cooling system overflow bottles

cooling system overflow bottles

Author
Discussion

bordseye

Original Poster:

2,044 posts

199 months

Friday 20th January 2023
quotequote all
Header tank with normal radiator cap - the old metal type. Plastic pipe venting surplus coolant to the ground. But I want to put a catch tank on the plastic pipe so that as the engine cools, its sucks back the water that has overflowed. The installation is in my boat and if the water isnt sucked back then part of the heat exchanger is not covered by coolant and the engine overheats under heavy load.

Question is, with a normal cap and overflow set up, will the engine suck back the coolant from the bottle or will it such air from the atmosphere. Does the cap let coolant return?

E-bmw

9,978 posts

159 months

Friday 20th January 2023
quotequote all
Normally the cap works as a pressure relief valve, and that is how is dumps any excess.

As such when not relieving extra pressure it is a closed valve.

Best way may well be to find a newer version of the engine in a newer car that has a more common (these days) expansion bottle set up & replace the rad also.

Obviously is will either need the same hose set up or you will need to adapt them to fit.

Perhaps if we knew the engine it would help with options.

QJumper

2,709 posts

33 months

Friday 20th January 2023
quotequote all
E-bmw said:
Normally the cap works as a pressure relief valve, and that is how is dumps any excess.

As such when not relieving extra pressure it is a closed valve.

Best way may well be to find a newer version of the engine in a newer car that has a more common (these days) expansion bottle set up & replace the rad also.

Obviously is will either need the same hose set up or you will need to adapt them to fit.

Perhaps if we knew the engine it would help with options.
It's in a boat.

OP, might be easier to ask on a boating forum, especially one specific to your make/model as I imagine that kind of thing's been done before if it's causing you problems.

SturdyHSV

10,225 posts

174 months

Friday 20th January 2023
quotequote all
bordseye said:
Header tank with normal radiator cap - the old metal type. Plastic pipe venting surplus coolant to the ground. But I want to put a catch tank on the plastic pipe so that as the engine cools, its sucks back the water that has overflowed. The installation is in my boat and if the water isnt sucked back then part of the heat exchanger is not covered by coolant and the engine overheats under heavy load.

Question is, with a normal cap and overflow set up, will the engine suck back the coolant from the bottle or will it such air from the atmosphere. Does the cap let coolant return?
I believe this is how it works on my Monaro, and yes, it has a catch tank and the rubber hose that it overflows out of is long enough to remain submerged in the bottom of the overflow tank.

As long as the end of the hose is submerged, it will suck the coolant back in when it cools down again.

As I understand it anyway. Common on classics, for ultimate cool points I believe it is de rigeur to use an empty Jack Daniels bottle as the overflow tank hehe

E-bmw

9,978 posts

159 months

Friday 20th January 2023
quotequote all
QJumper said:
E-bmw said:
Normally the cap works as a pressure relief valve, and that is how is dumps any excess.

As such when not relieving extra pressure it is a closed valve.

Best way may well be to find a newer version of the engine in a newer car that has a more common (these days) expansion bottle set up & replace the rad also.

Obviously is will either need the same hose set up or you will need to adapt them to fit.

Perhaps if we knew the engine it would help with options.
It's in a boat.
I got that, but that doesn't mean it is an engine that only appears in a boat or isn't a conversion.

TwinKam

3,171 posts

102 months

Friday 20th January 2023
quotequote all
Depends on the cap and the filler neck design, eg some caps have a second one-way valve in the top that allows air to be drawn in under vacuum (to prevent hoses collapsing); it would be difficult to adapt that! So as above, it may be best to fit a radiator that was originally designed to work in the way you intend.

stevieturbo

17,535 posts

254 months

Friday 20th January 2023
quotequote all
bordseye said:
Header tank with normal radiator cap - the old metal type. Plastic pipe venting surplus coolant to the ground. But I want to put a catch tank on the plastic pipe so that as the engine cools, its sucks back the water that has overflowed. The installation is in my boat and if the water isnt sucked back then part of the heat exchanger is not covered by coolant and the engine overheats under heavy load.

Question is, with a normal cap and overflow set up, will the engine suck back the coolant from the bottle or will it such air from the atmosphere. Does the cap let coolant return?
Look at your cap and see if it has an ability to allow air/fluid back in.

SystemOfAFrown

59 posts

27 months

Friday 20th January 2023
quotequote all
A system designed to use a header tank shouldn't be dumping coolant out in the first place, unless it's been overfilled or the engine is overheating.

stevieturbo

17,535 posts

254 months

Friday 20th January 2023
quotequote all
SystemOfAFrown said:
A system designed to use a header tank shouldn't be dumping coolant out in the first place, unless it's been overfilled or the engine is overheating.
Yet some OEM do run systems with header tanks, and overflow/return systems

Peanut Gallery

2,523 posts

117 months

Monday 23rd January 2023
quotequote all
As others have said, the old school metal radiator caps do relieve pressure from the rad to the over-flow, under a certain pressure, and then when the system cools it sucks back along the same pipe, using the very center small valve in the middle of the rad cap.

Not that I would ever have experience, but a small crack in that overflow pipe can mean every time the system heats up water is pushed into the overflow container, and every time it cools down air is sucked in. Took a while to find that one!