the coolant flow. With thermostat closed there would be minimal circulation. The circulation increase as the coolant temp increases. Its OK to operate the engine with the radiator cap off at idle. The radiator fans should start up around 199F and on a properly operating system will start turning on/off. Who knows if your car will reach this temp. As stated a normal coolant system will have the gauge reach midpoint and stay there. Keep you head away form the radiator fill point in case the coolant spurts out when hot.

Air in the coolant system can cause issues but these tend to cause higher coolant temps.

From here check out the thermostat to determine if its its stuck open, not the correct one (too low of temp settings) or missing (this has happened on used cars to hide engine problems such as a blown head gasket).

 

Heat works great. I checked the t-stat housing and upper radiator hose with an IR gun and got 160F on the t-stat and 150F on the hose so what the scan tool is showing appears to be correct. When I googled and saw that other people had the issue they had replaced the thermostat three times and tested each one. They also replaced the sensors to no avail. I checked the coolant level and the radiator was full to the top, I topped off the reservoir. The timing belt was replaced about 10k miles/2 years ago and I can see that the water pump is circulating. I let it run for about 20 minutes and the gauge was almost to operating temp. I had the heat on the whole time and never saw any bubbles coming out. Tomorrow I'll check cooling fans and let it run longer and see how warm it gets. No signs of a blown head gasket and t-stat housing doesn't look like it's been touched in a while. Thanks for the help.

 

With 90% of the radiator covered with cardboard, it will warm up to 170 when idling but still drops down to 145 when driving.

 

I'm gonna order a new gates t-stat and gaskets from RockAuto and test the old one and new one before installing. I'll report back.

 

Should be a 180 degree thermostat.

Valve should be fully closed below 140F.

Should start to open between 176 and 183F.

Should be open .31+ inch at 203F.

Make the jiggle pin is in line with the protrusion (located up) on the T-stat inlet holder.

 

I don't know exactly, but I think the whole reason is in the clogged radiator. You need to clean it and look for defects. I had a similar reason. I made my choice here silverado radiator upgrade. How to replace the radiator, you can see in the manual for your car. You also need to periodically check that there is a sufficient amount of liquid in the radiator.

 

Whoops, I forgot I made this post!
The Gates t-stat I installed was bad out of the box and the problem didn't change which led me to believe the t-stat wasn't the problem. I should mention I did test the Gates t-stat and it was within spec but for whatever reason still overcooled. Then a couple of months ago I installed an Aisin t-stat that immediately fixed the problem and now the engine warms up as it should.

 

Thanks for posting back with the fix!