• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR2/3/3A Thermostat and bypass hose

Share this page

R

RonR

Jedi Trainee
Country flag
Offline
Folks,

Every since the engine rebuild on my TR3A, I have had over-heating problems which have not been solved by a new aluminum radiator and the Macy’s Garage fan.

On the advise of a friend, I have decided to replace my original-style sleeved thermostat with a more “modern” Robert Shaw high-flow thermostat.

My question is do I need to block the bypass hose? My friend blocked the bypass hose on his TR3A by inserting a copper plumbing cap into the bypass hose, with a small diameter hole drilled in the cap to allow some coolant to flow through the copper cap.

Thoughts?
Thanks.
Ron
 
That's what I run...

ynvOFN6.jpg


For many years I used a piece of broomstick... but I think the hole is a good idea.

As I recall, that is a ¾" cap with a 3/16" hole.
 
partially plugging that bypass helps, but is not likely to solve your complete problem. You might start looking at timing or excess fuel issues. I once had a stuck choke that caused my TR3 to overheat. Lots of possibilities.
 
Thanks, Charley.

Initially, a too far advanced timing appeared to be the problem, but correcting that did not make any difference.

But, I will recheck both the carb setting and timing.
 
Normally advanced timing helps the engine temperature stay lower, while retarded timing tends to increase heat in the engine.

I doubt the thermostat will help, but there is a chance the one you have is defective, so you never know!?! If the car overheats while driving, I would suspect a problem with the water pump. It is easy to get the clearance on the impeller to large during a rebuild so the water cavitates and flow is reduced. Another possibility is one of the intake hoses is collapsing at higher rpm, to also reduce water circulation.

If it overheats while idling, and you have the factory ducting installed...then the only options are to increase airflow with a tropical style mechanical fan, or an electric fan. These cars tend to be air flow limited, so they will overheat if allowed to idle with no forward motion. An electric fan often requires an alternator upgrade to handle the amperage requirement.

There are other reasons for an overheat, but I’ll not mention them, since you just rebuilt the engine and I’ll assume it was cleaned properly in the rebuild.
 
The thermostat is relative new; one of the very expensive Moss 160 degree sleeve-types.
The water pump was replaced about 18 months ago using a unit from The Roadster Factory. I remember discussing the pump with Albert at TRF, as he did not have an original pump in stock. If my failing memory is correct, the new pump has an additional blade as compared to the original pump.

I will check the hoses.
The car does not overheat at idle and cool down when driving. The problem is overheating while driving.
The engine block was tank-cleaned by Farley Engines (now retired).
 
Another option is to have an original pump rebuilt by The Flying Dutchman Shop. Look him up online and watch his video on u-tube. He explains how the stock impeller has too much clearance to efficiently move enough water especially when idling. I sent him my water pump last week thinking it was a stock unit but he called me and said it was one of a few aftermarket units being sold and that it was a 6 blade impeller and had a sealed bearing on the shaft. He advised me that the impeller on this new aftermarket pump didn’t come close to matching the shape of the housing and it was probably as bad if not worse than the stock Triumph pumps. He has never rebuilt one of these aftermarket pumps but he was going to tear mine apart further and see what he could do. The other option was to use an old original core and rebuild it to his clearances. I am waiting on his call. I have read posts on this on here and other forums and everyone was happy with the results of his rebuilds. Makes sense to me more water flow equals lower temperature. You already have done the upgraded radiator and fan which again alone has helped a lot of cars control overheating. Maybe it’s your aftermarket water pump. I will post again when I hear back from the Dutchman.
 
With a 160 degree thermostat it may be allowing too much flow so that the coolant does not stay in the radiator long enough to be cooled before returning to the engine. A 180 degree thermostat might help. I have run into this in a high performance 4 cylinder Toyota my brother had years ago. I don't know if the same principle applies to the Triumph engine. There is a lot involved in cooling an engine.. I am sure you will find the culprit to you over heating problem as you weed thru suggestions from the vast knowledge of the forum. Frank
 
Are you sure that the thermostat is the culprit. Are the 3A cardboard shrouds in place - essential in my opinion. Are you sure that the cooling system does not have an airlock?
A visit to the TR register site will give you some useful suggestions.

james
 
To Frank's suggestion that water is moving too fast and not picking up enough heat, this hypothesis has some appeal and has been broached before on this Forum. As TR3 driver pointed out in a thread titled "TR3A running hot at high RPM" started 6/20/18, the 1st Law of Thermodynamics seems to preclude this result.
Bob
 
If it's under motion only, I would check the intake hoses for collapse under high suction. That is the number 1 most likely cause. The water pump is still a possibility if it is cavitating...with the low quality of parts we have been seeing, "new" is meaningless when trying to diagnose anything. A simple cause would be if the radiator cap is not holding at 4psi, and is venting lower than that. Lower pressure result in lower boiling point. Once it boils over the temp will spike. The radiator ducting is also a simple way to improve moving temperature.

Of note, I hot tanked my block, which was wonderful in removing the grease and dirt build up. It did nothing for the rust scale in the cooling area of the block. It doesn't seem to help with rust scale at all...and that was the cause I refrained from mentioning above for a new rebuild.
 
Thanks everyone.

I an not sure it is the thermostat but everything else seems to be correct.

It overheats at highway speeds.
The radiator shroud is new and correctly installed.
The radiator and heater hoses were all replaced when the engine was rebuilt, about 3 years ago.
The radiator cap was new at the time of the engine rebuild.

I agree new does not mean good. I try to avoid buying parts from my semi local British car parts place because I end of returning at least half of their parts.

Ron
 
When you say over heating how high is it getting? Is the gauge accurate?

I had a similar experience last year. Went through most if not all the things you tried. I was running at about 200 degrees f +
It turned out I had a 195 degree thermostat installed. When I put a 180 degree thermostat in that brought the temperature down to about 180. In fact during the cold months it ran at about 160 degrees.

David
 
Hi David.

The car runs between 195 and 200 degrees F, which seems very high to be since it has a 160 degree thermostat installed.
 
Back
Top