Hi Randall
Are you really suggesting NOT to put a restrictor in the bypass line? What
would TeriAnn say? ;) Here's my 2.5 cents:
Sleeve or no sleeve, the thermostat's job is to minimize flow through the
radiator when it's cold, while allowing some circulation through the engine in
order to avoid hot spots. In a sleeved system, both the radiator and the
bypass circuits are flowing when cold; the sleeve shuts off the bypass circuit
as the car warms up so that all the water goes through the radiator. In one
type of non-sleeved system, only the bypass circuit is flowing when the car is
cold; as it warms up, the thermostat opens the passage to the radiator and both
circuits operate. The two designs are clearly different. The sleeved system
relies on the resistance of the radiator to force most of the flow through the
bypass circuit when both are open (cold); therefore, the bypass line must be
unrestricted. The non-sleeved system relies on the resistance of the bypass
circuit to force most of the flow through the
radiator when both are open (hot); therefore, there the bypas line must be
restricted. (Note: There is another type of non-sleeved system, not relevant
to this discussion, in which there is no bypass circuit, just a small hole in
the thermostat allowing some flow to prevent hotspots when the thermostat is
closed).
Assuming the TRactor engine's cooling system was engineered correctly in the
first place (and that's a pretty big assumption), you should have to
re-engineer the system by adding a restrictor to the bypass circuit when
changing to a sleeveless thermostat. Otherwise, most of the flow will continue
to bypass the radiator even when the car is warm and the thermostat is wide
open, leading to overheating.
Is the restrictor really necessary? Is the unrestricted bypass line really
so unrestricted? Did the engineers get it right? 40+ years on, the answer
probably varies from car to car depending on how much gunk has built up in your
bypass line. Adding a restrictor is simply erring on the "safe" side. And as
Randall points out, it probably doesn't matter whether you add one or not if
you upgrade to a decent fan. But it can't hurt.
-Nick
> Date: Sat, 22 Oct 2005 18:06:10 -0700
> From: "Randall" <tr3driver@comcast.net>
> Subject: RE: thermostats
>
> Well, all I can say is that I tried [installing a restriction in the bypass]
> and it made no detectable difference for me. If it was going to make a
> difference, I would think the difference would have to be at idle where water
> flow is much lower, but a decent fan solved that problem for me (which again
> suggests that lack of water flow is not the problem even at idle).
>
> ...
>
> Could be that someone didn't do their homework, and just assumed that
> the bypass had to be blocked. Many if not most cars do not block it ... just
> look at all the thermostats at the local parts house that don't have blocking
> plates on them. They all have bypasses. And apparently Triumph/BL later
> decided that it did not have to be blocked. TR250 & 6 did not, for example.
> And while the TR7 did (probably due to persistent overheating problems), I
> suspect the TR8 did not.
>
> Randall
=== This list supported in part by The Vintage Triumph Register
=== http://www.vtr.org
|