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Old 05-26-2019, 10:21 PM   #1
wpavlis
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Coolant level question

First off, thanks to everyone who has answered my many questions in the past. I fired up the new 350 that i just installed in my 68 c10 today. During break in as the motor came up to temp the radiator puked a bunch of water. Temperature was fine bit i checked and from what i could tell everything was fine. Finished the break in and temp held rather steady the whole time. When it cooled down i checked the coolant in the radiator and it was an inch or two low. I filled it back up and took a quick test drive around the block and it puked some more coolant again.

Now to my question. Is this normal on an open system? I have never owned a vehicle without a coolant bottle. I am guessing this is just the system equalizing and if i had a coolant catch bottle it would get sucked back in as the radiator cooled back down. Does that sound correct? Thanks again for all the help and advice.
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Old 05-26-2019, 10:26 PM   #2
truckster
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Re: Coolant level question

In an open system there's usually about an inch between the top of the radiator and the coolant level. There has to be room for expansion.
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Old 05-27-2019, 01:01 AM   #3
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Re: Coolant level question

That is what i figured. Thanks for confirming!
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Old 06-02-2019, 09:27 PM   #4
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Re: Coolant level question

You probably had an air pocket that cleared out.
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Old 06-02-2019, 11:44 PM   #5
wpavlis
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Re: Coolant level question

I have a quick follow up story. When this happened i was using straight distilled water. I did this just in case i had some kind of leak during the break in period. I figured that if i did have a leak it would be less mess if i was only using water. The plan was to drain some water out and replace it with coolant. What i didn't think about was the fact that the coolant raises the boiling point significantly. After draining out the water and refilling with coolant to get a proper mix, the level has stayed much closer to what i would expect. It also seemed to puke less coolant when fully warmed up. I think the combination of only using water and not ever having owned a car with an open system caused me to get overly worried.
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Old 06-03-2019, 09:38 PM   #6
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Re: Coolant level question

You could have the wrong radiator cap on there. If it is a closed system the cap needs to be for that system.

A open system cap of course would allow coolant to escape out!
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Old 06-04-2019, 02:52 PM   #7
wpavlis
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Re: Coolant level question

I believe all radiator caps will allow coolant to escape when the system reaches the rated pressure correct? The difference is that the cap for a closed system allows coolant to be pulled back in from the overflow bottle. Without an overflow bottle it just lets air in rather than maintaining a vacuum. That is how i understand it anyway. Please correct me if i am wrong.
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Old 06-04-2019, 02:56 PM   #8
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Re: Coolant level question

Also, to be clear my radiator only vents coolant once. If i fill it all the way to the top it will let a little coolant out when it heats up (i assume due to expansion) . Then it will not do it the next time. I think i just got overexcited it being the first time i ever swapped a motor.
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Old 06-04-2019, 03:48 PM   #9
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Re: Coolant level question

sounds like everything is ok to me.. from what I'm reading anyway..

you are correct about the pressure caps.. an open or vented system does not need the vacuum seal in the cap to draw coolant back into the system obviously because it doesn't have a reservoir to draw it from

so the principle difference is, in a closed or reservoir system, the vacuum seal in the pressure cap will open when the engine is off and coolant temperature is lowering which creates a vacuum.. this keeps the system completely full or flooded for optimal heat rejection and also gives the operator a visual indicator of coolant level, as long as the system is tight, by observing the overflow bottle.. also more friendly to the environment

please note, this is not the same as an expansion tank system where the reservoir is pressurized..

in an open system, the pressure cap only has the pressure seal.. this system will operate with an air gap along the top of the top tank which is normal.. this is easily established by filling the system level full, bringing the engine up to temperature and allowing the excess to purge from the overflow bib, hopefully into a hose pointed into a pan..

this process is however a normal product of actual fluid pressure developed by expanding coolant, not overheating, boiling over, etc. once the engine is off again and the coolant temperature decreases, the vacuum may remain in a tight system, slightly collapse larger hoses, etc.. you may recall at some point in your experiences, removing a radiator cap from an older model vehicle and it slurps in a little air.. this is normal and indicates a tight system.. you may also recall the coolant level is approx. an inch from the top, also normal.. when it's at operating temperature, the coolant expansion will nearly or completely fill the system again..

little rule of thumb for y'all, 1 inch of vacuum equals about 2 psi of sealing integrity..

if a closed system vacuum seal pressure cap is used in an open system, the only result is the atmosphere will replace the contracting coolant as it returns to ambient temperature..

so for your situation, you may have to drive it a few times reaching normal operating temp before it settles.. it may purge a few dribbles here and there when at it's highest temps, but eventually it will level off..

if you're conscientious of the actual level, when it's cool or ambient temp, for instance after sitting overnight, take a popsicle stick or similar and dip the tank at the pressure cap and make a reference mark.. if repeated checks under same conditions are consistent, call it done and mark it for duty..

hope that helps, good luck!
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Old 06-14-2019, 12:10 PM   #10
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Re: Coolant level question

On my break in, it seemed to cool fine when the RPMs were up. When I slowed to idle it started puking. I was running without a fan at that time. I was wondering at that time if I'd overfilled it. I was even thinking about installing a puke can.

When I installed the fan it cooled quite a bit better at idle.

When I also installed a fan shroud it cooled perfectly.

Now it's about an inch or two from the top and no more puking.

I might not need a puke can after all.
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