My 2000 Chevy Suburban (Vortec 5.3 engine) occasionally flashes a
trouble alarm that the coolant level is low. By occasionally, I mean
maybe a total of 5 times during the last 6 months. It occurs after an
hour or more of driving
and it doesn't seem to be affected by ambient temp. or engine temp.
Engine temp always runs normal. Last week it came on for the first time
in several months. When the
alarm comes on. I have verified that the level is low. I looked at my
owner's manual and to my surprise, it suggests that the level should
fall slightly when the car reaches operating temp. Yesterday, I
verified that this does occur although it fell only about a half inch
or so. Why should the level fall? The only answer I can think of is
that the hoses expand when they are hot and pressurized. I believed
that explanation more when I saw the level go back to the COLD normal
when I cracked the cap and let the pressure subside. I
have never added coolant in the 2+ years that I have owned it. This
past June I made a 4000 mile trip and the alarm never came on.
Similarly, in September I was a hurricane Rita evacuee stuck in endless
traffic jams and the alarm never came on.
So, my questions are:
1. What could cause the level to occasionally and unpredictably
extra low when the engine warms up?
2. Why does the level fall at all with increasing engine