Cant figure out this cooling issue

[Tragertt]

So I have been dealing with this for some time now and its getting old, my 96 montero wont stay cool when its hot outside. Let me start with what I have done and what the symptoms are. I have replaced

1. Thermostat
2. Fan clutch
3. A/C fan
4. Coolant flush

When it is 85 degrees or below I have no problem, I can run the AC or do anything and it stays nice and cool. With it is hotter outside I can run the AC and it will stay cool for awhile but then after 20 minutes or normal driving the temp starts to go up and when I stop it goes up fast. It has never overheated or spilled coolant so my first thought was maybe a bad temp sensor on the thermostat housing but that doesn't seem to fit to me, it works when it is cold outside so i'm not sure. When the car does start to get warm and I turn the AC off the temp gauge instantly drops 20% or so and then slowly cools down from there. A friend of mine thought because of the instant drop in temp when i shut off the AC that maybe I have a bad ground wire from the engine to the frame or for the accessories a bad ground to the body. There are only a few more parts I can replace like the radiator and water pump but i'm not sure if that is necessary. Any suggestions on this would be amazing, thanks guys!

[off-roader]

How many miles on the rig? As a 96, I imagine well over 100k right? What's the condition of the interior of the radiator? Perhaps it needs to be rodded or re-cored?

[Tragertt]

How many miles on the rig? As a 96, I imagine well over 100k right? What's the condition of the interior of the radiator? Perhaps it needs to be rodded or re-cored?

The Montero has 190k miles on it and the radiator seems to be beat up a little bit, I found a new one on rock auto for $60 so I think I will order it and take that out of the equation.

[off-roader]

The Montero has 190k miles on it and the radiator seems to be beat up a little bit, I found a new one on rock auto for $60 so I think I will order it and take that out of the equation.

Make sure it has metal tanks and not plastic ones. The cheap radiators have plastic ones. You can also find a decent used ones on car-part.com or at least one you can send out to be either rodded or re-cored at a good radiator shop. If re-coring one, it's also a good time to add an additional row when you have it re-cored. It's usually cheaper and just as effective as buying a new Mitsu Original part radiator.

[GrassCat]

Make sure the AC fan, the one in front of the radiator, comes on when you turn on your AC. It should also cycle on and off as needed.

I found a new one on rock auto for $60 so I think I will order it and take that out of the equation.

Don't buy a $60 radiator. Hell that must be a heater core.

[kuroi]

So the temp still rises when you have the ac on and your moving?

[Tragertt]

So the temp still rises when you have the ac on and your moving?

If I am drive then my montero starts to get hot after some time of driving. I am going to replace the radiator and see if that helps.

[off-roader]

If I am drive then my montero starts to get hot after some time of driving. I am going to replace the radiator and see if that helps.

Don't buy an aftermarket radiator unless it has metal tanks (many have plastic tanks). Also it's usually far cheaper to have the radiator 'rodded' and just as effective as buying a new one. Rodding a radiator entails removing the top and bottom tanks then running a steel rod through each of the holes in the cooling fins to remove the built up scaling that will reduce coolant flow. Once the flow is restored, your radiator should cool good as new.

Alternatively you can likely purchase a used radiator in good condition for less than half a new metal radiator from a parts yard. Just ask them to ensure the insides are clear of any deposits.