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Re: Blocking the Bypass

Subject: Re: Blocking the Bypass
From: Chip Old <>
Date: Wed, 27 Sep 2000 23:38:08 -0400 (EDT)
On Wed, 27 Sep 2000, Scott Allen wrote to

> I'm finishing up on my TD's cooling system, and have the thermostat
> off the car.  As such this would be the time to consider blocking the
> bypass.  I remember there being some discussion about this in the
> past, and have searched the archives which indicates that doing this
> is a bit controversial.  I need to know from the listers why it's
> desirable or undesireable to do this, and the best way to do it if I
> decide to go ahead with it.

You didn't say what type of thermostast it is, and that has a bearing on
the answer.

If it's the original bellows-activated type with a bypass sleeve valve,
and if it still works, put it back and don't worry about the bypass.  When
the thermostat is closed the bypass will be open, routing coolant through
the engine but not through the radiator.  When the thermostat is open the
bypass will be closed, routing all coolant through the engine.

If it's a replacement housing or an original housing modified to use a
modern pellet-operated thermostat, then either leave the bypass unblocked,
or (better) reduce the bypass passage to a 1/4 inch diameter hole.  There
are a number of ways to do that, but the simplest is a plate between the
housing and the bypass elbow with a 1/4 inch hole drilled in it.

Don't block the bypass completely.  If you do, when the thermostat is
closed there can be no water circulation through the engine.  That can
cause localized hot spots.  That might not cause any immediate problems,
but over the long haul it will contribute to short exhaust valve seat life
and faster cylinder bore wear.

Others here will disagree, so now I'll step well back and watch the fun...

Chip Old               1948 M.G. TC  TC6710  XPAG7430  NEMGTR #2271
Cub Hill, Maryland     1962 Triumph TR4  CT3154LO  CT3479E

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