You probably didn't get the cooling system full. You didn't say what engine your car has. My Hemi cooling system takes some doing to get it full after replacing the thermostat. You are supposed to remove the vent plug in the water pump close to the thermostat and vent all of the air. I couldn't get that plug out so I just used a large funnel on an extension so the level in the funnel was much higher than any point in the system and the air slowly burped itself out of the system.

a funnel such as this

https://www.lislecorp.com/specialty-tools/spill-free-funnel-606

 

This is the correct procedure IF you can't get the bleed plug out. The stupid factory torque that plug down way more than it needs to be. I've been fortunate on my Hemi's and have been able to get them all out without issue. When reinstalling I either use a little teflon tape or some non-hardening Permatex No. 2 sealant and torque them ONLY enough so they don't leak and then slightly more.

2005rtmag is correct, you probably haven't gotten all the air out of the system. On mine, using the bleed plugs, I fill them until coolant just begins to come out (put some rags below so you don't get coolant on the accessory drive belt or you'll have other problems) and then install the plug. Continue the fill in the overflow tank until it is at the "Cold Full Max" level. Drive it for a day or so and then again, when the engine is cold, check and fill to the cold level again. Be sure to cycle the heater a few times too. Sometimes it'll take 4-5 days of doing this to get the coolant level spot on and you won't have to add any more coolant. It should never overheat during this time, if done correctly, even though there is still small amounts of air in the system.

When you installed the new thermostat, did you install it with the small "jiggle" bleed valve in the up (top) position? If not, it'll just take longer to get all the air out, but once it is all out there shouldn't be any problems.

 

From the manual

COOLING SYSTEM FILLING
WARNING: Make sure engine cooling system is cool before removing pressure cap or any hose. severe
personal injury may result from escaping hot coolant. The cooling system is pressurized when hot.
Note: Cooling system fill procedure is critical to overall cooling system performance.
1. Close radiator draincock. Hand tighten only.
2. Install engine block drain plugs, if removed. Coat the threads with MoparT Thread Sealant with Teflon.
WARNING: When installing drain hose to air bleed valve, route hose away from accessory drive belts,
accessory drive pulleys, and electric cooling fan motors.
Note: It may be necessary to install a bleed fitting on the 5.7L engine.
3. Attach a 1.5 - 2 m (4 - 6 ft.) long 6.35 mm (1/4 inch.) ID clear hose to bleeder fitting
² Bleed Valve Location (2.7L): Located on the water outlet connector at the front of engine.
² Bleed Valve Location (3.5L): Located on the lower intake manifold, left of center and below the upper intake
plenum.
² Plug Location (5.7L): Located on the front of the water outlet housing at the front of engine.
4. Route hose away from the accessory drive belt, drive pulleys and electric cooling fan. Place the other end of
hose into a clean container. The hose will prevent coolant from contacting the accessory drive belt when bleeding
the system during the refilling operation.
Note: It is imperative that the cooling system air bleed valve be opened before any coolant is added to the
cooling system. Failure to open the bleed valve first will result in an incomplete fill of the system.
5. 5.7L ENGINE - Install a threaded and barbed fitting into water pump housing.
6. Attach Tool 8195 (1), Filling Aid Funnel to pressure bottle filler neck.
7. Using hose pinch-off pliers, pinch overflow hose (3) that connects between the two chambers of the coolant
bottle (2).
8. Open bleed fitting.
CAUTION: Do not mix coolants. If coolant is used other than specified, a reduction in corrosion protection
will occur.
7 - 14 COOLING LX
9. Pour a 50/50 mix of MoparT Antifreeze/Coolant, 5 Year/100,000 Mile Formula and distilled water into the larger
section of Filling Aid Funnel (the smaller section of funnel is to allow air to escape). For system capacity, (Refer
to 7 - COOLING - SPECIFICATIONS).
10. Slowly fill the cooling system until a steady stream of coolant flows from the hose attached to the bleed valve.
11. Close the bleed valve and continue filling system to the top of the Tool 8195 (1).
12. Remove pinch-off pliers from overflow hose.
13. Allow the coolant in Filling Funnel to drain into overflow chamber of the pressure bottle.
14. Remove Tool 8195 (1). Install cap on coolant pressure bottle.
15. Remove hose from bleed valve.
16. 5.7L ENGINE - Install fitting into thermostat housing. Coat the threads with MoparT Thread Sealant with Teflon.
17. Start engine and run at 1500 - 2000 RPM for 30 minutes.
Note: The engine cooling system will push any remaining air into the coolant bottle within about an hour of
normal driving. As a result, a drop in coolant level in the pressure bottle may occur. If the engine cooling
system overheats and pushes coolant into the overflow side of the coolant bottle, this coolant will be
sucked back into the cooling system ONLY IF THE PRESSURE CAP IS LEFT ON THE BOTTLE. Removing
the pressure cap breaks the vacuum path between the two bottle sections and the coolant will not return to
cooling system.
18. Shut off engine allow it to cool down for 30 minutes. This permits coolant to be drawn into the pressure chamber.
19. With engine COLD, observe coolant level in pressure chamber. Coolant level should be within MIN and MAX
marks. Adjust coolant level as necessary.
Note: The coolant bottle has two chambers. Coolant will normally only be in the inboard of the two. The
outboard chamber is only to recover coolant in the event of an overheat or after a recent service fill.
ADDING ADDITIONAL COOLANT
The use of aluminum cylinder blocks, cylinder heads and water pumps requires special corrosion protection. Only
MoparT Antifreeze/Coolant, 5 Year/100,000 Mile Formula (glycol base coolant with corrosion inhibitors called HOAT,
for Hybrid Organic Additive Technology) is recommended. This coolant offers the best engine cooling without corrosion
when mixed with 50% distilled water to obtain to obtain a freeze point of -37°C (-35°F). If it loses color or
becomes contaminated, drain, flush, and replace with fresh properly mixed coolant solution.
CAUTION: Do not use coolant additives that are claimed to improve engine cooling.

