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Coolant questions

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Wrathvr4

Proven Member
47
11
Sep 15, 2021
Brisbane, California
Chasing down answers to what could be something small or possibly a HG job. Been reading for days on this topic but can’t find anything on here that fits my symptoms.

No matter how much coolant I poor in to my radiator I cannot get it to settle at the top of filler neck, coolant 30mm below the overflow outlet. It always sits below filler neck, and requires a small bit of top up every time.

I’m pushing coolant, but it seems to be returning back to radiator when engine cools but not Enough to fill up the filler neck. Can I still have a bad HG even if overflow vac still returns coolant to rad?

As far as I am aware, coolant should always sit full in the filler neck.

I have a civic 3 core half rad. Everything seems to be working the way it should. No overheating.

Any help on this topic would be much appreciated.
 
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Are you actually losing coolant or it's just not returning to the level that you want it to?

In my truck I run two inches below the upper tank top, any higher and it blows out the overflow and settles itself back to where it wants to be. Every design is different though. I have no experience with civic radiators, I run a golf mk3 radiator but that may just be how that radiator likes to run.

If you are actually losing it, you can check your plugs. They can get a greenish tint to them when burning antifreeze but if you're not burning that much it may not show. Can also check your oil
 
For what it's worth my coolant level disappears from the filler neck area after one drive. I would assume it is just settling where it wants to be. If you have a nicely sealed coolant overflow system and your cap is good, it will level itself. If you want to ensure you aren't losing any, top it off and let it heat cycle once. Then top it back off taking note of how much it takes to bring it back to the neck area. Then drive it a few times and top it off again. Did it take a bunch more than the first time? Might be time to investigate further. Did it take basically the same? No cause for concern.
 
As I think you know (but just to cover bases for others who may read this) - if the system is in perfect condition the increased pressure when the system is hot will push excess coolant into the overflow tank. When the system cools and the fluid contracts the system goes into a vacuum and sucks coolant back out of the overflow tank and into the radiator. So ideally the cooling system will always be full to the top of the radiator cap.

Absent any coolant loss/air ingest due to leaks (head gasket, turbo, hose, crack in the radiator, etc.), my guess for the extra air in the system would be due to either a bad radiator cap (large gasket that seals the cap against the radiator neck is warped, cracked, or split) or there is a crack or gap in the overflow hose that is allowing air to get in when the system is under vacuum (like a split drinking straw).

This little bit of excess air won't hurt anything, assuming your car isn't abnormally demanding of the cooling system (abnormally high engine temps due to high boost, nitrous, etc.). The air will reduce the cooling capacity a little bit as it compresses, but this will be minor at best. Biggest thing will be to ensure there aren't any leaks that will cause things to get worse and that the air isn't circulating in the system. If the air circulates it can and will gradually collect in the high spots in the head where it will super heat and create hot spots that will eventually lead to significant problems.
 
I think I’ll run a few more heat cycles and see how she acts. My concern is I have pushed coolant, however it wasn’t bubbling or overheating and obviously the low coolant levels below the neck. Might just need to work more air out of the system. Will report back in a couple days.
 
yes, the radiator coolant should be right up to the cap. In most cases the radiator should be full enough that some coolant will spill when you open the radiator cap. First make sure the hose to your overflow tank fits tightly, if loose it will draw air. There should be a dip tube so the overflow hose draws from the bottom of the overflow tank.

Secondly, check everywhere for leaks. Let sit with a pressure tester for hours if needed. Some slow leaks won’t hit the ground, just evaporate off the engine. Let your nose be your guide. Coolant has a distinct smell. If you smell coolant after a good drive you have a leak somewhere. You have to find it, and it could be a lot of hard to see places. If you have a leak it may be drawing in air from the leak point rather than pulling coolant back from the overflow or you may just be losing the coolant causing your low level.
 
@Wrathvr4 What did you find out?
Nah man, still haven’t solved it. Since I last posted on here I have pressure tested the coolant system which held 18psi for 24 hours, I flushed the whole system including heater core, I ran a compression test and leak down which returned excellent numbers all around. I am stumped

I’m wondering if running a 3 core half rad and aftermarket overflow tank has anything to do with it?

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No matter how much coolant I poor in to my radiator I cannot get it to settle at the top of filler neck, coolant 30mm below the overflow outlet. It always sits below filler neck, and requires a small bit of top up every time.

When the level is 30mm down, how deep is the coolant over the tops of the tubes? 20mm maybe?
What happens if you don't top it up? Will the level keep going down, 40, 50mm down, until the tops of the tubes aren't even under water anymore?
 
Which model of Proflow do you have?
Is the top of it vented freely to atmosphere, or is it the type that becomes pressurized?

The one on my car is the type that is freely vented to atmosphere and I like it. With that type you have to be able to see how full it gets when hot, and how empty it gets when cold. Because if it gets too full when hot, it will push some coolant out the dump tube. And if it gets too close to empty when cold it will suck some air in during the last bit of cool down.
That's why the vented types are usually made of translucent plastic, so you can see inside without touching it.
 
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Thanks for all the responses, I changed out the radiator after testing everything else and looks to have solved the issue. Mishimoto in my opinion is no good
 
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