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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 157
Registered: 07-2023
Posted on Tuesday, 21 May, 2024 - 05:26:   Edit PostDelete PostView Post/Check IP

My S thermostat has been damaged unfortunately. I can confirm when the brass bellow is damaged enough to cause it to absorb water, it does not work anymore. Even after the bellows have been straightened.

I'm not entertaining $850 for a RR-B spares one.

So my options are to replace with a modern normal, or high flow thermostat, with or without a bypass hole. $45 A high flow variant is appealing as larger volumes of water turning over in Australia's summer can't be a bad thing.

Another brass one that fits something else > $150

Or perhaps replace the existing brass bellow with a new one. I see they are around, but all I can find is in volumes of 100+ to buy. So if you know of a retailer please share. Also any reports or experience in replacing the bellow, perhaps more so if its a reliable venture. The OE looks simple enough with a soldered nut which locks a dial that adjusts the opening temp. I see there is also scope for a little porting to increase flow if desired.
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 637
Registered: 07-2018
Posted on Tuesday, 21 May, 2024 - 08:39:   Edit PostDelete PostView Post/Check IP

Jason !

I'm not sure what page you're looking at, but they're not that much.

An after market one is 384.97 Australian dollars.

You need the one to shut the by-pass port on hot days, or even mild days.

A modern one with no means to shut the by-pass port off is not a good thing with these engines __ as you know.

Just bite the bullet.

A modern type with a wax pellets as opposed to the bellows type is far more reliable and accurate anyway.

The one from Flying Spares is the wax pellet type with the proper by-pass port.

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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 158
Registered: 07-2023
Posted on Wednesday, 22 May, 2024 - 05:18:   Edit PostDelete PostView Post/Check IP

Ta mate, still dumb though isn't it at $384. $700 for the genuine and both still need tax and shipping.

I see a Jag XK120-150 is half the price. And if you prefer MG one can be sort for $30

I found one of these old jiggers like mine but waiting on a price.

Trouble is, and petty as it is, the above are all 78c and mine says 72c. Perhaps odd for a home market car and I presume a thermostat that looks like that is original. I understand lower opening temperatures is good for warmer climates such as Australia, but mines not an Aus import. Though we get to 3c around here for winter, add a 0 for summer then some and that's when a car needs its cooling the most.

I guess with time and technology, improvements on things like tyres, seals, bushes, upholstery underlay are all possible improvements on what was used back then, and I have gone that route. I have plenty of hills around me also so opening early and high flow is attractive. I know I seem scabby, but it just so happens the probable winner is also a reasonable price, then even more so for a part no one sees.

Jeff, would you be agreance the jiggle pin on a modern thermostat addresses the bypass? Or could you remind me why the bypass is what it is. I was sure I read an article suggesting a bypass was a must, and drill your own if it don't have them. There was no open or shut, just open.
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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 159
Registered: 07-2023
Posted on Wednesday, 22 May, 2024 - 06:32:   Edit PostDelete PostView Post/Check IP

To add Jeff, think I'm going to pressurise the system also. Under 7 psi I believe.

I understand it removes the need to check water all the time and gives the system breathing room.

My FIL will say why bother if the system is clean and working, however his cars are not seen to be used as a daily.
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 638
Registered: 07-2018
Posted on Wednesday, 22 May, 2024 - 15:23:   Edit PostDelete PostView Post/Check IP

I just got used to paying a bunch of money for things, I did modify a bellows thermostat with a modern wax pellet sensor, used it for years, but the car always ran cold.
The wax unit ended up being to low in the thermostat housing and it never got to temperature.
Bloody cold late in the season, right around Halloween.

I even bought a new heater matrix as all the old dinner plate types always leaked.
I spent a huge amount of time fitting one in out of a Morris Minor (it was much bigger) and had good heat for a while _ until it started to leak.
All that bother for nothing; my time is worth something to me, in the end I just should have bought a new matrix, the same with the thermostat, but to be fair, I got one from eBay for 150.00.
Same with tires.... All the money I wasted on tires that really didn't suit the car, and I was never really pleased.

The jiggle valve (the small hole in the thermostat) is just there so air can escape while the system is being filled, it has nothing to do with keeping the car cool or hot.
Circled is the by-pass port, and in your photo it's almost closed off by the bellows (which is not normal, that thermostat you have there is shot, the top is missing too).
When the car is cold, coolant flows through that port and recirculates through the engine, and not the rad _ this helps to warm up the engine.
As the engine gets hot, the bellows closes the port as it grows so most of the coolant flows through the rad.
The problem here is that I don't believe the bellows actually closes all the way, so all the coolant never goes through the rad. With the wax type it doesn't take the car over heating before the port is closed right off, it's much more efficient too and reacts quicker as well.
My opinion is that the 72 is too cold, it's not good for any engine to run too cool, the 78 degree one is best _ I run the 88 in my 4.25, even at 30 degree temps in the summer.

