Mystery overheating may be due to cooling fan

Dear Car Talk:

After weeks of visits to two different mechanics, over $1,000 paid in repairs and three tows in two weeks, I am finally getting desperate enough to write to you guys!

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 to finally be healed – for a week. Then, my son drove the car for 2 1/2 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 then 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 airflow stops, and you need an electric fan to blow air through the radiator.

So, check and see if the cooling fan is cycling on and off like 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.

Manual shifting provides more power

Dear Car Talk:

I have a 2016 Hyundai Sonata. It has a “Sport Mode” that is supposed to give you more power. Sometimes, I’ll use the automatic shifter to shift up through the gears myself and get to higher rpm.

It seems like when I shift the gears myself, I get more power than I do in Sport Mode. Is it my imagination or does shifting myself give me more power? – Maureen

RAY: It's not your imagination, Maureen. You're probably getting a little more power by keeping the car in each gear longer. You're certainly getting more noise, and that also contributes to the feeling that you're going faster.

In most standard passenger cars (of which we’ll categorize the Hyundai Sonata), there’s a button called “Sport Mode” or something like that. Since transmissions are electronically controlled now, that button simply moves the shift points higher. So, under normal circumstances, if the transmission would shift gears at 2200 RPM, in Sport Mode, it might shift at, say, 2800 RPM.

The higher the engine rpm (up to a point), the more power you get. Also, the lower mileage you get! Which is one reason the car doesn’t run in Sport Mode by default. The other reason is the noise. Most people prefer quiet and higher gas mileage to a little zippier acceleration. But if Sport Mode causes the car to shift gears at 2800 RPM, you can certainly wait longer than that when you do the shifting.

So, if you’re shifting at 3500 or 4000 RPM, the car is going to feel (and definitely sound) like it’s going faster than it does in Sport Mode. If that still doesn’t feel fast enough for you, Maureen, try chiseling a hole in your muffler. That’ll make it sound like you’re flying.

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