Add Coolant to Warm Engine?

[viscous]

When engine is cold, overflow bottle is dry. As engine warms, some coolant enters the (non-pressurized) overflow bottle through bottom orifice. Not much coolant in there, even at operating temp. This coolant makes the bottle bottom feel quite warm, but not very hot.

Planning to add 50/50 coolant and distilled water to overflow bottle, but thought it best to do so while there's already some coolant in there, so as to avoid an air gap in the overflow bottle hose. Intend to run engine until coolant enters overflow bottle, then shut off engine and add coolant before overflow bottle empties. Concerned that room-temp coolant could cause problems as it gets drawn into the warm (albeit cooling) engine.

Which option is best?
1. Fill overflow bottle with engine off but warm, while there's still some warm coolant at the bottom of the bottle.
2. Fill overflow bottle when engine is cold and overflow bottle is dry.

Also, any advantage to adding the coolant while the engine is running? (Would rather not, if possible.)

 

[demarpaint]

Sounds to me like if the overflow bottle is dry then there is air in the radiator and/or cooling system as well. Either way I would make sure it is filled to the cold level on the overflow bottle, when cold, and that the cooling system is properly bled. I'd also check for leaks just to play it safe.

 

[928]

Check the rad cold, fill as necessary then fill the coolant bottle to the line. If you have to add later- find the problem

 

[viscous]

Sounds to me like if the overflow bottle is dry then there is air in the radiator and/or cooling system as well.

Is that necessarily so? Even though coolant enters the overflow bottle as the engine warms?

I would make sure it is filled to the cold level on the overflow bottle, when cold, and that the cooling system is properly bled.

If I fill the overflow bottle when cold and empty, I thought I might trap air in the hose that leads to it. Will this air just bubble out into the bottle as the engine warms?

Check the rad cold, fill as necessary then fill the coolant bottle to the line.

Was hoping to avoid removing the radiator cap. Would my option "1" not ensure a full radiator?

 

[demarpaint]

Is that necessarily so? Even though coolant enters the overflow bottle as the engine warms?


If I fill the overflow bottle when cold and empty, I thought I might trap air in the hose that leads to it. Will this air just bubble out into the bottle as the engine warms?


Was hoping to avoid removing the radiator cap. Would my option "1" not ensure a full radiator?

Once the overflow bottle runs dry air "can" enter the cooling system depending on how low the level of coolant is in the radiator. In this case we don't know that, nor do we know the vehicle in question. Some are worse than others. Depending on the design of the cooling system air can get trapped in the heads, or heater core ,etc and remain there, which is why it is best to top it off and make sure it is properly bled. Coolant is constantly circulating through the cooling system, especially when the thermostat is fully open. If there is air mixed in, pockets of air is circulating too. There are some vehicles that can be a real PITA to bleed, and bleeding is crucial to proper cooling system operation. If it were mine as much of a PITA as it might be I would want to be sure that. A. It had no leaks, and B. it was properly bled.

I recall hearing complaints of Jeep Wranglers making gurgling sounds inside the cabin and complaints of poor heat during the winter. Many of these people had topped up their recovery tanks and went on their way. It was later discovered they had air in the cooling system which was causing the problem. Other vehicles had overheating problems, and/or hot spots in the heads from trapped air. Take an old vehicle like my 88 Ford and it will bleed itself, eventually, and some vehicles won't. Opinions vary on this topic............

 

[viscous]

Once the overflow bottle runs dry air "can" enter the cooling system depending on how low the level of coolant is in the radiator. ... If it were mine as much of a PITA as it might be I would want to be sure that. A. It had no leaks, and B. it was properly bled.

Good advice... thank you. Regarding the initial top-off, does it matter if it's done while the overflow bottle is cold and dry versus warm containing some coolant?

 

[demarpaint]

Good advice... thank you. Regarding the initial top-off, does it matter if it's done while the overflow bottle is cold and dry versus warm containing some coolant?

I like to deal with topping up a cold cooling system.

 

[viscous]

I like to deal with topping up a cold cooling system.

Yes, me too, in particular because I was concerned that the "cold" coolant could warp/crack something as it was drawn into the warmer engine. Is this a potential concern? However, it also seemed potentially advantageous to add the coolant when there was already a bit of warm coolant in the overflow bottle, to avoid creating an air gap in the hose leading to the overflow bottle.

