Running hot

It sounds like both or one radiator cooling fan motor is not working. Here is a guide to help walk you though the steps to replace it.

https://www.2carpros.com/articles/replace-electric-fan-motor

Start by checking the fuses and relays.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

and

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here are the cooling fan wiring and fuse with replay locations

Check out the diagrams (Below)

Please let us know what you find. We are interested to see what it is.

Cheers

Good to hear, please use 2CarPros anytime we are here to help.

That is a very common symptom and can be caused by an inoperative electric radiator fan motor. You need plenty of air flow through the radiator to cool it. That air flow takes place naturally when the vehicle is moving. The fan is not needed when natural air flow is enough to cool the radiator. You don't usually have natural air flow when the vehicle is standing still, unless it's a windy day. That's when the electric fan gets switched on when the coolant temperature gets too hot.

There are other things that can cause an engine to only overheat at highway speeds, and there are things that can cause overheating at any time or speed. For what you described, the fan is the logical place to start looking.

Hello,

It sounds like you have a blown head gasket. To be sure please check this guide:

https://www.2carpros.com/articles/head-gasket-blown-test

Please run down these guides and report back.

If the cylinder head gasket is not leaking, where is that air coming from? Oil and coolant mixing is by far the least common way a cylinder head gasket will leak because there is so little difference in pressures between the passages for those two systems. Gases in the combustion chamber will be at hundreds of pounds of pressure. It takes a lot for the gasket to seal that.

The chemical test Ken is referring to involves drawing air from the radiator, while the engine is running, through a glass cylinder partially-filled with a special dark blue test fluid. If it turns bright yellow, that is positive for combustion gases sneaking into the cooling system. It doesn't have anything to do with engine oil.

About half of these leaks also let coolant go into the combustion chamber from the vacuum during the intake stroke. That will cause white smoke from the tail pipe. Don't be alarmed if you see steam at the tail pipe, or clear water dripping from the tail pipe or the drain hole in the bottom of the muffler. Water vapor is a byproduct of a properly-working catalytic converter. The clue here is the coolant level will be going down in the reservoir.

Head gasket leaks that affect anything related to engine oil are extremely uncommon. Your comment about checking for leaks after the water pump was replaced suggests the mechanic checked for external coolant leaks, which would make sense. We aren't interested in that either. I also just stated, "about half of these leaks also let coolant go into the combustion chamber from the vacuum during the intake stroke". That means about half of the time you will not lose coolant when the head gasket is leaking. That is what you observed.

The link to the article that shows the chemical test that needs to be performed. If that test comes up negative for combustion gases, there is no air getting into the cooling system. The engineers at GM left the radiator caps off a lot of their radiators. This test is done then at the reservoir cap.

Sometimes when a head gasket goes bad it wont leak coolant into the engine. Please try the test and get back to us.

When does this happen? If the temperature remains normal while you're on the highway, that is evidence the radiator fan isn't running. It is only needed at low speeds or when stopped in traffic, otherwise normal air flow is enough to cool the radiator.