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Re: water by pass

To: "" <>
Subject: Re: water by pass
From: David Massey <>
Date: Fri, 14 Dec 2001 11:33:31 -0500
Cc: "[unknown]" <>, "[unknown]" <>
Message text written by
Anyone know how this story is substantiated?  The factory connection ?  I'd

never heard it till lately, but I've only been fooling with the 4 cyl since

64. The early TR2 had a problem keeping an intact head gasket that was 
supposedly a factory problem fixed in the early day. I seem to remember all

the steam logic being developed . piece by piece, pretty much right on this

list.  Sort of a leg bone is connected to the hip bone sort of story.  I 
particularly like the part about the steam and the T-stat. I guess the next

logical step is that the steam gets into the radiator and sprays unwary 
pedestrians.   Any other early marques have a similar bypass? I'd guess any

good  physicist interested in thermal dynamics would lay this story low.


A close inspection of the TR6 water pump housing will reveal a small
passage between the water discharge and water inlet.  For those not
familiar with the SC engine cooling system, the coolant ingress and egress
passages are side by side on the front of the cylinder head.  The water
pump housing not only comprises the cool side radaitor hose connection and
water pump but the thermostat housing as well.  There is a small (approx
1/4 or smaller) passage between the discharge passage (before the
thermostat) and the pump inlet.  The purpose of this port is uncertain to
me.  It may be to aid in bleading air from the system when filling.  It may
be to provide for some circulation when the thermostat is closed  (although
the intake manifold preheat may be sufficient for this purpose).  (I don't
recall a manifold preheat provision on my TR3)

But since the thermostat responds to the temperature of the coolant -at the
thermostat- if the coolant is not circulating then the thermostat will not
open until such time as convection currents and conduction eventually carry
the warmth that far.  I remember, many years ago, watching my MGB come up
to temperature.  The temp would rise up to a point about 10 or 15 degrees
above the thermostat opening point and when the thermostat eventually did
open the temp would drop to the thermostat operating point and remain there
the rest of the run time.

If you look at the thermostat housing on the Vangard engine you see it
stands proud of the engine.  In cold conditions, if the car is at speed,
the surface cooling on the thermostat housing could keep the thermostat
from opening for quite some time if it were not for the circulation of the

I don't know anything about the steam theory but perhaps the uneven heating
was sufficient to cause the rash of head gasket failures and uneven heating
is reduced by circulating the coolant.  If steam were to develop it would
accumulate in the head and seek out the high spots.  This would be the
thermostat housing where the steam would cause the thermostat to open. 
Remember these engines are only one step removed from the thermosyphon
models of earlier years.

The recommended modification for running a non-skirted thermostat is to
block off the bypass with an orifice (a plug witha small hole drilled
through).  This will provide a small amount of circulation but will not
significantly diminish the flow through the radiator (after all, the skirt
doesn't block off the bypass 100% either).

All I can say is the folks who designed these cars weren't stupid.  And
they didn't put these things in just to aggravate owners.  These things
were installed for good reasons and unless one has a good understanding of
how these things work removing these features can yield unexpected

Best regards

Dave Massey
St. Louis, MO USA
57 TR3
71 TR6
80 TR8

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