Overheating/Coolant mystery

[josephmartins]

This thread was previously titled "OBD II Codes....can they be obtained without a scanner?"

I just had an opportunity to dig into the car and see what's going on. Codes aren't an issue now as the system apparently reset itself and all engine lights are now off. I'll begin with what I wrote earlier and add the updated information.

Earlier I wrote...

It's a 2000 Toyota Avalon XLS V6 with just over 90k miles on it. Yesterday, after just 3-4 miles of driving on an already warm engine (driven earlier that afternoon), the engine light lit up. Shortly after that the VSC lights lit up. I've heard that the check engine can trigger the VSC lights so I thought nothing of it. A couple miles later the temp gauge pegged and I could both smell an odor and hear an unusual, barely audible "scratchy" sound. I assumed a problem with oil/coolant.

Initial visual inspection showed no fluid leaks...just condensation off the AC. I let the car sit and cool down and still no sign of leaks. Had it towed home and I plan to dig into it today to see what is going on.

Vehicle's owner who was in the car at the time says a mechanic told her, during her last vehicle repair, to keep an eye on her radiator as it "might be going". I saw no indication that there was a radiator issue. Thermostat malfunction perhaps?

As of a few minutes ago, here's what I discovered....

So, I began filling the radiator with straight H20 just to see how much it'd take. It took more than 1.5 gallons. Apparently, since yesterday quite a lot of coolant disappeared. Either that or the coolant level was already extremely low but I find it difficult to believe the owner could have driven 30+ miles earlier during the day yesterday on almost no coolant without overheating. Then again, maybe she did. She certainly didn't check the coolant level beforehand so I cannot say one way or another.

I started the vehicle and idled it while adding an additional 1/2 gallon or so to top it off. I continue to idle the vehicle until it came up to temp. Turned on the AC to stress the system and the fans turned on as expected. Ran it with AC for a few minutes which only moved the needle northward maybe 1/8" inch. Shut the AC off and the temp settled in about 1/4" south of the midpoint marker on the temp gauge. Looked beneath the vehicle, and still no visible leaks. Checked the dipstick and the oil seemed fine.

I then took it out for a spin for just a few miles. Temp didn't budge and everything seemed normal. Pulled into the driveway and checked again for leaks - nothing. Shut if off and let it sit, still nothing.

So it seems the overheating incident yesterday was due to the coolant system, but I'm baffled by what it could be. I expected to see at least some leaking or perhaps water in the oil, but I found nothing. While I haven't driven it hundreds of miles to stress test it, it's not currently running hot.

Any ideas? Could that much coolant have evaporated from the system yesterday afternoon and then through the evening as the engine cooled? If it didn't evaporate where could it have gone? I had not touched the radiator cap until today, but even assuming a bad cap I find it very difficult to believe a couple gallons would disappear. I'm stumped.

[TrailDust]

One way or another you're going to have to hook your car up to a scanner to read the code/codes.

[chuckoff]

A very slisht leak could cause loss of coolant and overheating. You need to have the cooling system pressure tested to check for leaks. A tiny leak may not be visible while the car sits and be small enougt to evaporate if leaking while engine is running. Mechanic saying keep an eye on radiator probably meant the plastic tanks are looking old. These can crack with age or, leak at the seam between the radiator core and the tank.

[josephmartins]

Thank you both. I suspect you're right chuckoff. I've been driving it locally with straight H2O the past day or so and it must be a very small leak of the type you described. I see no drips but it's definitely evaporating.

I'm about to order a replacement radiator for it - I'm willing to bet there's a crack in the plastic as you suggested. I see there's an OEM replacement and there's an all aluminum replacement for just $25 more.

[TrailDust]

Before you purchase the radiator, have you had the system pressure tested yet?

[BiXLL]

I at one time had a 3.1 GM V-6. These motors were famous for leaking coolant at the intake, and buring it up. There was never any signs of leaks or smells, just disappearing coolant. It had no effect on how the car ran either. The proper way to fix this was to replace intake gasket, but I got about 35,000 miles out of it just using a double batch of stop leak. Traded the car in with 160,000.

[josephmartins]

I haven't, TrailDust...not yet. Is there a feasible way to pressure test it myself? Otherwise she's looking at having to have the car towed to the nearest shop quite a few miles away. I figured for not much more than the cost of a tow and pressure test I could pick up a $115 replacement radiator (and hope like heck I nailed the cause)...lol.

BiXLL, I thought about a possible manifold leak but I'm hoping that's not the case. If it is this is going to be a loooong week.

[BiXLL]

I believe Autozone or Advance Auto has a coolant system pressure tester you can use.