Weird Cooling Issue

[gbsharon]

Did some basic maintenance on the truck today (plugs). While I had the hood popped I decided to top off the coolant reservoir. It was low- below the cold. I don't think the truck is leaking coolant but it is a lot colder than when i filled it previously. Anyways, filled it up to cold while truck was cold. Now, truck coolant temp seems to be fluctuating a lot. Before, always held at a tick above the 1/4 mark. Now, it always settles there but it heats up really quickly. For example, it will be normal and ill punch it for a few seconds. The needle will move up to 210 then settle back down to normal. Is this normal for after filling up reservoir? I had previously almost never seen the needle move except when engine warmed from zero to normal operating temp.

 

[beardeddummy]

You need to do a leak down and compression test. my temp Guage did something very similar to that when I cracked the heads. I had a temp Guage that acted like a boost guage.

 

[gbsharon]

Interesting- actually had a compression test done earlier this week for an unrelated issue and it came back good. Could this be something to do with air in the system?