Thermostat doesn't control coolant going back an forth between the radiator and overflow. Did you by chance change the radiator cap? If you're radiator is really empty, then you have something more going on. The overflow will only hold a fraction of the radiator capacity. Any other changes recently besides the water pump?

 

Have you checked your dipstick to see if there is water in your oil?
You could pressure check your radiator.

 

No water in the oil. Now that I am looking more, I do see coolant residue on the side of the radiator right beneath the cap and also a little on the top of the battery. Looks like it might be pushing out of the cap? Rookie question, The radiator I have has the "be cool" cap that came with it. Can I just replace that with a generic radiator cap from autozone? Then I assume, add back coolant and let it run?

Should I also remove some of the extra fluid in the reservoir as well?

 

Sounds like you're burning off your antifreeze........

The rad cap lifts from pressure and allows expanded coolant into the overflow.
The cap also has a vacuum actuated valve for when the coolant shrinks as it cools in the rad. At this point it sucks back into the rad.

 

A defective or the wrong type of radiator cap will not allow the coolant in the overflow (expansion) tank to return to the radiator.
Also you say the "radiator is empty but the overflow tank is full with no visible leaks" but your radiator will hold 2 gallons or more while the overflow will only hold about 1/2 gallon or so,depending on its size.
SO either the radiator isn't totally empty OR you have lost a lot of coolant without really seeing it (this I doubt happened) OR its mixed in with oil as Brad has mentioned
More than likely the level was further down in the rad than could be seen without a flashlight. First thing is make sure your rad cap is designed for an overflow tank, many older caps would just let the overflow hit the ground and the coolant level was left down about 2" to allow for coolant expansion.
If replacing the rad cap has no effect than its time for a pressure tester to be rented at the parts store.

 

You do know that one is not supposed to fill the radiator all the way to the top. The correct (full) level is approx 3-4 inches below the top. If one fills it tothe top it will overflow every time.

 

Not true if he has an overflow tank. On my car the radiator is always full to the top. As the coolant expands it flows into the overflow tank and as it cools it sucks back into the radiator. I use a Stant cap for overflow with the small metal disc on the bottom of the rubber that seals to the radiator neck.

 

Can I just replace that with a generic radiator cap from autozone? Then I assume, add back coolant and let it run?

Should I also remove some of the extra fluid in the reservoir as well?

Yes on replacing the the radiator cap with one designed for an overflow tank. I would remove coolant from the overflow - probably shouldn't be more than 1/4 or 1/2 full.
Per Brad's comment above, I probably keep my radiator too full, but it regularly moves coolant back and forth between the radiator and overflow as it expands/contracts. I used a sharpie to mark the overflow tank level when cool and when hot so I can monitor.

 

Thanks. I am going to drain the over flow, get a new radiator cap and put in new fluid and see what happens.

After looking with a flashlight, the radiator is not completely empty. Probably an 1/8- 1-4 filled. So I think some fluid went to the reservoir and some spilled out from the cap.

We will see if that works.

How do you know if the cap is designed for an overflow tank?

 

If you have a coolant reservoir, you can fill the radiator to the top, the reservoir about half full is correct. This would be a closed system, make sure the overflow hose it tight at the radiator!

 

Make sure the coolant tank is plumbed so that coolant can travel back into the radiator. Some are strictly catch cans.

 

Make sure the coolant tan is plumbed so that coolant can travel back into the radiator. Some are strictly catch cans.

Exactly right - in my case, the overflow tube is connected to the base of the overflow tank. I believe others feed through the top, but have a stem that reaches to the bottom of the tank. The key being it can't allow air to be sucked back which defeats the purpose.

 

To each his own. Some years ago I ran an overflow bottle on my 69. After running it for several years and not a single drop ever going into the overflow bottle I removed it. All I did was run my radiator at the correct level. My car runs consistently between 190-200 degrees. So I see no advantage to running my car with the radiator full and then needing an overflow bottle.
In addition if when ones engine reaches operating temperature your cooling system spits out fluid into an overflow container then your system is operating with lesser volume of coolant anyway. That coolant that is sitting in your overflow container is not assisting in cooling your engine.

 

Guys, tuck it in and help the OP with his issue, you can easily start a new thread and hash this out.

@mangrum1126 leave the cap off, fire the car up, can you see bubbles or smell exhaust coming from the radiator?

 

Let me get some time this weekend and I will let you know.

 

Is it possibly leak into your interior from your heater core?

 

No heat or AC in car.

 

Have you been driving the car or at least running the engine? If so have you noticed any white exhaust smoke?

 

No white smoke. I am thinking two issues currently. 1) bad cap and 2) too much coolant.

I am going to drain, refill, Bleed the system, and add a new cap and then report back.

 

Problem resolved. I believe it was a bad radiator cap.

I drained the reservoir tank, replaced the radiator cap, then filled the radiator up and bled the system. Let the car run for 30 minutes with a coolant filling funnel to get the air out. Then later in the evening, let it run another 30 with the new cap on. Car would get up to about 190 before the fans kicked on, then drop down to 180 and hold. No spillage from the cap and actually no fluid came into the reservoir. I am assuming with the thermostat and the dual fans, the coolant never gets hot enough to boil out to the reservoir. The cap is 13psi, so I would assume it would not let overflow until like 250 degrees.

Thanks for the help and suggestions.

 

Yes!

 

You need to fill the overflow jug about half full.
Then it will take what it needs.

 

If you still find out you have the problem look for exhaust leaking into the cooling system and forcing the fluid to the reservoir tank. Head gasket.

 

Make sure the fluid level in the tank is higher than the fluid level in the rad depending on type.

Setting up Your Cooling System - Expansion vs Recovery Tanks

A coolant recovery tank has the ability to discharge and recharge coolant. An expansion tank is pressurized and holds a pocket of air for expansion.

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