Overheating mystery

Honda civic ex 2001 w/ 202k miles… I am not a car guru, so will do my best. 1 mo. ago was driving on highway, the a/c started going, then I began losing power, temp went hot, pulled over steaming hood, wouldnt take much water. Mechanic did: replace thermostat,therm gasket,new radiator fan temp switch,pressure test.
Ran fine for 2 weeks, then heat began to rise again & overheated. Each time it overheated the top small hose on radiator popped off(like a 1/2 in. hose).
Back to mechanic: did pressure test, did a full cooling system test all were great…Only thing he found was a small radiator crack…thought it just took a week to lose coolant. Replaced radiator/ecu temp sending unit/refill and pressure test.
1 week later, temp spikes to hot, so I bring it back…he tested pressure/flow no leaks again…he can’t figure it out.
One note: for about the past 3months, right after starting, I would come to my first or second stop, then accelerate and hear a squeal that lasts like 5 seconds or so…this happened intermittently for about 3 months, and is still happening(I can drive very short distances now).
A friend thought the issue was the belt that controlled the a/c and 2 other things.
Any ideas would be greatly appreciated.

When was the water pump and timing belt change last? It could just be poor cooling under load. At this age it could be crud in the radiator as well. A/C puts a heat load on the radiator. If it is plugged or the water pump is not up to the task you can get too much heat. That said you have issues that a a bit puzzling. You said the small radiator hose popped off? The little one that goes to the reservoir? I’m not sure whether you said you were leaking coolant normally.

Here’s what to do first: When it overheats, pull over, keep the engine running, check the dashboard guage. Does it indicate hot? Then pop the hood and check if the radiator fan is spinning like a banshee. It should be. If the dash guage says “cool”, and/or if the fan is not spinning, there’s still something wrong. Then turn the engine off of course until your mechanic figures out what is wrong. Anytime the engine overheatds, it can damage the head gasket, or worse.

Probably the next thing to do is ask the mechanic to check the oil and coolant for cross contamination. A cylinder leakdown test would verify the head gasket is ok (or not).

In any case, be safe about how you approach this. There’s no point opening the radiator cap when the coolant is hot. Let everything cool off before messing w/stuff under the hood.

Overheating can be caused by quite a few things. And it is sometimes difficult to decide what is the cause, and what is the effect. A leaking radiator can be a cause, or it can be an effect of something else being wrong.

Just a guess, possiblities in decreasing likely-hood are:

  • Faulty A/C compressor is seizing
  • Stuck thermostat
  • Faulty coolant temp sensor
  • Faulty cool temp switch (for fan)
  • Faulty radiator cap
  • Faulty water pump belt
  • Faulty water pump
  • Faulty auto-xmission (if auto)
  • Faulty head gasket (knock on wood it is not this)

Op already said many on your list were done and some twice. Your list is a bit shooting in the dark, but we do that sometimes.

It sounds like the head will be coming off soon. It is likely warped or cracked or the head gasket is failing.

Assuming you have an automatic transmission, I’d look there. I don’t know for sure, but the transmission fluid probably runs through the same radiator as your coolant. You’ve had your cooling system thoroughly checked, repaired and rechecked. It’s time to look at something different but related.