Some modern improvements I will spend money on, a wax type thermostat is one of them.
If it's any comfort, the repro is beautifully cast out of brass and machined, it's not just some pressed production piece of kit form a local auto parts store.

If you want to pressurize the system, you have to have the wax type thermostat, the bellows type is to sensitive to pressure.
RR tried to pressurize the system, but they had problems with the head gasket seeping, someone may correct me about that.
The old style water pump seals may not like it either _ Introcar makes a new water pump with modern seals that will be fine.
The design of your heater matrix looks to be OK, but the old dinner plate style would not work at all.
They expand and contract like an accordion at the best of times from heating and cooling, so under a pressurized system, it would leak for sure _ it's not soldered, just crimped.

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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 639
Registered: 07-2018
Posted on Wednesday, 22 May, 2024 - 15:36:   Edit PostDelete PostView Post/Check IP

Had a look at the Jag and MG stats, they don't accommodate the RR by-pass port.
I don't believe nothing else will work properly.

It's a beasty unto itself, like the distributor cap _ a Chev six one won't work _ if it comes time to get a new one.
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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 160
Registered: 07-2023
Posted on Thursday, 23 May, 2024 - 06:28:   Edit PostDelete PostView Post/Check IP

Thanks Jeff, after asking I felt a bit fat, dumb, and lazy, all of which are true, so started educating myself. Once I realised the bellow holds the sealing plate open I could see where the recirculation fits in.

Good point on matrix, I will have a good look at mine and probably replace with something new as its hidden. I was appalled with the smiths heater in my series 1 LR, bit like pommy windscreen wipers. What's going on in a county so cold and wet? I have had the experience of coolant running across the floor before. I'm the lucky owner of a Mack truck, the only one in history to have a leaking matrix apparently. So much easier to address a new matrix now than after the car is finished.

I found this article which explains history and its progression around thermostats. It to mentions bellow types do not close recirculation very well. Seems however thermostats are a thorn in manufacturers side since water was added to motors.

Just search for the article where drilling bypass holes in the thermostat was the advice.

I couldn't find it, but Normans write up here revealed a few points of interest.

Seems my 72c UE6847 was a 1961 RR service bulletin fitment for year round engine cooling for customers who complained about poor internal heating. It opens at 70-75 and fully at 90 like the rest. It was an attempt to address their previous idea of swapping summer and winter thermostats at service intervals. UE6847 cross references with RE23713 in Normans aricle, and a host of other numbers which I know from reading RR military motor applications and their thermostats. Also where I fond the new old bellow jigger for sale who didn't return the query. I guess they need to update their web site.

There is more in Normans article about thermostat temps, engine wear, fuel atomisation, and his fair point on wax fail closed where as bellow open.


Moss motors have 72c bypass sleeve bellow which can accomodate up to 7psi for $175, but as you say I don't think the sleeve works in the right location.

So I guess no alternatives is a good motivator, 78c $450 delivered, and move on.

My water pump, I'll look into replacing the seals. Thus far it has not been hard or expansive to replace 1957 tech with local 2024 stuff. Its for a non air con'd car however. I need to do more homework on whether I go traditional engine driven or electric. I'd like the air to be in the boot and pumped forward as I think the under dash units are a bit average. Early enquiries leads to a complete new electric system plus a period alternator for less than a second hand OE boot unit with associated motor parts and less refurb, compressor, filter, new hoses, and probably condenser. Easy no brainer really. The crutch is the rear seats fold down in a Countryman to make way for ?. That is if anyone care to show. If i put an aircon of any sort in the boot, one would be looking at, and blocking through access with it.

I think however I just answered my dilemma, air for me, or seat down for others.

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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 161
Registered: 07-2023
Posted on Saturday, 25 May, 2024 - 05:44:   Edit PostDelete PostView Post/Check IP

Jeff, fyi I got a price back on that 78c OE big brass bellow thermostat, around $700AU landed.

Guess it's understandable why manufacturing went the pressed wax type, as an alcohol filled bellow, sizeable chunk of brass, casting, soldering, detailing all cost more in time and materials.

These army boys reckon RR suggested replacing the big brass wax variant every two, no reason why though. Nor have they seen many.

Pic of a wax, working bellow, and broken bellow

What's a bit interesting the way I observe it. The original or the aftermarket from the RR-B suppliers is nothing more than a standard open thermostat. Yes they have a bypass port, but no way of closing it. (check out the image of the aftermarket, I can't seem to copy it)

If I then apply the information about static pressure from the Open Bypass section of the history link. Would this suggest greater-flow through the block would cut off or significantly slow flow from a 90deg positioned port, from the head. Thus causing hot spots or excess heat in the head. Not forgetting the bypass was created to generate then control heat in the head for better fuel atomisation for smooth running performance when a car is cold.

