Thermostat/water pump problem?

[mikeinpa]

While checking under the hood today I noticed my over-flow container for coolant was almost empty. So I filled the container with antifreeze to the "fill to this line when cool" line. After I took it for a lengthy drive (about 50 miles) I checked again and the coolant level looked like it hadent budged. I am not overheating of seeing any leaks but Im wondering...shouldnt the coolant from that container get sucked into the system when the thermostat opens and coolant starts to circulate?

Is this a problem thermostat or water pump?

 

[MrShorty]

When you run the engine, the coolant in the radiator/engine warms up and expands. When it expands enough to overcome the pressure exerted by the "valve" in the radiator cap, it pushes out into the coolant reservoir. So, when the engines warm, it should be above the "full cold" line. Then when the engine/radiator cool down, the excess coolant is sucked back in.
Is the engine warming up?

 

[mikeinpa]

yes...engine warms up and runs fine. It just doesnt seem like there is a change in level in the over-flow...doesnt matter if its cold or hot, the level is staying the same.

 

[Alec]

If there is truly no flow from the overflow tank to the radiator and back, I think that means a bad radiator cap.

 

[mikeinpa]

Alec...are you kidding me?

 

[mikeinpa]

Could it really be something as simple as a radiator cap?

 

[Alec]

If it's just that fluid isn't moving back and forth, yes.

 

[Runnin'OnEmpty]

Alec is right on about the radiator cap. The cap has to seal in two places; against the bottom radiator seat, and against the top radiator flange. If the top isn't sealing, the radiator vacuum will be lost and no coolant will return from the overflow bottle.

I have even bought new radiator caps that would not seal correctly. Sometimes you have to bend the cap tangs slightly to get a good top seal.

 

[Steved]

rad cap

I bought a new cap in Pep Boys the other day but it doesn't fit . I looked at the display and all I saw were different cap rated by lbs. I bought the 16 lb cap but it's the wrong one.

Are they vehicle specific?

 

[Rhett]

Sometimes if you get a new radiator but re-use your old cap, it won't seal properly. This is because the old radiator cap has "set" to the contours of your old radiator due to all of the heating/cooling cycles it's been through.

On the OHV engine it is a 16 lb cap. I know with other vehicles they have different lb pressure caps. 13 lbs seems to be pretty popular with some cars. I wouldn't put a 13lb cap on your Explorer radiator though.