Hi,
Sounds like you are on track with this. I do think TRs were sort of under-engineered for cooling, probably because the British climate is seldom very toasty and certainly not arid.
What sort of thermostat are you using? Is it a sleeved one?
These are harder to find and a lot more expensive than the common type found at most auto parts stores. (Last time I checked, Moss and The Roadster Factory has them.) But, a sleeved t'stat is specified for TRs and is important, because otherwise the bypass hose will tend to route too much water right back into the engine before it goes through the radiator and is cooled. As it responds to the engine warming up and opens, the sleeve on the t'stat gradually covers up the bypass hose opening.
It *is* possible to use the cheaper, common type of t'stat from your local auto parts store, but the bypass hose needs to be partially blocked off in a somewhat permanent manner. To do this, find something to make a plug that fits inside the hose pretty tightly, then drill a 1/8" hole in that plug to allow some small flow of coolant. Also check that the t'stat has one or more relief holes in it, to allow some pressure through even before it starts to open. (Some cheap ones don't have these holes, in which case 2 or 3 1/16" or slightly larger holes can be carefully drilled and positioned near the top when the t'stat is installed, because these holes also help to purge air from the system when it's being filled.) Personally, I've never felt totally comfortable with this setup and just prefer to use a sleeved t'stat, even though it costs 10X as much and can be hard to track one down! I think there was a Rover or Land Rover using a sleeved t'stat that will work, but haven't been able to confirm this yet.
By itself, a 160 degree t'stat won't actually help resolve overheating problems. The thermostat's rating only relates to what temp the t'stat is fully open, but 160 or 180 should both be fully open and flowing the same amount of coolant at normal operating temps of a TR 4-cyl. engine. (195 "winter" t'stat might be another matter, since it's up close to or just barely within the normal operating temp range of the engine.)
If changing to a 160 happens to make a difference in terms of overheating, that just means the old t'stat was going bad and not fully opening. A new 180 working properly should give the same result. A 160 degree t'stat normally wouldn't hurt anything, will just make the engine warm up more slowly and might drop it a little below "normal operating" temps occasionally. But, that's not usually a problem on TRs, as you know!
You probably also already know, TRs shouldn't be run without a t'stat installed. I've heard it explained that without the slight restriction of the t'stat, coolant pushes through the radiator too quickly, not giving it enough time to cool down. I don't know if this is true or just someone's guess.
But, at any rate, the cars do tend to overheat when no t'stat is used. Racers often don't use t'stats, but also had overheating problems when they left them out of TR 4-cyl. engines entirely. So, a common racer trick is to just heat up the t'stat in a pan on the stove, until it's fully open, then break and jam it in the open position.
Other things you might want to check or consider:
- Insure all air is out of the cooling system. One thing that helps is to jack up the front of the car a bit when filling the coolant, to raise the radiator well above the engine. (I've also seen air relief valves installed in the thermostat housing and/or the heater valve area, to better allow trapped air out.) The 4-cylinder TRs are pretty good at purging air, but it's something to watch out for.
- Is all the radiator shrouding in place? This is perhaps more critical on TR4-6, but is also important on TR2/3s.
- Have you replaced the radiator cap recently? They do get old and tired, need to be replaced occasionally, same as t'stats. Just be sure to get the right cap, which is 4 lb rated on TR3 if I recall correctly. (Note: if your car *doesn't* have a heater installed and the radiator is in good condition, i.e. has been pressure tested by a radiator shop recently, it can help a lot to go to a TR4's 7 lb. or even higher pressure rated rad cap. Higher pressure in the cooling system will help it work more efficiently. The heater core is the limiting factor in TR3, and TR4 for that matter. By TR6, Triumphs were using 12 lb. in the cooling systems. Some modern cars use 20-22 lbs or more.)
- Is there any possiblity a radiator hose is collapsing? Old hoses sometimes do this. Usually it happens with longer hoses, which might be one reason why Triumph used a metal pipe with two short hoses at the bottom of the radiator. If you have the original hose arrangement, it's unlikely, but something that might be worth checking.
- Are you mixing coolant 25% anti-freeze, 75% distilled water? This will give better cooling than the usual 50/50 mix recommended. (A mixture with more anti-freeze should be added to protect from freezing in the Winter, the exact ratio depends upon climate, storage and usage of the car.)
- Has the radiator been repainted lately? If so, was special "thin coat" rad paint used and the old paint removed first, or is there a build-up of layers of thick paint? Thick paint can really reduce radiator effectiveness. Once source I know of, which sells radiatior paint that covers completely with a very thin coat, is Eastwood Co.
- Does your radiator have the crank hole in it? If so, this reduces radiator effectiveness by about 20%, but blocking of a significant number of the internal passages. About thhe only way to resolve this is to have the radiator re-cored without the hole.
- Has the radiator ever been re-cored? It's not all that expensive and most local rad shops can do it for you. Talk to them, they might also be able to suggest some upgrades that add little cost and look original.
- A second or even third engine flush, perhaps with a proper flushing additive this time, might dislodge some more rust or crud in there. Unfortunately, there's not much more that can done for the internal engine until the next time it's rebuilt.
- Try Redline's "Water Wetter" or other coolant enhancements (DEI and others offer them, too). Some folks report these help a bit.
In addition to the possible TR6 fan or electric fan, you might consider:
- Install an improved, 6-vane water pump (Ken at
www.britishframeandengine.com sells them, among others). This will move more coolant through the engine. These aren't cheap, but will likely help. The special, 6-bladed rotor in these pumps was primarily designed for racing, to reduce cavitation at high rpms (this is basically where the impellor is spinning so fast that it causes the fluids to stand off and creates a sort of "bubble" around itself, so really isn't moving the coolant much or at all). But, it is simply a better made and more effective design that can help at lower rpm ranges too.
- Another option is to install an oil cooler. Oil helps cool the engine, too. If this is done, be sure to use a thermostat for the oil cooler, too (usually 185 degree) because overly-cooled oil can be just as bad for an engine as overheated. A 10-row cooler is generally adequate for the TR engine. But, alternatively, 13-row and 16-row are sometimes used.
- Vent the engine compartment somehow. I'm not sure the best way to do this on a TR3, probably louvers in the hood would be about the only option. TR4s can use fender vents. Some other Triumphs (and many other cars) came with vents installed. Not only does this reduce underhood temps by allowing the hot air to escape, it allows a higher volume of air into the compartment (where it normally "dams up" at speed).
- Install a "header tank" for the radiator, which is something found on nearly all modern cars and is not the same as an overflow tank.
- If you do install an electric fan, a "puller" mounted behind the radiator is more effective than a "pusher" installed in front (and hidden by the shroud). This is because a fan in front of the radiator actually blocks some of the flow, even when it's running.
- If you do mount an electric "puller" fan behind your radiator, the original fan will need to be removed. Don't remove the fan extension hub, though. It also acts as a sort of dampener for the crankshaft. (It can be replaced with a true, harmonic dampener, though, if you wish).
/ubbthreads/images/graemlins/cheers.gif
Hey there Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
A friendly reminder - be careful what links you click on here. If a link is posted by someone you don't know, or the URL looks fishy, DON'T CLICK. Spammers sometimes post links that lead to sites that can infect your computer, so be mindful what you click.