Engine Running and No Coolant Cap (Safe?)

The cap prevents your system from building pressure.
I wouldn't drive my truck far without a cap.

Probably idle the truck so air pockets will flow out of system.

 

That’s after you refill coolant. In order to bleed system of air pockets. Sometimes there Is also a bleeder screw (Petcockinstalled at high point of top hose/ steel tubing to radiator.If so crack it open also till it quits bubbling. Give it 1 or even 2 hrs watching and topping off. It may take up to 1 even 2 more gallons before it’s done.Keep at least a gallon in Truck just in case after you think you’ve got all the air out. First time I learned from having to add almost 2 gallons over 3 hrs or so on My 300 mile trip!! Kept shutting down Lol It can take a long time to get trapped air out be patient 2-3 hrs cap off at idle should do it for sure.

 

Remember to start your APU, if you have one, and also make so to run the heater to get the air out of those as well.

 

I didn't either when I did my rebuild. I took it for a ride and went into a panic when I saw the reservoir was almost empty! !

 

Radiator cap is everything, pressurizes a normal coolant system. When the cap goes bad and does not adequately work, then you can have a constant series of puzzling overheats.

Refilling or filling new coolant is a very important time. Hopefully you get it all in eventually with that cap loose.

It's relatively easier and faster to get the air out of a ordinary V8 engine and radiator than it is to get it out of a big truck. That will take a while.

 

Vacuum filling is the only way to go for filling cooling systems. If you vacuum fill for sure there are no air pockets. Run the engine up to temp and cold fill to the cold full mark after a cold soaking the am. No muss ,no fuss. Any vehicle, any engine.

 

Please elaborate. Keep cap off I assume let gravity do its work? I’m reminded of gravity bled brakes on cars never done it doesn’t seem like it would even work yet Some Master Techs swear by it.

 

UView | Cooling | Airlift™ Kit

This is my preferred tool but a quick search will reveal many other choices. Pulls vacuum on the system using venturie effect with compressed air. Pulls coolant into the system once vacuum is achieved. No need to burp or bleed of air while running the engine. Large systems can take 2 draws to fill.