[Healeys] Coolant bypass port in the head - 6-cyl

Tue Mar 29 20:50:04 MDT 2022

Hi all,

FYI, Norm Nock did a nice write up on the thermostat issue in his “Tech Talk” publication complete with diagrams.  He notes that a “new” (back in 2009) thermostat was available with the sleeve and it moved down as the operating temp was reached.  I bought one from him at British Car Specialists and have had no issues at all.  No idea if BCS still carry them.  It is worth buying a copy of Tech Tips too – lots of interesting information there!

Cheers, Mirek

From: Healeys <healeys-bounces at autox.team.net> On Behalf Of Alan Seigrist via Healeys
Sent: March 29, 2022 10:00 PM
To: Bob Spidell <bspidell at comcast.net>
Cc: Healey list <healeys at autox.team.net>
Subject: Re: [Healeys] Coolant bypass port in the head - 6-cyl

Hi Bob -

the Robertshaw thermostats are nicely made, but they open the wrong way around... let me do some measurements as I am dealing with the cooling on my BJ8 now.  I have a robert shaw... as well as another sleeved thermostat as well as the bellows.

Best,

Alan

On Wed, Mar 30, 2022 at 9:54 AM Bob Spidell <bspidell at comcast.net <mailto:bspidell at comcast.net> > wrote:

Years ago, someone--might have been BCS, but I'm not sure--was selling a Robertshaw thermostat with a brass sleeve soldered to it (Robertshaw thermostats have a center portion that moves up and down). The one I bought was 160deg; I desoldered the sleeve and soldered it to a 180deg Robertshaw. I bought one of the original, bellows-type from Kees--whatever happened to him?--but never installed it; heard they were the 'fail closed' type, which could turn a minor failure into a catastrophe (still have it around somewhere).

https://flowkoolerwaterpumps.com/products/robertshaw-330-160-degree-thermostat

On 3/29/2022 6:35 PM, Alan Seigrist via Healeys wrote:

Harold - 

Thank you, now I understand how the whole thing is supposed to work.  The sleeve works to cut off the bypass so that hot water is not recycled into the system after it warms up.  FWIW, this only applies to the 6 cyl, the 4 cyl doesn't have any sort of bypass.

Yes, I think it would be great if you could share with us which thermostat to purchase and how to modify it.

Best,

Alan

On Wed, Mar 30, 2022 at 1:28 AM Harold Manifold via Healeys <healeys at autox.team.net> wrote:

The coolant bypass plays an important but problematic role in the Healey’s cooling system. When the thermostat is closed coolant returns to the water pump via the bypass. See the red circle on the attached picture. The bypass is important for three reasons: its allows the coolant in the block to continue to circulate and come to a uniform temperature before the thermostat opens, it prevents hot spots that could develop from stagnant coolant and it prevents the water pump from dead heading.

The problematic part is in the original design the bypass was closed by a sleeve on the bellows type thermostat when the thermostat opened. The original Bellows type thermostat used a volatile liquid and were not reliable and were not suitable for the 7 psi cooling system pressure. Wax type thermostats are much more reliable but they do not have a sleeve to close off the bypass. There may be some expensive wax type replicas of the original bellows type.

After looking at many options the best option for a reasonably priced wax type thermostat with a sleeve to close off the bay pass is the modified Land Rover Series ll thermostat. If anyone would like to know about modifying the Landver thermostat let me know. It can be easily done.

Harold

From: Michael Salter via Healeys <mailto:healeys at autox.team.net> 
Sent: Tuesday, March 29, 2022 9:17 AM
To: Healey list <mailto:Healeys at autox.team.net> 
Subject: Re: [Healeys] Coolant bypass port in the head - 6-cyl

The coolant travels from the bottom of the radiator to the water pump into the block then from the block into the head then through the thermostat to the top of the radiator.

M

On Tue., Mar. 29, 2022, 11:57 a.m. Elton S, <eps2660 at gmail.com <mailto:eps2660 at gmail.com> > wrote:

As a related question, what is the direction of flow through the radiator - up from the bottom or down from the top?

Elton  

BJ7

On Tue, Mar 29, 2022 at 11:44 AM Michael Salter <michaelsalter at gmail.com <mailto:michaelsalter at gmail.com> > wrote:

As Gary points out, and far as I have been able to figure out, the bypass passage is open when the engine is cold, the idea being that by "short circuiting" the radiator the coolant in the heater and bypass passage will warm up more quickly and the heater will produce heat more quickly. 

We had a slew of the "shrouded " type thermostats that I bought when Smiths Canada closed down. The part number was 43570/28 and we used to sell them to customers who reported overheating problems. 

I stopped promoting them as a potential solution to overheating issues after being taken to task by a customer who did an extensive study of the issue and proved, at least to my satisfaction,  that they improved cooling not one iota.

M

On Tue., Mar. 29, 2022, 10:47 a.m. Alan Seigrist, <healey.nut at gmail.com <mailto:healey.nut at gmail.com> > wrote:

I don't know if this has ever been answered before, but where does the little bypass port begin?   

What parts of the head does that bypass come in contact with? 

When do you want to cover the port with a sleeve (when coolant is hot or cold?)

I ask because the old bellows style thermostat will cover the bypass port when the thermostat opens

then I have another wax thermostat and the sleeve actually cover the bypass when it is cold, and doesn't cover it when the thermostat opens.... so it works exact opposite to the old bellows style thermostat.

confused....

Cheers,

Alan

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