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1. Make sure the electric radiator fan(s) is kicking in when the coolant temperature gets hot. If not that will be part of the problem and if the temperature sensor/switch is faulty the fans may not operate.
2. You may have a restriction in the cooling system that is significantly retarding the flow of coolant through the engine coolant passages or through the radiator. This can be caused by a build up of debris in the system so you cannot achieve optimum coolant flow.
3. You may have a combustion leak via a failed cylinder head gasket into the cooling system. This will cause hot combustion gasses to flow from the cylinder into the cooling system and the coolant will overheat. Bubbles showing up in the cooling system is a possible indication of that. A leak down test will show this up. This involves blowing compressed air into the cylinders one by one through the spark plug openings. If air enters the cooling system in this test bubbles will appear in the coolant and it is a sign of a failed cylinder head gasket and that combustion gasses are able to escape into the cooling system when the engine is running.
4. THE rough idle may be a low RPM miss fire in one or more cylinders. You need to have the vehicle scanned to see what fault codes the computer is generating. If you have rough idle once the engine has warmed up there will be one or more fault codes being generated. Once scanned and all the fault codes are found, the cause of the fault codes can be investigated and the problem fixed.
5. Do not hesitate to have the problem of the overheating checked out. Running the car with the engine overheating WILL cause expensive engine damage many times more than it will cost to fix the problem now. If you have been running the engine frequently in an overheated condition you may well have already caused failure of the cylinder head gasket but I hope this is not the case. Running the engine overheated can also cause the cylinder head to warp and crack. These are expensive engine repairs you definitely want to avoid.
6. You did not indicate the year, model of vehicle and engine type you have. Please provide this information if you have future questions as this normally has a direct bearing on the content of answers people are able to provide.
Could be air in cooling system. Check radiator cap on motor. Open when cool, fill to top and start car. Pump hoses to get air out. While running keep filling when thermostat opens. Rev engine if you'd like to quicken the process. When you can get anymore coolant it put top back on. Check for leaks!
CAR OVERHEATING FIRST CHECK FOR LOW COOLANT IN THE RADIATOR COOLANT OVERFLOW JUG.IF COOLANT LEVEL IN OVERFLOW JUG LOW REFILL ADD COOLANT BACK TO THE FULL COLD MARK.PUT RADAITOR CAP ON COOLANT OVERFLOW JUG START ENGINE LET IT IDLE UNTIL IT OPERATING TEMPERATURE.MAKE SURE TOP RADIATOR HOSE GETTING HOT WHILE ENGINE WARM UP.IF TOP RADIATOR HOSE DONT GET HOT WHILE ENGINE IDLING YOUR THERMOSTAT COULD BE STUCK CLOSE CAUSING CAR TO OVERHEAT.IF TOP HOSE IS GETTING HOT.CHECK FOR COOLANT LEAKS CHECK TOP RADIATOR HOSE AND BOTTOM RADIATOR HOSE FOR LEAKS.CHECK FOR LEAKS AT THE RADIATOR CORES AND PLASTIC SIDE CONTAINERS.IF ALL IS GOOD ENGINE OVERHEATING WHILE IN A LONG TRAFFIC LINE, COOLANT FANS NOT COMING ON.COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR BLOWN COOLING FAN FUSE OR RELAY.COULD HAVE PCM FAULT.MAKE COOLING FAN ELECTRICAL CONNECTORS AND WIRING NOT DAMAGE OR BROKEN.
ENGINE NOT GOING TO START IF GET TOO HOT FIRST THING I WOULD REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP THEN ADD COOLANT UNTIL COOLANT LEVEL CORRECT THATS WHEN THERMOSTAT OPEN UP AND TOP HOSE HOT.CHECK FOR LEAKING RADIATOR HOSES CHECK TOP RADIATOR HOSE CHECK BOTTOM RADIATOR HOSE.CHECK FOR LEAKS AROUND THE RADIATOR LOOK DOWN BELOW COOLANTS FANS CHECK FOR LEAKS AT RADIATOR CORES OR LEAKS AT THE RADIATOR PLASTIC SIDE CONTAINERS. CHECK FOR LEAKS AT WATER PUMP WEEP HOLE AND CHECK FOR LEAKS AT THE HEATER HOSES AROUND ENGINE BLOCK TO THE HEATER CORE HOSES. THERE IS A REASON CAR OVERHEAT.IF CAR OVERHEAT WHILE DRIVING YOU HAVE FAULTY THERMOSTAT OR LEAKING OUT COOLANT OR BLOWN HEAD GASKET.IF ENGINE OVER HEAT WHILE SITTING DURING A LONG IDLING PERIOD.YOU COULD HAVE FAULTY COOLANT TEMPERATURE SENSOR OR FAULTY COOLING FAN FUSE OR RELAY.HOT WIRE COOLANT TO SEE IF IT RUNS IF NO REPLACE FAN MOTOR. IF YES FAN MOTOR COULD HAVE FAULTY WIRE OR PCM FAILURE. CHECK ENGINE CRANKCASE IF OIL LOOKS LIKE MILK SHAKE ENGINE HEAD GASKET LEAKING.
The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system. There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line. With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating. If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage. The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there. Also note that the cooling fans don't come on until the coolant temperature hits around 225 degrees. During normal highway driving the fans will very rarely come on(if at all) due to constant air flow through the radiator.They will only usually come on in heavy traffic conditions on a hot day. But......if you have the Air Con switched on, the fans will run all of the time.
Look at the coolant and the oil. If either one has the other mixed into it, it is probably the head gasket. If not, it mat still be the head gasket but try this first:
Check the car visually for any cooling system leaks. Make sure that the overflow tank tube is not obstructed and the tank itself is not cracked or leaking and the that the cap is in good shape. With the radiator cap off, start the car and let it run, top off the radiator with coolant as necessary. Grab the upper radiator hose every minute or so while monitoring the cars temp. gauge also. The hose should warm up slowly if the thermostat is working and eventually become solid to the touch from pressure. Once it opens, bring up the rpm of the engine(1500 to 1800 rpm) while you top off the cooling system, install the rad. cap THEN let the idle drop down. Feel the upper hose for air bubbles. If they are present, shut the car off, let cool and repeat the process. You may have air bubbles in the system, test and/or replace the radiator cap before you test the system. I hope that works for you.
Presurize system with radiator cap on to see if you are holding 10 to 13 LB pressure as high as 17 LB. Get new radiator cap for your radiator. Check for a slow leak at pump hose thermostat conection , is it wet ?
Do you have a Summer Thermostat ?
Vitally
When driving down highway only, it overheats? When running steady, I take it you mean, sitting idling? If it's only overheating at highway speeds, and all else has been checked out & is o.k., I'd take a close look at rad hoses for soft spots (easy to squeeze) that may be causing hoses to collapse at highway speeds & restricting flow of cooling system. Another thing to try is, turn your heater on high fan & high temperature when it starts to heat up & see if temperature gauge goes down (cooler) at all. If it does, then rad not doing it's job properly.
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