Engine temperature gauge reading on 2004 GMC Yukon has climbed to extremely high level but engine does not appear to be overheating-top rad hose is warm, coolant is not high but is present. Vehicle is acting normally. Heater is working correctly and the idiot light panel says nothing about coolant temperature.

I'll put my bets on a faulty gage...but that's just me.

So you have an overheating problem. Check the coolant level in the radiator, check for coolant leaks with engine running (fill radiator if necessary), check temperature of upper rad. hose as engine gets hot (this checks for thermostat operation). Could also be a clogged radiator, bad fan clutch, or blown head gasket.

YOU NEED BLEED AIR OUT THE COOLING SYSTEM.WAIT TO ENGINE COOL DOWN.YOUR VECHICLE YOU HAVE TO POUR COOLANT IN THE COOLANT OVERFLOW JUG UNTIL COOLANT LEVEL STAY AT THE FULL COLD MARK.THEN START ENGINE LET IT IDLE A FEW MINUTES WATCH COOLANT IN THE OVERFLOW JUG WHEN IT DROPS ADD MORE COOLANT UNTIL COOLANT LEVEL STAY AT FULL COLD MARK.WHEN COOLANT LEVEL STOP DROPPING IN OVERFLOW JUG.SCREW RADIATOR CAP BACK ON OVERFLOW JUG WATCH ENGINE COOLANT TEMPERATURE GAUGE AS COOLANT TEMPERATURE START CLIMBING TURN OFF ENGINE LET IT SET A WHILE KEEP FROM GETTING SCALDED.TAKE LARGE RAG PLACE OVER COOLANT OVERFLOW JUG CAP SLOWLY OPEN RADIATOR CAP A LITTLE AT A TIME UNTIL PRESSURE RELEASE.REMOVE OVER FLOW JUG CAP.ADD MORE COOLANT UNTIL COOLANT LEVEL AT THE FUL COLD MARK ON THE OVERFLOW JUG.THEN SCREW CAP BACK ON THE OVERFLOW JUG.START ENGINE LET IT IDLE AGAIN WATCH ENGINE COOLANT TEMPERATURE GAUGE WHEN TEMPERATURE GAUGE START CLIMBING.TURN OFF ENGINE WAIT A WHILE.CHECK COOLANT LEVEL IN THE OVER FLOW JUG.DO THIS PROCEDURE UNTIL THE COOLANT LEVEL IN THE COOLANT OVERFLOW JUG STOP DROPPING AND STAY AT FULL COLD MARK,WHEN THE TOP RADIATOR HOSE GET HOT THERMOSTAT OPENING AIR IS OUT THE COOLANT SYSTEM. WHEN ENGINE COOLS DOWN.CHECK COOLANT OVERFLOW JUG COOLANT MUST BE IN THE COOLANT OVER FLOW JUG AT THE FULL COLD MARK WHEN ENGINE COLD. DONT .DONT OVERFILL COOLANT OVERFLOW JUG.KEEP COOLANT IN THE OVERFLOW JUG IF YOU LET COOLANT OVERFLOW JUG RUN DRY AIR WILL BE DRAW IN COOLANT SYSTEM CAUSE ENGINE TO OVERHEAT.

