Burping a radiator, question

Caps have a pressure rating. It should say on the top, what it is. Old Trucks are usually 10 lbs. or less. Newer Trucks, I believe run a higher rated cap. Since they run hotter, and higher pressure, raises the boiling point of the coolant. First thing to do is check that the cap is the right one for your Truck. (has the proper rating for pressure, ). The cap can be easily tested. Auto parts stores will loan you the kit, if needed. They call it a closed system, I believe, having an expansion tank. Similar to modern automobiles. If you left cap loose, overnight ( to vent) or whenever for a while, and the hose no longer collapses, I would suspect the cap. Since it’s a common symptom of a bad cap. In your case though, I really don’t know enough about how it works. Maybe it is just trapped air causing it, since it’s a closed system? Leaving the cap loose, and running it, eventually, all the air will work its way out. Apparently this is a problem, as some, notably Rawz advocates running 0 coolant pressure. Seems to Me though, that might cause boiling of coolant, and cavitation/ pitting in the engine, in theory anyway. Real world operation, Who knows? A little more research may be needed.

 

Did the coolant level drop then? In the resivior? Below the low coolant sensor? Need to top it off if so.

 

I’m not sure, but I think if the systems full, the level doesn’t drop when the stats open.Maybe on initial fill, but when it’s all full, normal operation, the system bypasses stats, till they open. The level in reservoir gets higher, due to heat expansion. Then after shutdown, it cools, and level goes down.Proper pressure and venting operation of the cap, allows it to hold pressure and vent enough,as needed,to allow coolant to flow back into radiator, as it compresses back to the original volume, a sealed system, keeping air out.My car boiled over last summer, while idling, one of two cooling fans not working, I must have been low on coolant. It took a long time to get it right again.I thought for sure my thermostat was bad. I would talk to a mechanic, at the dealer, if you go to get a new cap. I’m wondering what started all this. I assumed you had flushed the radiator, or replaced some parts, and all was well beforehand. Have you been adding coolant? Is it disappearing?

 

Freightliner

 

you don't really want cheap, you want correct OEM parts. the cheaper ones are "universal fit all" parts.

and as such, may or may not have a by pass hole in it or the correct spring pressure.

 

We did that on one of a thousand hills on our farm. Stick the think uphill and wait a while.