Overheating Question - Help Me with my Logic

Need some clarity on how I fixed an overheating problem:

My truck started overheating and I immediately pulled over, let it cool down and got it back home.

I checked the reservoir and it appeared to be empty (I have not seen any leaking fluid nor remember filling it up so I believe I’m the idiot here). I added fluid and attempted to burp the system without my trusty funnel. At first, it started overheating again, so I let it cool. Next time I started it up, I heard what sounded to be a airbubble and then the temp started holding just left of center on the coolside (awesome!).

I’m trying to decipher the logic of what happened and if I should still take it in. Do you think there was trapped air that was sucked in from the empty system that was keeping the thermostat closed? When it finally opened after that air left, it started cooling properly?


If the resvoir was not empty and you had not serviced the system recently, than there should not have been air in the system. I would change the thermostat with a fail open model and a new radiator cap.

I think the reservoir was empty. I should have been more specific in my wording…what I saw in teh bottom of the reservoir was miniscule and the radiator appeared to be empty based on how much fluid I was able to put in…if it was empty, would air possibly be in the system?

Without any vehicle info…when cold, check the levels in the radiator if it has a cap, and the reservoir. Top up the radiator, and fill the reservoir to its recommended level, and drive the car for several warmup/cooldown cycles. Then, again when cold, check the coolant levels. The reservoir level may or not have changed. What has happened to the radiator coolant level?
Let us know.

Vehicle Info: 2006 Dodge Ram 1500 5.7

The empty reservoir is a concern, but the radiator coolant level after driving the truck several times, cold to warmed up to cold is very important.

I’d replace the cap. It’s just too easy and cheap a fix to ignore.

You’re now entering “overheating never-never land.” We’ve all been there. Keep an eye on the reservoir and temp gauge. I fear your saga is far from over.

sethmac-let us know what you have done, and its effect.

When the engine is cold, fill the radiator to the top and the overflow tank half way and see what happens…

My concern would be where the coolant went to in the first place. Got to be a leak somewhere. I think a pressure test would be in order. You don’t necessarily see fluid leaking on the ground all the time when you have a leak. Look for residue in all the likely places like tank, radiator, water pump, hoses, etc.

To answer your original question, yes, air in the cooling system can cause overheating.

If there’s air in the cooling system and this air gets to the water pump the water pump can cavitate. This means the air is causing the water pump to create bubbles. If enough bubbles form at the water pump the water pump stops circulating coolant thru the cooling system. Then once the coolant stalls or stops flowing, the coolant in the engine begins to overheat.


I had a 60’s Ford that would sometimes overheat for a minute or so, then I’d hear a very loud “click” and a rushing-water/steam sound, and then the overheating would stop straight away. I discovered the thermostat was sticking shut, until it got hot enough to overcome the friction, then it would release to fully open with full force, the thermostat spring force slamming the valve open very fast was the cause of the “click”.