weird low coolant issue?

[CEN2MENTAL95]

on my 01 tahoe with 127k.....

sometimes I'll be driving and the low coolant light comes on....temp never creeps above 1 notch below half (normal) and the coolant level "appears" fine...but what is fine for these trucks?

at cold or when the engine is off, coolant overflow is half filled. once truck is running and/or warmed up the level drops down in half. once turned off or cold, back up to half level.

no coolant leaks visible. system was pressure tested. no puddles on ground.

any ideas? bad sensor?

 

[Rivieraracing]

on my 01 tahoe with 127k.....

sometimes I'll be driving and the low coolant light comes on....temp never creeps above 1 notch below half (normal) and the coolant level "appears" fine...but what is fine for these trucks?

at cold or when the engine is off, coolant overflow is half filled. once truck is running and/or warmed up the level drops down in half. once turned off or cold, back up to half level.

no coolant leaks visible. system was pressure tested. no puddles on ground.

any ideas? bad sensor?

Sounds like what I was experiencing right before my water pump crapped out! Make sure to top off the coolant resevoir to where it needs to be and see how long it takes for it to come back down to set off the sensor!

 

[CEN2MENTAL95]

Sounds like what I was experiencing right before my water pump crapped out! Make sure to top off the coolant resevoir to where it needs to be and see how long it takes for it to come back down to set off the sensor!

but when the truck is off, it stays at half...if i fill it (which I have) it becomes overfilled.

It only drops down once running. can't fill while running because its pressurized?

 

[Rivieraracing]

There are marks on the resevoir, where is the level sitting at in the morning when it's been sitting overnight? If it's showing that you need to add coolant, then be sure to do it then!! And be sure that's what it's actually reading by opening up the cap at that time (since it's cold) to confirm the level since these tanks get dirty inside and sometimes have a fake level line due to residue (mines bad like that).
If the level is fine at that time, then I'd say the tank sensor is haywire or just bad, otherwise if you level is indeed low, the the sensor is working and it might be a start of another problem!

 

[CEN2MENTAL95]

ok ok....let me clarify:

the coolant level in the overflow is at half when the truck is completely cold (overnight)

once warmed up, the level drops in half (to 1/4)....once the truck goes cold again its back up to full half way

(checked for dirty-tank is pretty clean)

 

[TheFuzz]

Like he said, there are marks on the tank. Does it "look" half full, or is it half full compared to the marks?

The coolant level fluctuating is completely normal. The system only builds up pressure when the truck is running, and only then is coolant circulating through all of the passages in the block, the radiator, trans cooler ect. This causes the level in the reservoir to change because all of that coolant is actually circulating through the motor doing it's job. The reservoir is just that - a reservoir.

If the level is low, fill it according to the marks on the tank. If the level is ok, leave it alone.

 

[CEN2MENTAL95]

Like he said, there are marks on the tank. Does it "look" half full, or is it half full compared to the marks?

the tank itself when cold is half filled (or up to the fill mark)

 

[Rivieraracing]

the tank itself when cold is half filled (or up to the fill mark)

Well, if its cold and at the fill mark, fill it up to the full mark and see how long it takes to drop back down to the fill mark!! More than likely you are losing coolant somewhere if you are topping it off and it keeps dropping!

Also, if you park in a garage at night, take some clean cardboard and place it on the ground under the rig overnight and see if you see any spots the next morning, or after driving somewhere!

 

[bigbird189]

Well my yukon did the same thing then my water pump took a dump on me. no problems since.

 

[afpj]

on my 01 tahoe with 127k.....

sometimes I'll be driving and the low coolant light comes on....temp never creeps above 1 notch below half (normal) and the coolant level "appears" fine...but what is fine for these trucks?

at cold or when the engine is off, coolant overflow is half filled. once truck is running and/or warmed up the level drops down in half. once turned off or cold, back up to half level.

no coolant leaks visible. system was pressure tested. no puddles on ground.

any ideas? bad sensor?

That's odd, on our 02 yuk, if the level is at the "full cold" mark, which is at the seam about half way on the reservoir, then once its warmed up the level is higher by about 3/4 inch. Only when the engine is revved to about 2000-2500 rpm do I see the level drop, but then comes back up at idle. None of my heater controls are on though...do you have any of the temp settings raised, like for the back seats? I always thought the coolant level in the resevoir rises as the engine is warmed up. The only time I experienced the coolant level dropping (aside from the water pump going) after warmup was after I changed out radiator hoses and the system wasn't completely "burped".