Coolant Level Dropping in Radiator

[eljefino]

This is a "hear hoofprints, think zebras" situation.

The overflow tank return is a siphon.

You need vacuum to run a siphon.

The little gap between the top of your antifreeze and the nipple for the hose to the overflow tank is the amount of vacuum you need for it to work, measured in inches of water column.

Resist all urges to check this for the period of time you've been checking it. Check it daily? Now check it weekly.

I bet you'll find the coolant in the same exact spot, and not have an issue, provided you've thoroughly burped the system.

 

[MSCH]

This is a "hear hoofprints, think zebras" situation.

The overflow tank return is a siphon.

You need vacuum to run a siphon.

The little gap between the top of your antifreeze and the nipple for the hose to the overflow tank is the amount of vacuum you need for it to work, measured in inches of water column.

Resist all urges to check this for the period of time you've been checking it. Check it daily? Now check it weekly.

I bet you'll find the coolant in the same exact spot, and not have an issue, provided you've thoroughly burped the system.

common sense aint so common... without reading any more of the replies I bet somebody has already suggested a bad head gasket.. not willin gto believe that the coolant level in one tank fluctuates with changes in pressure and temperature.. it can't be that simple.

 

[SHOZ]

One time I put a pressure gauge in the cooling system. At the time I had a 19 lb cap. But you could see the pressure rise to 19 lbs at about 200F and then the fans came on and cooled it down to 15 lbs or so. It cycled like that as long as as it idled.

I also put a clear hose to the overflow tank. If I cannot see coolant in the hose then there will be air in the radiator if I open it. If I can see a coolant and a bubble in the hose, it will be completely full. This is with the non pressurized over flows. The pressurized tanks are a whole world different animal and better IMHO.

 

[ripcord]

Get a pressure release cap with a lever. After driving, pop the hood and release pressure. If there is air at the top of the radiator it will get expelled first. Then, as the engine cools it creates a vacuum and will Hoover the fluid out of the overflow tank back into the radiator leaving little or no air in the system.

 

[explorer2030]

I did 4 back to back pressure tests to 18 psi on the system for about 2 minutes each with the overflow tank hose disconnected, and the coolant level was down at the bottom of the filler neck each time I removed the pressure test tool. I added about 1 ounce of coolant to refill the radiator before each retest, so the question is where did the approximately 4 ounces of coolant I added go? There were no external leaks, no visible coolant on the dipstick, and I didn't hydrolock my engine when I started it.

 

[Fabulous50s]

I did 4 back to back pressure tests to 18 psi on the system for about 2 minutes each with the overflow tank hose disconnected, and the coolant level was down at the bottom of the filler neck each time I removed the pressure test tool. I added about 1 ounce of coolant to refill the radiator before each retest, so the question is where did the approximately 4 ounces of coolant I added go? There were no external leaks, no visible coolant on the dipstick, and I didn't hydrolock my engine when I started it.

This is an unpressurized tank for a pressurized radiator? My pentastar uses a pressurized degass bottle with the cap only venting air.

 

[explorer2030]

This is an unpressurized tank for a pressurized radiator? My pentastar uses a pressurized degass bottle with the cap only venting air.

This is a 2015 Jeep which has the cap directly on the radiator, and uses an unpressurized overflow bottle. I pressurized the cooling system at the radiator neck after disconnecting the hose to the overflow bottle.