+1. I had the same thing happen on my truck. Added some coolant and it was gone.

 

Can it be low on coolant even if the reservoir is full?

 

Yes, if there's a big enough air bubble that hasn't been bled properly.

 

Low coolant light was intermittent today. Checked the level this evening, was down about an inch below the full line. This happened a few months ago, I obviously have a slow leak somewhere. But, no signs of a leak anywhere under the hood or under the truck.

 

Pressure tester can be rented and a vacuum kit can help pull trapped air bubbles.

 

park snout up on a hill and rev it for a while. bubbles will usually work themselves out that way.

you need to find that leak though. Could be a water pump, cracked head, or a bad head gasket. Ask me how I know...

2000 5.3 - Coolant in oil

 

My GMT 400's do this as well. Air in the heater core, you are hearing the coolant rushing to replace it.

peace
Hog

 

How many miles when you changed the heads?

 

i think it was around 135k. It has about 160 on it now with no problems. it used to use a quart of oil between changes, but it doesn't do that anymore either.