 

Did you put on a new pressure cap?

 

Santa Tom LaBelle. Yes I replaced the pressure cap. Also purchased the Lisle funnel kit to help me bleed the cooling system.

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Chances are there are still a few pockets of air in the system and the level in the reservoir tank will go down a bit. On mine, I usually have to top off the reservoir a few times within a week to get it to where it stays where it should.

 

Magnuman should I still use the Lisle funnel kit to keep topping it off?. I was going to check the level everyday to see if it goes down any. So assuming it doesn't go down any this week. Am I'm safe to assume all the air is out?

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No, you won't need the funnel now. When the engine is cold, just fill the reservoir to the "Max Cold Fill" level mark and drive it normally. When the level stays there when cold you should be fine.

As a side note, none of my 3 Chrysler vehicles (all Hemi's) will stay at exactly the "Max Cold Fill" level when cold. They all seem to maintain a cold full level at about 1 1/4 in. above "Low" level. I have them all marked where they like the levels to be. If I fill to the "Max Cold Fill" level, they'll all seek the lower level after a little time. If yours tends to do that too, I wouldn't worry about it.....just be sure it maintains its cold level every time you check it. If it goes below that level, you probably have a slight leak somewhere. All of mine stay at the marked level.....always. If it were to go below that, I'd know something was up and I would then do a pressure check of the entire system and the radiator cap.

 

Thanks magnuman. Checked this morning. It's still over the max fill line. I guess I'll pump out some of the antifreeze our since I over filled the reservoir tank

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Yep, that's fine. Mine all run only about an inch or so above the add line and they've been that way for years.....except my 300CSRT8 which I just bought in January.

 

Thanks magnuman. I will keep a eye on as the weeks go on. I will post any updates to these same post. Thank you all for helping me out.

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