John,
One of the short comings of the TR3 and TR4 cooling system design is the
inability of steam to escape the system. Once formed, it creates hot spots
and air has replaced water in the area steam has formed if you don't give it
a path to escape. The fact that the thermostat housing is typically the
high point of the system doesn't help. Another problem is lack of flow to
the back of the head and to piston #4.
I started down a similar path as you suggest. I assumed that if I routed
hot return water back to the suction side of the water pump (return heater
port) I'd be recirculating hot water and this would be bad. So for my
system, I installed a expansion tank with a 22-25 psi cap on the firewall
routed the heater supply (port on back top PS of head) to the top side port
of the tank and routed the return line from the bottom of the tank to a
fitting I installed between the thermostat housing and the intake of the
radiator (I run a Chevy style cross flow radiator read more later). This
allowed the hot water from the back of the block and head to return directly
to the radiator and be cooled prior to go back through the engine.
This seemed like a great idea. I now had a place for steam to collect (the
expansion tank) and I had increased the flow to the back of the head and
block. Only problem was it worked too good. Even with a 180 degree
thermostat, I could not get any heat into the engine it was running less
than 120 degrees.
The system simply bypassed the thermostat as all water was flowing from the
back of the head through the tank and back to the radiator. I had bypassed
my thermostat. I thought about playing with various restrictions in my
return line but figured that the correct restriction would likely change
based upon conditions.
So I scrapped my idea and plumbed my return line directly to the heater
return port. Works like a champ now.
I mentioned that I use a Chevy style cross flow radiator. This design has
several advantages to the top to bottom flow of our standard radiators. The
problem with a top to bottom design is that the radiator is seeing block
pressure on the top of the radiator which means your radiator cap is seeing
full block pressure, or very close to it. I have not put a pressure gauge
on my block but I have read that block pressure can reach 30 psi. For this
reason, some TR racers are always pumping at least a little water past their
caps on a top down style radiator. With cross flow, the radiator cap is
kept on the suction (low pressure) side which allows a low rated cap, I use
a 7 or 12 psi cap in the radiator, can't remember exactly.
More on expansion tanks. Do a little research and you will find that most
if not all modern cars run stem vent tubes from the cylinder heads or other
high points to an expansion tank. A good example is the Gen III & IV small
blocks.
I also use a 1/4 npt drain valve on the top of the thermostat housing to
vent all air out of my system when filling, this is very important. I use
the expansion tank as the fill point and fill until the water leaks out
through the open 1/4" valve. I prime the system a little by squeezing the
house on the intake side of the water pump as I fill the system. Once all
the air is out, I close the valve and fill the expansion tank to within 1/4"
of the top. So far, one race weekend, I have had zero water pump past
either of my caps with this installation.
My dad is using this same setup but with a Wizard top to bottom radiator.
He was getting a little water past the cap on the radiator cap and the
expansion tank cap. He was using a 12 psi on the radiator and 18 on the
expansion tank. He has replaced the caps for higher rated ones so we will
see how it goes at ECR in May.
Bob Kramer has been using this setup with a top down radiator for a few
years. I think in a 15-20 min race he fills his expansion tank overflow
bottle but he is using a lower rated cap I think it was 12psi. I have tried
to convince him to switch to a higher pressure rating on the expansion tank,
we shall see.
Let me know if you want more information or pictures.
Greg
04 TR3
-----Original Message-----
From: fot-bounces@autox.team.net [mailto:fot-bounces@autox.team.net] On
Behalf Of John Wagner
Sent: Monday, March 18, 2013 2:27 PM
To: Fot@autox.team.net
Subject: [Fot] cooling
Amici
I am thinking of running a tube from the heater outlet to the front of
the engine.
In past threads it said to connect it to the water pump inlet (heater
return) that is just taking hot water and returning it to the engine,
wouldn't it be better to plumb it to the thermostat housing and on to the
radiator?
Thank you
Just the wrench
John Wagner
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