Overheats on hot days but dealer could not find anything wrong

[Planetoid]

My 98 Escort started overheating a month ago, but only on hot days over 90 degrees, and mainly when sitting still in traffic. Using the AC makes it worse. Turning on the heater helps cool the engine, but it's not a fun way to drive . I left the car at a Ford dealer to diagnose the problem, but they said everything checks out fine (fan and thermostat work, etc.) They flushed the coolant, but there's no change.

As the car warms up, the temp gauge stop climbing when it hits the 12:00 position, but it starts to climb again on hot days when I stop. The car has 135,000 miles, and this was only the second time I had the coolant flushed, so maybe the radiator is a little blocked (even though the dealer couldn't diagnose it?) . What would be some cheap ways to try to fix the problem, e.g. replace the thermostat?

[mightymoose_22]

How high does the temp climb?

What you are describing sounds normal. The temp will reach a point and stay there... and at idle or low speeds it may continue to climb. When the temp gets high enough the high speed fan should kick in and knock the temp back down a bit. It is normal for the temp to cycle that way. If the fan is not turning on and causing the temp to drop back down (temporarilY) or if you are redlining, then you have a problem.
If you are sure there is a problem, you would be correct to suspect a blocked radiator or possibly a faulty pump. If you haven't had the coolant changed regularly then you may just have build up. A flush of the system won't necessarily free it up.

A check... when the engine is up to temp (thermostat open) feel for pressure on the upper radiator hose. In fact, you should be able to keep a hand on it before the thermostat opens, and feel a surge as the hot coolant comes through the hose when the thermostat opens up. There should be good pressure there. If no pressure, or weak, thermostat is not opening properly (though I think yours is fine since you do not run hot all the time), water pump is faulty, or blocked radiator. I would begin with the radiator.

[KimMG]

Did the service tech check the radiator for blockages internally and externally? Bugs and other road debri can block air flow through the fins of the radiator. A partially internally blocked radiator will reduce coolant capacity in the radiator. How old is the water pump? Old water pumps may have worn vanes reducing their circulating ability.

[markwb]

You could do another flush with a good backflush & new t-stat. If that doesn't help then I'd look into a new replacement rad. One way to check flow through the rad is this. With cold engine, remove the rad cap, turn heater to max., start engine then allow engine to warm up to operating temperature. you should see coolant flow (looking down though filler neck of rad) as t-stat opens up.

[Paul78zephyr]

Originally Posted by Planetoid

My 98 Escort started overheating a month ago, but only on hot days over 90 degrees, and mainly when sitting still in traffic.

That is a major clue that your problem is probably due to a problem with your electric cooling fan. When the car is in motion it gets airflow thru the radiator from the forward motion. But when you are standing still the electric fan is ESSENTIAL to getting airflow thru the radiator. The fan has two speeds, low and high. You must make sure the fan will run on BOTH speeds.

Paul

[Planetoid]

Mightymoose, the temp gauge goes halfway up to the red . It's not normal because it never went beyond vertical (12:00) until now, after 8 years. I'll try your rad hose check and Mark's visual check.

KimMG, the water pump is the original one (98). I'll find out if the deal did both internal/external rad checks.

My first guess was the fan wasn't working, since it's mainly a problem when I'm stopped, but the dealer said it's ok. Maybe only the low speed works, as Paul78zephyr suggests. I can't see the fan because it's enclosed, but I'll listen for different levels.

Thanks
Planetoid

[mightymoose_22]

A quick check of the fan... when the engine is cold (I think it only works when cold) when you turn on the engine the fan should aperate for a few seconds and turn off. Also, turn on your AC and then fan should operate as long as it is turned on.
If your fan does not operate either of these times... something is wrong with it. Obviously, if it passes both tests... no fan problem.
I think if something was wrong with the fan the dealer would have identified it.

It sounds as if your problem may be poor circulation... you just need to figure out the cause.

I understand that you have not noticed this problem in the past... but still, what you describe does not sound like a problem. A gauge that is only half way to red does not sound so bad. Has your thermostat ever been replaced? Do you know what it's temp rating is? Maybe it is taking longer to open than it used to... but still... not so much of an "overheating" problem as it is just running hotter than it has in the past.