Venting the skin tank

[Profzarkov]

I've heard that you should vent the skin tank once a year to release any air.

Is this common? I have an Isuzu 42 and can find no vent at all?

Surely the system vents into the header tank?

[Robbo]

2 minutes ago, Profzarkov said:

I've heard that you should vent the skin tank once a year to release any air.

Is this common? I have an Isuzu 42 and can find no vent at all?

Surely the system vents into the header tank?

Both my skin tanks have bleeder valves like on radiators.   Not sure why it would be needed to do yearly tho.

Edited August 21, 2017 by Robbo

[Profzarkov]

Me neither. Mind you I ran my CH and saw that it's header tank was twice the volume, so I bled all the valves on the rads and it's back to normal. Can't see any bleeder valves on mine but then it does go straight into the header tank. The level in this just never changes!

[Tony Brooks]

It all depends upon the design of the cooling system.

If the pipework is such that air can find its way out then you do not need bleed points on the skin tank. Mine does not have any because the header tank is directly above the skin tank and connected by a very large hose. If there is a small hose running from the skin tank or from the top hose that runs downhill to the skin tank (so air can work its way upwards) that runs into a header tank then again you shoudl not need a bleed point on the skin tank. If the top hose runs downwards from engine to skin tank then again a  tank bleed may not be required.

Once its bled then as long as you do not over fill it (so dissolved air enters the system regularly) and the head gasket is not leaking I also can not see why annual bleeding is required. I suspect a system that has too smaller header tank volume for the expansion so it blows so much coolant out it allows air into the tank when cold.

[Profzarkov]

yes, I quite agree, my header tank is much higher than the hoses leading to the skin tank, so any air will arrive at the tank.

i had some friends whose system overheated and even shit off the engine, luckily for them, all their coolant had gone and an engineer showed them how to vent the tank for future reference!

Thanks for the replies. I think no more read?

[bizzard]

More often than not the skin tanks just have a simple little bolt on top to bleed them and not a proper bleed valve.

[Onewheeler]

Mine has a little tap on the top (and the flow from the engine is a few cm below it). It is vented every couple of years when I think about it. At one time we had a BMC1.8 which let gas into the coolant, and it needed bleeding very regularly.

[blackrose]

23 hours ago, Profzarkov said:

yes, I quite agree, my header tank is much higher than the hoses leading to the skin tank, so any air will arrive at the tank.

Yes, most of the air in the skin tank should go the the highest point of the system, but since the pipework connected to most skin tanks doesn't exit at the very top of the tank (but rather an inch or two lower), you might get some trapped air at the top of the skin tank which is why they occasionally need bleeding.