Just a coolant leak or something else?
 

I have a 1996 Camry LE with 270K miles. Yesterday I noticed the heat gauge going up into the hot range while idling in the parking lot after a 45 min drive to work. My fans were on while it was getting hot. I turned the engine off immediately, no steam or noticeable adverse damage was done. Went into the building and let the car cool down for a few hours. Came back out to the car about 5 hours later and checked the radiator – it was full, cap was secure. Radiator is new within the last two years. Checked the coolant reservoir, it was completely dry. I added 50/50 coolant to the fill line. Drove 45 mins home in stop-and-go traffic and the gauge stayed within the normal range the whole way home. Car sat overnight for about 13 hours…I checked everything again before my 45 min morning commute. Radiator still full, cap secure and tight, but coolant reservoir was empty again (less than 24 hours later). Refilled the reservoir and got to work OK, but it seems that there is a big leak somewhere because I have to constantly refill the reservoir after each drive I take.

When I fill the reservoir, there are no noticeable leaks from the container itself. The one hose that I can see running to the radiator from the reservoir appears to be in good condition with tight seals. There are no noticeable leaks on the ground from any coolant leaking when car is hot or idling. Nothing is leaking within the interior of my car. (Maybe there are leaks I am not seeing?) I do not smell coolant in any way when car is running. Any ideas what is going on? I am assuming this is a coolant leak, but don’t know what else I should be looking for.

I need to know if this can be a DIY project, or if it is indicative of a larger problem and should go to the mechanic. If this is a decent DIY thing - any suggestions on where to get the parts or tips on doing the work would be great.

Is this the first time the engine overheated?

Could have been a stuck thermostat, if everything is otherwise OK would start here.

Don't let the engine temp go into the red even if you need to stop and wait until it cools.

Place cardboard under all of the engine area when hot and check for coolant.

Check the following areas for signs of coolant:

Plastic shield under the bottom of the radiator.

When engine cold feel all coolant hoses for leakage including the ones that are hidden such as the bypass hose coming off the coolant exit manifold on the head.

Under the timing belt cover.

Heater valve on heater hose next to firewall.

The carpet under the dash.

Make sure the radiator is full, fill the overflow plastic reservoir tank and note the level. Right after the engine is shut down hot for overnight check the level of coolant in the overflow tank reservoir. Is it higher or lower, empty?

There are dyes that can be put into the coolant the show up under black light.

Start by determining if there is an external leak. If there is no leak the coolant is going somewhere else, this may mean out the exhaust via a blown head gasket.

My '94 V-6 had the same symptoms. Water gradually disappeared from reservoir tank and some from the radiator. I worried it was a bad head gasket.

Loss was very sensitive to outside air temperature. In cooler months I only added water once a week. Turned out to be a bad water pump. It got progressively worse.

If your situation is caused by a failing thermostat, try adding a can of water pump lubricant to the radiator (not the overflow tank). Sometimes that will unstick things. For $4.99, or so.