S1: Purpose of header tank connections?

E-Type
1

Please pardon my ignorance but I know NOTHING about Series 1’s.

What is the purpose of the header tank pipe connections. The 4.2 I’m helping a friend with has 3 connections:

  1. large pipe from engine to header tank;
  2. large pipe from header tank to left of radiator
  3. smaller pipe from header tank to right of radiator

I presume:

  1. obvious, feeding hot coolant (once thermostat is open) to the header tank;
  2. feeding hot coolant from header tank to input side of radiator?
  3. ??? This pipe has me baffled.
2

I found a thread that discusses that 3rd pipe and it seems to be a mystery indeed…

09 discussion

3

I found a post on the UK forum but sadly the pics no longer show (dropbox again I’m sure). I duplicate here to some extent with thanks to ada5.

Anyway, the text goes a long way to explain:

  1. Pipe from engine thermostat housing goes via a pipe internal to the header tank, directly to top-left of radiator. This pipe has a small opening on the side where the otter switch protrudes into it to sense the coolant temp (for fan control) but apparently, does not seal 100%. Small amounts of uncooled coolant and air can thus escape from this opening into the header tank.
  2. The smaller pipe from the right-front that goes to the top right of radiator, serves to allow expanding coolant into the header tank and provide a path for air trapped on the RH side of the radiator to the header tank. I have read of owners blocking this pipe off… not ideal IMHO.

Aftermarket header tanks caution:
It seems that aftermarket header tanks might have the opening for the otter switch too large which would result in the creation of a permanent bypass circuit for coolant to bypass the radiator: From engine pipe internal to header tank (high pressure), out the otter switch hole, to the RH side of radiator (low pressure) via the smaller pipe and back to engine - rendering the cooling system less efficient.

4

Philip I assume by your question: “2. smaller pipe from header tank to right of radiator” you are referring not to the even smaller tube from the manifold to the right side of the tank but to an actual hose from the header tank. The header tank hose on the right is for filling the radiator from the header tank and nothing else. The other large hoses on right and left side connect to a through pipe in the tank that is not open to the header tank, and takes water directly from the manifold to the rad top left.

5

I presume you meant: “to the right side of the radiator”? I understand that this even smaller pipe from the manifold to the radiator is meant for the coolant bypass circuit if the (correct Smiths #85025) thermostat is closed.

So, yes, I was referring to the smaller pipe from the right side of header tank to the right side of the radiator. Since there is no real connection from the header tank to the pipe that runs directly through it from manifold to radiator left side, the smaller pipe I was referring to is indeed the only pipe that can allow the cooling system to be filled - thus its MAIN purpose. I HAVE read about people blocking this pipe!!! :roll_eyes:

6

[quote=“jagwit1, post:5, topic:361660”]
…the smaller pipe I was referring to is indeed the only pipe that can allow the cooling system to be filled - thus its MAIN purpose. I HAVE read about people blocking this pipe [\quote].

By this logic the 3.8 cooling system, which has no such pipe, could not be filled…

Likewise, a 3.8 where the Otter bulb fits exactly into the side of the through-pipe could not fill the tank with expanded coolant.

Since both phenomena do in fact occur, it’s back to the drawing board chaps.

IMO the small 4.2 right tank to right rad hose is simply a convenience for filling. When the waterpump is running the bulk of the coolant flows along the internal pipe from rear right through to forward left as in the 3.8. Leakage past the Otter bulb into the body of the expansion tank allows the hot coolant volume to increase into the head space where it effectively ceases to be part of the main coolant circulation.

7

There MUST have been openings from the right rear- left front internal pipe to the3.8 header tank then - as some posters reported. To fill coolant poured into the header tank must have found its way into the the through pipe and thus into the radiator. The bigger question then is how air trapped (on RHS) in the 3.8 radiator got out to the header tank…

What we need to settle this mystery is for someone with a rotten 4.2 header tank to cut it open and post pictures of the insides for us. PLEASE, with a cherry on top.

Sounds like you are agreeing then Peter?

  1. it is used mainly for filling the cooling system -more so if coolant can not readily flow into the through pipe inside the header tank;
  2. if coolant can flow INTO the radiator via the front right pipe, air can also flow through the pipe (in any direction);
  3. since the RHS of the radiator has a lower pressure than the LHS of the radiator (waterpump sucking on RHS and pumping to LHS), it follows that coolant escaping from the through pipe into the header tank (where higher pressure exists than on RHS of radiator), such (hot) coolant will bypass the radiator.