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TR2/3/3A radiator overflow restrictor

deuce

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Hello people.. First good health to everyone in this virus episode. Thank God for my TR3.. so far it's keeping me sane.
Now my question. This has probably been hashed aplenty but can someone please explain the restriction apparently needed when using a more modern thermostat. And, how to do it. I should be getting my radiator back from the rebuild shop shortly..hopefully..
 

sp53

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I have never tried it. I use a sleeve thermostat and a tropical fan. The fan makes a big difference. I believe Macys sells some form of tropical fan.
 

TR3driver

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There is a bypass line from the side of the thermostat housing down to the water pump housing. It allows for some coolant flow through the engine even with the thermostat fully closed (blocking flow through the radiator).

The story is that the original thermostat had an outer ring (aka "sleeve") that moved with the thermostat and partially blocked the opening to the bypass line when the thermostat opened. Some folks believe this action is essential to proper cooling, even though Triumph deleted the sleeve later on, and specified that the non-sleeve thermostat could be used as a replacement for the early one.

My personal experiments with several TR3/As seem to indicate the opposite. Blocking the bypass made no detectable difference in cooling either when I was having cooling problems or when I wasn't. My take is that blocking the bypass probably does increase coolant flow through the radiator by a small amount, but coolant flow is rarely if ever the limiting factor. The pump moves plenty of coolant under all conditions. The main limit seems to be lack of air flow through the radiator; which is exactly why using a more aggressive fan helps so much with overheating problems at idle.

But, if you want to try it, the bypass line is where the restriction goes. I actually tapped the WP housing for a small pipe plug and then drilled a hole in the plug; but Geo Hahn wrote of a better solution. He said there is a copper pipe cap that fits snugly inside the bypass hose (so it won't move around), and you can drill a hole in that. (Sorry, I don't recall the size offhand.)

I use a modern thermostat, with the bypass fully open, and an electric radiator fan. Coolant temperature is much more stable with this setup than it ever was with the original setup and even when outside temps are around 115F (I live near a desert), the gauge never goes any higher than where the fan comes on. The fan only runs intermittently when stopped (or moving very slowly), and not at all above 20 mph or so.
 
Last edited:
OP
D

deuce

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Thanks Randall...Theory and practice..that's what I was looking for. I'll read it about four more times but clear enough. I saw that fan from Macy's. Supposedly bolt on. I'll look at it again
 

DavidApp

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The Roadster factory has a yellow fan that is a bolt on replacement for the metal TR3 fan.

I have the copper cap blocking the bypass tube with a 1/4" hole in if I recall correctly. Using a modern 180 degree thermostat. The thermostat temperature range had the most effect on my temperature. Started off running on the high side. Found I had a 195 degree thermostat installed so changed to a 160 degree thermostat and the TR3 would run at about 160 so I put in the 180 and it stays at that temperature. In the summer in traffic it goes up a bit but comes back down when I start moving. During the cold months I never saw temperatures above 160.

David
 

Frank_D

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I had my rad recored in the fall, I have also received the Macy Hurricane fan which I will install in a few days. Instructions are easy and yes it is bolt on. Quality of the fan is very high. I will install a new 160 thermostat too. The recored rad no longer has the crank hole. The 3/4 in copper pipe end cap that is suggested as a restricter can be done at any time so I will hold off on that. Will let you know how the fan install goes with a couple of pics. Be safe and stay healthy...... Frank D.......
 

TR3driver

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A few other things that might be worth mentioning in this thread :

1) Early TR3A (up to roughly TS40104 per Bill Piggott) did not have the cardboard air deflector between the front apron and radiator. This helps improve air flow through the radiator at higher speeds, and was an approved retrofit to the earlier TR3A. They didn't hold up especially well to age and weather, so are often missing (or unrecognizable). Definitely recommended. Originally supplied in body color, but reproductions are supplied unpainted. The paint helps preserve them, so a coating of some sort of paint is a good idea.
P/N 803440 through 803448. Secured by (4) #8 x 1/2 pan head sheet metal screws and flat washers into the "shelf" behind the grille.

2) Apparently, the factory realized they had a problem, and quietly modified the 3A grille to provide more airflow. It's not clear when this happened, the part number didn't change. The 3A grille was just stamped from flat aluminum, and it appears the change was just to stamp the openings deeper (making them larger). The problem arises because aftermarket (replacement) grilles seem to always be made to the earlier pattern, with the smaller openings. You can find a little more about this (including photos) at
http://www.tr3a.info/FAQ_grill.html

With care, it is possible to work the openings a bit larger by hand. I did mine (back when I ran a 3A) using some wide, flat jaw pliers and working from the back of the grille to pinch each of the slats smaller.

3) The stock TR3 radiator cap will not support a recovery tank, at least I never could find one that would work. The recovery tank is definitely not essential to cooling, although it probably does make a small improvement (by keeping air out of the radiator). Where it really helped, for me, was making it clear when I did and did not have a slow leak. I fought for years with intermittent head gasket leaks on my previous TR3A, that would allow combustion gases into the coolant only under hard acceleration. Without the recovery bottle, you have to leave a large air space in the upper tank (or it just blows excess coolant out the overflow when it gets hot). Adding the bottle made it a lot more obvious I had a problem.

What I finally did was have a radiator shop replace the radiator filler neck with a modern one (cost was under $20 as part of other work they were doing for me); then use a modern cap and the recovery tank from a TR4A mounted down between the radiator and inner fender. It's important, though, to remember that the neck has been changed and not try to use an original type cap. A friend of mine did forget, and his upper radiator hose kept blowing up like a balloon!
P76PBYu.jpg


4) I also had a lot of trouble over the years with the joint between the upper tank and the extension cracking and leaking. Finally had the radiator shop add a reinforcement to that joint, basically just a length of 1/8" soft copper tubing laid into the joint and soldered to both sides, which solved the problem. Once painted, the repair is essentially invisible.

HAoLwE5.jpg
 
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DavidApp

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When I was having temperature problems one of the things I did was to open the grill openings. I believe I saw about a 5 degree drop in temperature from this work. The solution to my issue was the lower temperature thermostat.

In the grill photo you can see the difference in opening by comparing the short slots by the starting handle hole to the rest of the grill. I made a tool to allow me to carefully squash the bars in the grill.
Modified grill.jpg
The tool.
Grill tool.jpg
David
 
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