Overheats on hwy. Radiator fan does not engage after overheating

Two cooling fans controlled by three relay's . If only one fan is working ,that could be a problem .
Coolant Level Sensor Description
The coolant level sensor monitors the coolant level in the cooling system and indicates if the coolant is low. This sensor is located at the base of the radiator surge tank and is not serviceable.
CHECK COOLANT LEVEL (2)
The IPC receives a discrete input from the engine coolant level switch. The engine coolant level switch is normally closed. When the engine coolant is low, the engine coolant level switch opens. When the IPC receives an open signal from the engine coolant level switch, the IPC displays the message on the DIC.

Relay Driven Dual Cooling Fan Diagnostics There are using a pontiac , by your cadillac is the same .

First, you must have a properly installed thermostat that is working correctly. Second, Northstar engines are notorious for air in the cooling system after draining and refilling - keep checking the purge tank level after overheating and after the cooling system cools down. Third, make sure your cooling fans are working correctly (relay, fuse, temperature sensor) - check to make sure both are running when it overheats. If all the above is correct, the problem will probably be blockage in the system (try a flush) or your water pump itself is failing.

Hello and welcome to FixYa!

If you have overheating problem, it can lead to multiple issues. You may be running on low coolant that's why the vehicle overheats. If that's the case, please add coolant and make sure that it sits on the right level, too much coolant can cause overheating too for coolant will overflow.

The vehicle may have a faulty or worn out radiator blower motor that's why it overheats. If that's the case then you will need a blower motor replacement to resolve the issue.

If the radiator is clogged with dirt and rusts this issue occurs too. The coolant doesn't flow normally on the cooling system if it's clogged. If that's the case, I strongly suggest that you have the radiator flushed to drain out dirt and rusts. If you think that the radiator served you enough then it's better to have it replaced.

Please do check the radiator hoses, If you have worn out hoses it can cause coolant leakage which can result to overheating. A tiny hole is good enough for the vehicle to overheat.

A faulty thermostat sensor can cause the issue too. If you have worn out thermostat, the fan may not trigger that's why the fan won't work when under stressed conditions. A blown radiator blower fuse can cause this issue too so I suggest that you check the radiator blower fuse and replace it when necessary.

Hope you find this information helpful enough and thank you for using FixYa! Have a good one!

Hello and welcome to FixYa!

If you have overheating problem, it can lead to multiple issues. You may be running on low coolant that's why the vehicle overheats. If that's the case, please add coolant and make sure that it sits on the right level, too much coolant can cause overheating too for coolant will overflow.

The vehicle may have a faulty or worn out radiator blower motor that's why it overheats. If that's the case then you will need a blower motor replacement to resolve the issue.

If the radiator is clogged with dirt and rusts this issue occurs too. The coolant doesn't flow normally on the cooling system if it's clogged. If that's the case, I strongly suggest that you have the radiator flushed to drain out dirt and rusts. If you think that the radiator served you enough then it's better to have it replaced.

Please do check the radiator hoses, If you have worn out hoses it can cause coolant leakage which can result to overheating. A tiny hole is good enough for the vehicle to overheat.

A faulty thermostat sensor can cause the issue too. If you have worn out thermostat, the fan may not trigger that's why the fan won't work when under stressed conditions. A blown radiator blower fuse can cause this issue too so I suggest that you check the radiator blower fuse and replace it when necessary. What causes the radiator blower fan fuse to blow? It's because of a failing radiator blower motor, If that's the case have the radiator blower fan motor replaced.

Hope you find this information helpful enough and thank you for using FixYa! Have a good one!

A head gasket leak is usually indicated (among other things) by continous overheating of the motor, and subsequent loss of coolant.
It can also be indicated by the presence of engine combustion gas bubbles in the coolant resevoir.
Ensure the coolant system has no external leaks, such as faulty hose/s, radiator etc.

Ensure motor tune or other motor mechanical condition is not the cause of overheating.
I assume the motor is actually running hot.

Check cooling fans are operating ok (as necessary when car warms up):- if not check
1) fuse,
2) relay operation,
3) heat sensor switch.

Check/replace the thermostat,
Check the coolant pressure cap is serviceable & of correct rating,
Ensure cooling system is correctly filled, bleed off any airlocks as necessary when re-filling,
Ensure radiator hose on suction side of waterpump is not collapsing at engine revs above idle (due softening),
If the motor has been severely overheated, the head gasket could be blown - look for combustion gas bubbles in the coolant resevoir.

replace that thermostat again...flush radiator any way...then see how it runs...

1. Remove air cleaner and duct assembly.
2. Drain the coolant.
1. Remove the engine mount struts.
2. Remove the cooling fans with the cooling fan shroud.
3. Remove the radiator upper hose from the radiator.
4. Remove the radiator lower hose from the radiator.
5. Disconnect the transaxle oil cooler lines from the radiator.
6. Remove the radiator brackets and bolts.
7. Remove the radiator. Installation Procedure
1. Install the radiator. Notice: Refer to Fastener Notice in Service Precautions.
1. Install the radiator brackets and bolts.
• Tighten the bolts to 24 Nm (18 ft. lbs.) .
1. Connect the transaxle oil cooler lines to the radiator.
2. Install the radiator upper hose to the radiator.
3. Install the radiator lower hose to the radiator.
4. Install the cooling fans with the cooling fan shroud.
5. Install the engine mount struts. Notice: When adding coolant, it is important that you use GM Goodwrench DEX-COOL (R) or HAVOLINE (R) DEX-COOL (R) coolant. If Coolant other than DEX-COOL (R) or HAVOLINE (R) DEX-COOL (R) is added to the system the engine coolant will require change sooner; at 50,000 km (30,000 mi) or 24 months.
6. Fill the cooling system.
7. Install the air cleaner and duct assembly.

try checking the hoses for blockage,and if not that make sure the fan is working right as it might be the fan cluch,or your water pump may have went out,best of luck

99 cadillac deville overheating put in new radiator,thermostat,waterpump. it stays cool at idle for a hour running.drivin about 15-30 minutes it overheats. is not using hardly any coolant to speak of.

maybe it is cloged up. also check the fans. and the thermastat. and temp sensor.