DEAR CAR TALK: After weeks of visits to two different mechanics, more than $1,000 paid in repairs and three tows in two weeks, I am finally desperate enough to write to you.

I want to extend the life of my 2002 Buick Rendezvous. I inherited it after the engine had been replaced (in 2007).

We found we needed to add additional coolant about every six months, until a couple of months ago when the temperature gauge suddenly went red.

We added coolant and our mechanic replaced the thermostat and flushed the system. Days later, it happened again, and the car died on me, but miraculously worked fine once it got back to the shop. I was told it had a “bubble in the coolant line.”

Two weeks later, it overheated again, and a new mechanic replaced some parts for $700 – he said the tubes might be clogged in between the radiator and engine.

On the way home, it overheated and died. So, back to mechanic No. 1 for a new radiator and another new thermostat.

All seemed finally healed – for a week. Then, my son drove the car for 2½ hours on the highway, and when he came to a stop at a red light, the temperature gauge went red again, then went back to normal by itself once he started driving again.

It happened twice more on his way home. The car has been sitting unused for a week while we try to figure out what to do next.

Any suggestions on how to repair the coolant problem? Kind regards. – Mrs. Martinez

RAY: Are you sitting down, Mrs. Martinez? If you’re incredibly lucky, and you’ve lived a good, clean life, you may just have a bad cooling fan.

When the engine is at operating temperature, and you’re on the highway, you get plenty of airflow to cool the engine because you’re moving. That air that blows in through the front grill keeps the engine from overheating.

But once you’re stopped at a red light, the natural air flow stops, and you need an electric fan to blow air through the radiator.

So, check to see if the cooling fan is cycling on and off as it’s supposed to. If it’s not, maybe the radiator solved the problem, and all you need is to fix the cooling fan. If the coolant fan is coming on and off, then the news is far more serious.

Mostly likely, you needed a radiator from the very beginning. But, unfortunately, during one of those four (or 14) times you overheated the heck out of the engine, you blew a head gasket or cracked the head. Or worse, cracked the block.

So, start by figuring out if the cooling fan is working properly. If it is, ask your mechanic to test for a blown head gasket or cracked head or block. We use a dye test, or we test the radiator vapors for the presence of exhaust.

If the tests come back positive, and the rest of the car is still in good shape, then it’s time for engine No. 3, Mrs. Martinez.

And this time, ask them for one of those punch cards, so when you get to your 10th engine, you’ll get the 11th for free.

Got a question about cars? Email Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.