Fill a radiator with it running. If the bottle is not presurized it does not matter if it it is running or not.
Add Coolant to Warm Engine?
- Thread starter viscous
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I understand the intent to reduce air pockets by filling the radiator while running, but how about filling the radiator while off, then run engine a bit, then check radiator again after it cools?
Makes sense.
Alright, I plan to properly fill the radiator, overflow bottle, and make sure the system is bled. I hope nothing goes wrong with the radiator cap when I remove it...hasn't been removed in a while.
You're making this way too complicated.
Sounds like you have a dry overflow tank and the radiator is either full or very close to full.
Add enough coolant mix until the tank is at max. Recheck in a few days and add more if needed.
Sounds like you have a dry overflow tank and the radiator is either full or very close to full.
Add enough coolant mix until the tank is at max. Recheck in a few days and add more if needed.
Yea, that's what I was just about to say. Could the system have some air in it? Maybe, but it wouldn't be enough to make much of a difference. I still didn't see anywhere what car this was. Some cars are pickier than others, but generally, just put the fluid in the overflow and be done with it.
+1 Knowing what car it is would have been very helpful. I mentioned that early on, and we still don't know. If it's anything like my old Ford the OP has nothing to worry about, my Wrangler, that's another story.
As far as the hose between rad and overflow tank, any air that's in it will burp out when the engine warms up and the rad sends coolant. So it's fine to fill the overflow tank anytime-- warm or cold. You can even fill it a little beyond the marks-- the worst penalty is a little coolant will find its way out if it gets hot. Similarly, it siphons back when cold, but takes a little vacuum to form a siphon, so you should always find a little air pocket when you open the rad cap on a cold motor.
Since the radiator cap keeps pressure on coolant, keeping it from boiling, it might come out the hose as coolant vapor, since it's now not under pressure. Having adequate (or above-adequate) coolant in the overflow tank gives these bubbles of vapor more time to cool back down, condensing into liquid, which saves you from slowly losing it to boil-off.
To be clear to all in this thread, I am assuming a non-pressurized overflow tank vs a pressurized "surge" tank. The difference is the surge tank will have a better-sealing cap. Overflow tanks have a flimsy one not unlike the windshield washer fluid one.
Since the radiator cap keeps pressure on coolant, keeping it from boiling, it might come out the hose as coolant vapor, since it's now not under pressure. Having adequate (or above-adequate) coolant in the overflow tank gives these bubbles of vapor more time to cool back down, condensing into liquid, which saves you from slowly losing it to boil-off.
To be clear to all in this thread, I am assuming a non-pressurized overflow tank vs a pressurized "surge" tank. The difference is the surge tank will have a better-sealing cap. Overflow tanks have a flimsy one not unlike the windshield washer fluid one.
That would be a bit easier. Perhaps I'll start by doing this. Do old radiator pressure caps develop problems such that when eventually removed, they can cease functioning properly when reinstalled?
Good, I'll just fill it cold, then.
That's right, just a non-pressurized overflow bottle, as I indicated.
Never heard of that issue. Inspect the cap when it is off, replace if needed.
That's good. Wouldn't want to have to buy a new cap just because I removed it and disturbed something. Anyway, I think I'll just fill the overflow tank to start. Perhaps check radiator and bleed system later.
If you have a cap that starts malfunctioning when you reinstall it, it wasn't long for this world in the first place. Better to catch it now before it leaves you walking somewhere with an overheated car, or worse.
JHZR2
Staff member
Im kind of confused with this. You dont know actual level of coolant in the radiator?
Why wouldnt you have the coolant in the reservoir at the appropriate level to begin with? IME, theres always a min/max level that is on the reservoir. Having the coolant at that level to begin with would resolve some issues...
Why wouldnt you have the coolant in the reservoir at the appropriate level to begin with? IME, theres always a min/max level that is on the reservoir. Having the coolant at that level to begin with would resolve some issues...
Correct. I haven't removed the pressure cap. I was concerned that it might not seal properly after having been removed. It hasn't been removed in a while. I'm also reluctant to open the system bleeder valve for fear of not being able to seal it up properly.
"to begin with"? As in, before checking the level in the radiator? Yes, that's the tentative plan. As others have mentioned, having the correct level in the overflow bottle doesn't guarantee an air-free system. Are you suggesting that filling the overflow bottle alone should resolve the problem, without opening the pressure cap?
JHZR2
Staff member
Unless you live far in the boonies and can’t get a new cap for weeks, I still don’t quite get the concern about the cap.
Im pretty sure that the cap on my Ram is original at 438k and 26 years, and if the caps on my MB cars aren’t original, they still have a pretty good fraction of 40 years on them...
I have my doubts that a cap gasket would tear, so I think the risk of damage is fairly low.
As far as the overflow, my interpretation is that you’re currently observing a dry bottle that gets some fluid in it as the system heats up. I’m lacking an understanding of why you wouldn’t be proactive about it, and since it’s the summer, at least fill between min and max levels with distilled water or ideally, some 50/50 mix. I agree that it doesn’t guarantee a full radiator, though it ought to be close... but it does get you out of a do loop where there’s a chance of air being sucked back as the system cools. Keeping the reservoir at the right level,would at least create a liquid seal... nothing more, nothing less.
I'm trying to address this the best way possible, so I asked here for help.
JHZR2
Staff member
No problem with asking for help. Point was intended to be, why wouldnt you at least add water in the reservoir to the min point before doing anything else, regardless of path forward? Then your system is running the chance of sucking in air... Then from there you can proactively prepare to check things out and move forward....
