Temperature gage climb to 3/4 at hot weather

[Marik123]

I own a 2000 Mazda Protege LX 1.6L auto. Ok, recently I notice the temperature gage climb to 3/4 at really hot summer days. If I don't turn on the A/C, the temperature gage will stay slightly below 1/2, but once I turn on the A/C for 10-15 minutes, then the temperature gage will slowly rise to 3/4, and then couple minutes later slowly drop back down to slightly below 1/2. Yesterday it was close to 100C in my area and I notice the gage climb to 3/4, so I immediately turn off the A/C to let the engine cool down. But it will still climb higher than 1/2 like say to 3/5 but it drop down after 2-3 minutes and then raise back up to 3/5 2-3 minutes later. It raises and drops slowly and happens every 2-3 minutes cycle. So what's going on here?

This only happens when its really hot outside and doesn't happen when its colder weather like say less than 90F. I mostly do highway driving and maintain 60-65MPH.

1. When the engine is cold, I open the radiator cap and the coolant is green topped, so I can assume the radiator cap is good and coolant also good.
2. When I turn on the A/C, both fans are on. However, the fan close to the water pump blows really hot air and the other fan blows hot air, but not as hot as the one close to the water pump.
3. The drive belt has been changed 2 months ago and that includes the water pump ac and alternator belt from Meineke. I even had them check for my cooling system for any defects and they told me everything is fine. They plug a computer into the car and check for any problems. They told me your fans are working when A/C is on, your coolant is at full and looks good, and your thermostat is opening when its hot and there is good flow in the cooling system. Probably its just a really hot day and you experience that and your cooling system is fine.
4. It could be the coolant temperature sensor is faulty, but at colder days it stays below and goes to when its really hot outside and then drops down to after 2-3 minutes. That seems normal to me

Im out of ideas here (uhm)

 

[mig360mBJ]

change thermostat flush coolant

 

[Kaido]

change thermostat flush coolant

How abt change Koyo Radiator?

 

[dredman]

When you checked your fans, was the engine overheating then?
Had a similar problem a couple months back, so when I reached home I checked both fans and they were both working.
Next day, however, in traffic the car started overheating again, so I switched off the a/c. Temp still went up. Pulled over and checked it then, and saw that the engine fan wasn't on (although it worked the night before when I checked at home). Tapped the motor housing with a spanner and it started spinning slowly. Ended up needing new engine fan motor. A/c fan was on when I used the a/c, but it alone wasn't enough to cool the engine. When I switched off the a/c, the a/c fan switched off. And since the engine fan wasn't working - overheat!!!
Check your fans when next the engine is actually overheating and see if they are both working.

 

[Marik123]

I took my car to Meineke last Saturday and they said they couldnt find the problem. They are telling me when you turn on the A/C, both cooling fan is working fine and the car is not overheating. They attached a computer to my car and they said when the temperature raise, the temperature sensor voltage drops, so the sensor works fine. They are showing my coolant temperature is at 223-225F steady with A/C on. They even used a laser gun to check for the outside temperature and it shows the same. 223-225F right on the coolant temperature sensor outside and the radiator/hose shows 180F-185F. Water pump is working radiator is not restricted and the coolant is excellent. They are telling me it's probably a partial stuck thermostat like it's not opening wide enough at extreme hot weather, so I'm going to take it back to them today when I actually drive back from work, then the car will show the symptom I described. However, yesterday is just 70F and the coolant temperature is 223-225F with A/C on, what if the weather is 100F? Wouldnt that make the coolant close to 255F, thus overheat?

 

[Marik123]

Here is one more thing I notice. When I use the laser temperature gun and point to the coolant temperature sensor near the top radiator hose, it shows constant of 223-224F. But when I point to the upper radiator hose itself, 180-185F, so does this mean I have a partially stuck thermostat, or you guys think its a clogged radiator? I took my car back to Meineke and they charge me $120 to replace the thermostat and I found out it's just on the top radiator hose which can be change by me easily for $15. They also suggest I should take the car to the radiator specialty shop and have them take it out and check the flow. But if the radiator is really clogged, it doesn't make sense to have the coolant temperature sensor at 223-224F and the radiator hose next to it with thermostat below to be 180-185F. So if I want to change the thermostat myself, do you guys think its a difficult task to do?

 

[ghostbusters]

sounds like thermostat issues

 

[Marik123]

I took it to the shop and had them replace the thermostat, fully flush the coolant, replace upper radiator hose and replace the radiator cap. Now the car runs fine now and no more overheating. My car used to ping at hot weather and now it doesn't ping even with AC on.