An open thermostat will obviously work as it allows flow of some description. But a car may always run just that bit off, and if the poor ol motor already runs hot from a sediment, then its a good hedge for an expansive future.

I'm thinking if a bellow fails, it fails in the open position. And though its not 100% efficient in closing the bypass, it's a good attempt of that bypass working correctly for 1957 technology. It appears nothing else can be shoehorned, or is made to replace it, except for the offering of the RR-B sellers which I don't believe is genuine nor correct.

I know the wife is not going to like it, but for a part that can't be seen, it's probably not one to be scabby on.
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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 179
Registered: 07-2023
Posted on Tuesday, 04 June, 2024 - 20:18:   Edit PostDelete PostView Post/Check IP

Well that big brass thermostat for $700 landed is like the wax jobbie on the left in the above pic. Not bad really, but.....

I managed to find the boiling points of liquids that fill bellows.

Methanol 65C
Ethanol 78C
Benzene 80c
Isopropyl Alcohol 82C

Then found a company that sells bellows very similar to the OE bellow in height, width, and 12 corrugations over 15, but you have to buy a minimum of 500.

Found a guy on a forum from 2020 also trying to repair his bellow, but can't find the magic balance between volume of liquid V gas expansion to achieve correct opening temperature. Not sure where he got his bellow from but I can't find anyone to sell one or two.

Even found who makes the thermostat for the major RR-B retailers, but they don't sell to the public. I asked a major if the thermostat actually closes the cast bypass port when its in the open position, as the image sure doesn't look like it would. The reply was " from what I read on the forums these are a bypass thermostat as per the original's" Hmmm.

All a bit hard really, dam it.

But then the penny dropped. Do you see what I do? Stare at it for a while.

For under $50AU one can buy a new working bellowed thermostat that opens from a range of temps starting from 65 up to 82c. Admittedly the corrugations are around 9 to 11 instead of 15, but does that matter if the temp is right. Most bellows, or waxed springs for that matter, have a movement range of 7mm. This can be checked while testing the closed/opening to fully open temperature. Then the mounting arms can then be altered and re-attached to suit that movement. The centre pin could also be drilled bigger if needed. The poppet then can then be re-soldered on.

Then all that would be required to really smarten up the thermostat, is a bit of porting to allow better flow when its open. The biggest criticism around bellowed thermostats is that are a restrictive compared to a modern wax.

I have no doubt $700 landed is probably a bargain, however if you have time to spend $50 is worth a try.
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 649
Registered: 07-2018
Posted on Wednesday, 05 June, 2024 - 04:11:   Edit PostDelete PostView Post/Check IP

Here's a photo of the by-pass port from the front, it may be a little smaller then the bellows type, but it does a good enough job of letting the engine warm up, and that's all it has to do.
Perhaps the smaller opening will restrict the flow a bit, causing the engine to warm up faster, and that's what you want.

It will also close off sooner and let more coolant to flow through the rad on hot days.
The whole thing is just more efficient.
The part number on that one is UE30193, and is 88 degrees C.

The down side is that it will fail closed, but given the countless wax type thermostats out there, I really don't think it's an issue.

The red arrow shows the mechanism that slides up and down on the by-pass system.
It's a very precise and beautifully made thing from cast brass.

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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 180
Registered: 07-2023
Posted on Wednesday, 05 June, 2024 - 07:11:   Edit PostDelete PostView Post/Check IP

Thanks Jeff, sincerely.

So it has a guillotine so to speak that closes the cast bypass inlet when the thermostat opens as it gets hot, or pulls down. That's all I asked the retailer.

I must be coming across as a clueless hack who is psychotic over a dam thermostat. But for me it's the heart of the car, not to different to our own. These cars are sold and enjoyed on their smoothness and quiet motors. If it's not running on point because it's too hot, or cold, or not atomising fuel as it should, then it's never going to be what it is, or can be. From their water pumps, slug-less motors, galleries, radiators are all important peripherals that are clear and clean flowing.

I understand wax thermostat came from reducing manufacturing costs as much as better flow performance. Looking at your bypass however, better flow might be marginal, at best. haha. In saying that a spare floating around the trunk is perhaps a must on a long day out.

I will take your advice on 78C for my motor. I have this big beautiful brass thermostat here so think I can give it new life with a bit of love. I have found a 78c bellow.

The bits shaded in silver are what I plan to trim off the existing for improved flow. There is plenty of fat so won't affect structural integrity.

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