WELL YOU NEED TO DRAIN COOLANT LEVEL BELOW THERMOSTAT LEVEL.YOU HAVE TO DISCONNECT MAF SENSOR LOOSEN AIRDUCT 2 LARGE CLAMPS LOOSEN REMOVE 4 SCREWS TO AIR FILTER COVER LIFT UP REMOVE COVER. THEN REMOVE AIR FILTER AND HOUSING, FIRST DISCONNECT MAF SENSOR.YOU HAVE TO DISCONNECT THROTTLE CABLE AND SHIFT CABLE.YOU HAVE TO DISCONNECT REMOVE THROTTLE BODY COOLANT HOSES DISCONNECT IDLE SPEED CONTROL VALVE CONNECTOR AND DISCONNECT TPS SENSOR CONNECTOR. THEN REMOVE THROTTLE BODY ASSEMBLY. YOU NEED TO BUY NEW THROTTLE BODY COOLANT HOSES AND NEW THROTTLE BODY GASKET FOLLOW TOP COOLANT HOSE TO ENGINE BLOCK.NOW YOU SEE CAN AND REMOVE THE THERMOSTAT HOUSING REPLACE THE THERMOSTAT.BESURE TO HAVE EXTRA COOLANT ON HAND.BLEED COOLANT SYSTEM WHEN DONE.TO BLEED COOLANT SYSTEM REMOVE RADIATOR CAP ON OVERFLOW JUG.THEN OPEN BLEED SCREW ON THE WATER PUMP BYPASS HOSE PIPE JUST A LITTLE.POUR COOLANT IN THE OVERFLOW JUG UNTIL LEVEL STOP DROPPING.STOP AT COLD MARK ON JUG.CLOSE BLEEDER SCREW ON WATER PUMP BYPASS HOSE PIPE.CRANK VECHICLE CHECK FOR LEAKS. START UP ENGINE LET IDLE FEW MINUTES THEN CHECK COOLANT LEVEL ADD MORE UNTIL UNTIL LEVEL STOP DROPPING.PUT RADIATOR CAP BACK ON OVERFLOW RESERVOIR. LET ENGINE IDLE WATCH COOLANT TEMPERATURE GAUGE.WHEN GAUGE START CLIMBING. TURN OFF ENGINE WAIT FEW MINUTES TAKE A LARGE RAG OPEN RADIATOR JUST A LITTLE YOU HEAR HISS NOISE.WHEN PRESSURE STABILIZE DONT GET SCALDED BECAREFUL.OPEN CAP LITTLE MORE.IF COOLANT PRESSURE STILL BOILS OUT WAIT 20 MINUTES ADD MORE COOLANT TO RADIATOR OVER FLOW WHEN COOLANT LEVEL STOP DROPPING.PUT RADIATOR CAP BACK ON START VECHICLE UP LET IDLE UNTIL THERMOSTAT OPEN. THEN FEEL TOP RADIATOR HOSE FEELS HOT THERMOSTAT OPEN WATCH TEMPERATURE GAUGE.IF GAUGE TEMP START CLIMBING TURN OFF ENGINE WAIT A WHILE.CHECK AND ADD MORE COOLANT.WHEN THE ENGINE CAN IDLE TEMP GAUGE STOP CLIMBING YOU HAVE BLEED COOLANT SYSTEM.KEEP CHECK ON COOLANT LEVEL.

Start it cold with rad cap off, and heater on high heat, and let it run until you see increased flow in radiator, indicating thermostat opened & engine reached operating temperature. Rev engine slightly every once in a while and hold it there for 10-20 seconds, just to help purge air better/faster. Watch rad flow again, and wait until you see increased flow 3 or 4 times. Then top up coolant in rad to an inch or 2 from top of rad, and put cap back on. Top up return bottle to appropriate level on bottle & then try it again. If it still heats up, get back to me. Does it overheat at all times? Rad fan is good i take it?

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.

it sound like u have air in your radiator.there is some bolds that u can unscrew and let the air out hope this helps

With engine cold, remove rad cap & check level in rad. Top it up if needed to 1 or 2 inches from top. Start engine, turn heater on (not defrost) and observe coolant level as engine warms up, add if necessary. Radiator fan should be off, and only come on when engine reaches normal operating temperature, for a short time, then shut off again. Let it run until that happens about 3 times, then put rad cap back on. If temperature gauge climbs up over normal toward hot, too much, shut it off. Do you now have heat? Is rad fan acting as I described? Let me know.

check fluid level if full remove rad cap when car is cold and run while looking at fluid in rad if it is circulating you should see it moving if it does'nt move after car warms up thermostat needs to be replaced also check to see if fan is working properly and check the reputation of your mechanic some are not always honest

I think that you can install a thermostat backwards and it may not work correctly; just make sure. I would open the radiator and run the car to operating temperature and see if the water level drops in the radiator. If it does than the thermostat is opening properly. If you have a cold water still in the radiator, than it means that coolant isn't circulating properly. It could possibly be an issue somewhere in the lower hose.