 

[Astro14]

1. You’re not adding enough cold coolant to a warm radiator to worry about thermal shock.
2. Just because there is coolant in the reservoir, doesn’t mean all the air is purged.
3. Any air in the line will be purged as coolant flows back and forth during expansion.
4. why don’t you open the pressure cap and see where the coolant level sits right now, instead of guessing?

 

[demarpaint]

Yes, me too, in particular because I was concerned that the "cold" coolant could warp/crack something as it was drawn into the warmer engine. Is this a potential concern? However, it also seemed potentially advantageous to add the coolant when there was already a bit of warm coolant in the overflow bottle, to avoid creating an air gap in the hose leading to the overflow bottle.

I'm concerned with burns. Adding a small amount of cold coolant into a recovery tank is going to be an issue. With regard to air, there lies your problem. If the coolant is already low in the radiator itself, odds are there is air already in the system. Whether or not it comes out when adding coolant for the top up is the whole point of this discussion, some designs are more forgiving than others. In a modern cooling system I'd be concerned. In my 88 Ford odds are the air will find its way out. My 2016 Rubicon, I have my doubts.......Pop the radiator cap and have a peek, on a cold engine for safety.

 

[viscous]

Any air in the line will be purged as coolant flows back and forth during expansion.

OK, then it sounds like there is no advantage to my initial plan of topping off when the overflow bottle already contains some warm coolant (even if there's no risk of thermal shock in that plan). I might as well just top off when the bottle is cold and dry.

why don’t you open the pressure cap and see where the coolant level sits right now, instead of guessing?

Pop the radiator cap and have a peek, on a cold engine for safety.

Opening the radiator cap seems to be the common recommendation, which seems reasonable. I had hoped to avoid this, so as to avoid inadvertently creating a new problem, but if it's the only way...

 

[wpod]

Radiator cap? replace it then check for leaks.

 

[JohnnyG]

Most overflow tanks also have a small "air bleeder" line which is supposed to constantly allow a small stream of coolant to circulate through the tank then back into the engine block. These typically come out of the engine at a high point which serves to eliminate any air in the block. These will sometimes get plugged after MANY miles of service. If you have one, make sure it is flowing.
If it's plugged, don't simply blow the line back, which will put anything blocking the line back to where it might plug it again. The hose and fittings should be removed and inspected in order to remove any debris, then reinstalled.

 

[pbm]

Quote from OP: "Planning to add 50/50 coolant and distilled water to overflow bottle,"

Wouldn't it be better to add 'concentrate' and distilled water...or...50/50 alone?

 

[JohnnyG]

yes. Just the 50/50 coolant, unless he's trying to lower the concentration for some reason. No location given.

 

[viscous]

Radiator cap? replace it then check for leaks.

The pressure cap. Replace it with a new one, you mean?

Most overflow tanks also have a small "air bleeder" line [that] will sometimes get plugged after MANY miles of service. If you have one, make sure it is flowing.

Good suggestion. Thanks.

Wouldn't it be better to add 'concentrate' and distilled water...or...50/50 alone?

yes. Just the 50/50 coolant, unless he's trying to lower the concentration for some reason.

I stated that in a convoluted fashion. When I said "add 50/50 coolant and distilled water" I meant "add a 50/50 mixture of coolant [concentrate] and distilled water"

 

[Chris142]

Start the engine cold. Remove cap and fill bottle to safe zone with engine running. Put cap back on. Let it fully warm up. Shut it off. Recheck after it has cooled.

 

[viscous]

Start the engine cold. Remove cap and fill bottle to safe zone with engine running. Put cap back on. Let it fully warm up. Shut it off. Recheck after it has cooled.

Why while running?

 

[Chris142]

Why while running?

That way it is circulating with no air pockets. Most manufacturrers recommend it running

 

[viscous]

Why while running?

That way it is circulating with no air pockets. Most manufacturrers recommend it running

Very well, then. Thanks. To be clear, are you suggesting, as others have, that I remove the radiator pressure cap to check the level in the radiator? Or did "remove the cap" simply refer to the overflow bottle cap?