HELP!! - Coolant Overflow filling up and not returning - WTF?

Ive search the entire universe and cant obtain a concrete solution as the answers where all over the place ... lol. :(

Hi guys,

In the last couple of days,

noticed that the coolant overflow bottle is filling up and not returning the coolant back into the radiator. Therefore i am constantly topping up the radiator when it has cooled down.

There is signs of coolant in the top tank when i top up - so the radiator is not dried up.

Seems that its not holding pressure or there is AIR in the system.

Inspections
- No signs of any leaks/worn rad hoses or punctured clamps etc.
- Temp needle fluctuates from middle line to just above the middle line
- Radiator has no signs of any leaks, damaged core/fins, or any signs of oil/gunk residue.
- Water pump is good as gold and no signs of leaks either
- Coolant has not reach boiling point level (coolant not boiling)
- HG not damaged/leaking (afaik)
- Heater hoses are connected correctly
- The siphon on the overflow is good and no signs of holes/punctures etc.
- Overflow bottle/cap is on and not damaged
- Radiator fan turns on but very late - and i would assume its too late when it turns on that the coolant overflowed to the bottle by this point.

Whats been done
- It has a low temp thermostat
- It used to have a low temp fan switch but was replaced back to OEM item due to connector damaged.
- Radiator is an ebay 43mm Alloy high quality core
- Radiator Cap is a 1.1bar (came with the radiator)
- Coolant was flushed recently 40c/60w mix

What could be the problem?
- Should i replace back to a low temp fan switch?
- replace to a new low temp thermostat for assurance?
- Reflush the entire system again for assurance?
- Bleed the system? (how do you bleed the cooling system properly? is there a DIY? - where is the bleed valve on the top hose housing?)
- Replace the crappy 1.1bar rad cap for a 1.3bar cap ftw?
- Radiator fan turns on but very late - and i would assume its too late when it turns on that the coolant overflowed to the bottle by this point.

oh its a B20VTEC conversion recently.

thnx fellaz

By the sounds of it, the radiator cap is faulty. Replace the cap and see how you go

It may also be that the cap you're using is not matched to the radiator. Check the diameter of the washer and whether it is contacting it's seat. You should have to push it down slightly against it's spring before turning.

Quote:

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Originally Posted by hondapop

It may also be that the cap you're using is not matched to the radiator. Check the diameter of the washer and whether it is contacting it's seat. You should have to push it down slightly against it's spring before turning.

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yeh im getting one this weekend, its funny coz when i put the rad cap in it just slips in smoothly without any force .... doesnt seem right ..but yet again ..was working ok when i had my b16 ...

Quote:

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Originally Posted by stndrd

By the sounds of it, the radiator cap is faulty. Replace the cap and see how you go

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getting one on the weekend ... hopefully someone's got one that matches the diameter of my rad ...

Problem is definitely the cap. It's spring loaded to allow coolant flow from the overflow bottle to the radiator. Looks like yours allows flow from the radiator to the bottle but not the other way.

Quote:

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Originally Posted by Banana_hammock

Problem is definitely the cap. It's spring loaded to allow coolant flow from the overflow bottle to the radiator. Looks like yours allows flow from the radiator to the bottle but not the other way.

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I hope so.. Imma change to low temp fan switch anyways and get a rad cap.

Will update shortly

If you are running low temp fan switch, low temp thermostat & high pressure rad cap, you will need to re-tune your ecu so that your afr's are all accurate to the lower engine temp's instead of having it over fuel thinking that it is still in the warm up period

the oem fan switch is fine. never had any dramas with it.
even when pushing the car hard. still stayed cool, temp bar never went any higher. even with a leaking radiator core ;)

Most likely what everyone is saying, the radiator cap.

i Changed to the below;

New Mugen Low temp thermostat
JRacing Low Temp Fan switch
New Greddy 1.3bar Rad cap

and still does it .. doesnt overheat at all, but everytime im done driving and let the engine cool down ...i checked the radiator and the top tank always requires top up as the fluid is in the overflow reservoir...

the radiator is not dried up nor has any leaks ..

might have to get a proper KOYO rad and see if this resolves the problem ..

Try re-bleeding the cooling system with the heater on & then see what happens. You could still possibly have an air pocket

Quote:

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Originally Posted by stndrd

Try re-bleeding the cooling system with the heater on & then see what happens. You could still possibly have an air pocket

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ive bleed it so many times ...even having the fan turn on like 3-5 times on idle with the heater on full blast ..still not fixing the issue.

when i leave the rad cap open, i watch the coolant levels go up and overflows from the top tank (not blubbling) then drops the levels in the top tank as the fan turns on - i then top it up with coolant as the fans go on..

weird shit.

apparently it never had any issues with a full sized radiator tank.

mayb i need to switch to full size?

Have a chat to the boys at BYP as they supplied the engine for you and will be able to advise you accordingly