1989 GMC C1500 5.0L V8 -
after replacing the thermostat twice and the temp sensor, still have
this problem and not knowledgable enough to resolve - please help!
after running for a bit temp will rise (temp guage indicates) to ~195
deg (thermostat rating) and then after (I assume) the thermostat opens
the temp will drop to ~160 and stabilize there regardless how long or
hard the engine is run...
I am at a loss... I do have a higher cooling capacity radiator than the
one that came stock but wouldn't think that was an issue as I thought
the thermostat should still regulate the block temp. regardless... I
haven't tried replacing the radiator cap but will tonight... is there
any possibility that the cap is allowing the system to overpressurize
and not allowing the thermostat to close once opened?... just grasping
at straws here... please help!
I am having the same exact problem on my '05 gmc sierra. It has always ran at about 190 - 195, i noticed today that when i started the truck (already warmed up) the temp went to 190. Then after about a minute or so, it drops to the bottom temp of 160 and stays there. Does this sound like the thermostat is bad or is the gauge / sending unit going bad?
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Is your 3800 producing normal heat? If so, the temp sensor is probably bad...If not, try replacing the radiator cap...if your system has air trapped inside, it usually runs hot, not cold...the heat is the key to functioning properly for you...Your radiator is a 4 stage huge system that normally cools very well...if you have heat, I still think your temp sensor is bad...ask to see one at your parts store, will help you to locate it. Hope this helps.
you might want to check the wires going to the temperature sensor on the engine make sure it hasnt rubbed the protective coating off, this can give you a false reading, the safest way is to put a manual gauge in place of the temperature sensor and run engine to make sure the engine is not overheating. You can pick up a cheap manual temp gauge at your local parts store and install the temperature probe into the hole where the temp sensor was located and run the engine. It sounds like you have a guage malfunction. But is better to be safe than sorry.
The thermostat is located on the driver's side of the engine. It is difficult to see, but it is behind the alternator. The lower radiator hose goes to a metal tube, that is part of the thermostat housing. Below is a picture of thermostat and temp sensor location (alternator removed).
You'll find that this is actually your thermostat, not the actual sensor itself. Your thermostat is sticking open causing it to run too cool. Replace the thermostat, and that light will go out. I went a year with this problem, replaced the sensor twice, light would still go on. The bad thermostat was causing bad readings by the sensor. Very common problem for Envoys and Trailblazers.
There is the coolant sensor that tells the computer the temp,and the computer sends a signal to the cooling fan relays,and the relay turns the cooling fans on,and off,if the system is low on coolant,or has air in the cooling system,then the cooling fans would not come on,or the sensor is bad,if this was at all helpful,please rate,thank you.
V6 2.8L top right rear of engine. Fan also turns on through A/C pressure switch and coolant temperature sensor, but these should operate independent of the coolant temp switch.
V8 5.0L and 5.7L (Heavy Duty) lower right rear of engine above starter.
Base model V8 uses the coolant sensor (top right of engine) and A/C pressure switches (lower right corner of eng compartment on A/C line to turn on the cooling fan. Fan is energized on all applications through the cooling fan relay.
Drain the coolant (left lower side of the radiator) Follow the upper radiator hose to the engine, at the end of the hose is a metal housing, held down with 2 bolts, or 1 bolt and 1 stud. There may be wires going to one of the bolts, be sure these go back on. After taking the 2 bolts out, lift up the housing and the thermostat will be right there. Clean the old gasket from the manifold and the water outlet housing. Now install the thermostat, then the gasket. and torque down the bolts evenly. about 25-30 ft pounds. fill the radiator until about 2 inches below the filler neck, and start the engine, now keep putting coolant in to keep it 2 inches below the radiator neck, and let it warm up until you see coolant moving in the radiator, now fill it to the top and fill the coolant bottle to the cold mark. Its a good time to replace the radiator cap also. Good Luck.
2000 LS cooling system is a very tough system to diagnosis. Any kind of air in system will totally stop the flow and cause it to heat.That is the reason it has 2 places to bleed the air from the system.The one at the engine where the upper hose connects and one beside the brake booster near the degas bottle(rubber tube with a screw end).
The cooling fan is also hydraulic and has it's own power steering pump. The good thing about this system is that it uses a cylinder head temp sensor that measures the metal temp and not engine coolant temp. When the PCM sees the CHT reach a certain temp it will start shutting down 4 cylinders at a time and use these cylinders as actual air pumps to help cool the engine down.If this does not work it will then shut the engine down totally until the temps come back down.
The most common problems we see are thermostats,crack degas bottle,or a leak somewhere,and of course air in the system. Have not seen a cracked head yet however did see one that pushed the plug out of the cooling port in the head but this also filled the oil with coolant.
Have also seen cooling fans that would not work until PCM demmanded high speed,caused by a weak power steering pump.