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Discussion Starter #1
It seems that the 45mm screw-in thermostats have become near "unobtainium". 40mm versions are available, but the larger ones don't seem to be readily available any more.

Has anyone converted (without total manifold replacement) to newer drop-in style thermostats??

(I'm eyeing a couple of newer fuel injected manifolds as donors for the thermostat holder...)
 

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Hi Bruce. What is the inside diameter of each? Looks like it could be close to the same.

What is your thinking about converting. Why, what is down side of using a 40 mm version?? How? Are you going to do some welding or find an inline thermostat?
 

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Discussion Starter #3
Hi Bruce. What is the inside diameter of each? Looks like it could be close to the same.

What is your thinking about converting. Why, what is down side of using a 40 mm version?? How? Are you going to do some welding or find an inline thermostat?
I'd have to measure each (and the one in the manifold is not going to nicely come out) - but the ID of the 40mm is MUCH smaller than the 45mm.

NOTE: - I'm NOT thinking to convert to a 40mm screw-in. Too small for the coolant flow I'd like! ...and just as troublesome. I just happened to have one from an ordering mistake :)

I'd love to use a drop-in style as found on some fuel injected models later. My initial thought is to place a holder in the hose about where the old one exists. Using hose & clamps - I'm not going to weld aluminum alloy with my skillset.
 

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I'd love to use a drop-in style as found on some fuel injected models later. My initial thought is to place a holder in the hose about where the old one exists. Using hose & clamps - I'm not going to weld aluminum alloy with my skillset.
Hmm. The only practical way I can think of to use a drop-in thermostat is to use a later manifold. You will need to spend a few hundred bucks to find a good, used manifold, but it will be a clean solution. These use a bypass hose - so you'll need a different water pump as well - but the bypass hose offers the benefit of a faster warm-up time.

The alternative you mentioned - "place a thermostat in the hose" - might be implemented with something like a BMW 2002 thermostat (see picture below). I have no idea if the diameter of the bungs on the 2002 'stat would fit the Alfa hose. Admittedly, this approach does not use a drop-in thermostat, but it does replace the screw-in 'stat.

 

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Discussion Starter #5 (Edited)
Hmm. The only practical way I can think of to use a drop-in thermostat is to use a later manifold. You will need to spend a few hundred bucks to find a good, used manifold, but it will be a clean solution. These use a bypass hose - so you'll need a different water pump as well - but the bypass hose offers the benefit of a faster warm-up time.
The manifold that is currently in use was the only style that supports the underside throttle linkage with the bell crank and rods... which is why I used it. That thermostat is a problem, though. Between that issue and possible faster warm-up, maybe I should have re-engineered the throttle linkage for the overhead cable style...

Plan A is still to extract the old screw-in thermostat and find a replacement (found some - in Australia… a month's shipping time & $$$) - but I fear they might not be available at all next time.

Something like that BMW thermostat was what I was considering - both hose sizes and actuation temperature could be tricky to match up... But worth a look, maybe.
 

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Discussion Starter #6
A 1976 BMW 2002 in-line thermostat is only $15, which is cheap enough to pick one up to fool around with. I see an 80 degree version is available, which seems close enough.

Wish I could measure one...
 

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Discussion Starter #7 (Edited)

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The manifold that is currently in use was the only style that supports the underside throttle linkage with the bell crank and rods.emperature could be tricky to match up... But worth a look, maybe.
No, the screw-in thermostat manifold is not the only style that supports the underside throttle linkage. Later carburetor manifolds had drop-in thermostats, but used the same type of linkage. That's what I meant in post #4 when I wrote: "The only practical way I can think of to use a drop-in thermostat is to use a later manifold."

Here's the carb conversion kit that Centerline sells; I know you don't need all these parts, but check out the type of manifold they supply:

 

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Hi Bruce. What is the inside diameter of each? Looks like it could be close to the same.

What is your thinking about converting. Why, what is down side of using a 40 mm version?? How? Are you going to do some welding or find an inline thermostat?
Hey Bruce. You want us to share info with you right? So when you get time please measure both the IDs and share with us here on this Alfa BB. Someone other than me might also be interested.

Btw. I'm with Jay's suggestion. Get a carb manifold with drop in thermo. This type started with 1750. The screw in type was used on 1600 and 1300 engines. You don't say but I'm guessing you have 2 ltr 76 spider converted to carbs.

Thanks

Ken
 

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Classic Alfa in the UK keep an extensive store of second-hand parts, including intake manifolds (both types). I purchased a drop-in Weber manifold from them a few years ago. I thought the purchase price was very reasonable. Keep in mind that the European 4 cylinder Alfa used carbs for a much longer time than the US version Alfas.
 

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Discussion Starter #11 (Edited)
Hey Bruce. You want us to share info with you right? So when you get time please measure both the IDs and share with us here on this Alfa BB. Someone other than me might also be interested.

Btw. I'm with Jay's suggestion. Get a carb manifold with drop in thermo. This type started with 1750. The screw in type was used on 1600 and 1300 engines. You don't say but I'm guessing you have 2 ltr 76 spider converted to carbs.

Thanks

Ken
I will post those measurements, promise! But be patient... :) That old 45mm thermostat is REALLY stuck in place - and may not come out in one piece. Last night I didn't even get time to measure the loose parts (or the rubber hose ID - it necks down from 45mm to …?)


All - I hear you about manifold replacement, and if I do it, that approach has great benefit for my grandkids when they inherit the car (long after I'm dead :) ) - fewer non-Alfa parts to wonder about.


I see a note about using a cooler-actuating thermostat (70 C) on a twin-spark to get more HP, and I wonder what folks have found on a single spark dome head 2LTR?? Any benefit to using a cooler thermostat? (I only run my Spider in warm weather anyhow!)
 

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That old 45mm thermostat is REALLY stuck in place - and may not come out in one piece.
This sounds like one of those "up to your a** in alligators / drain the swamp" situations. Why again did you want to change the thermostat?

Those screw-in thermostats can get permanently corroded into the manifold. Another reason to just get a 1750-style Weber manifold, the drop-in thermostat that fits it and meets your temperature requirements, and not bother trying to remove the old screw-in 'stat.

Is your car a 2 liter? And if so, does it still have a 3-port water pump with the bypass port blocked off? If so, you will also need the bypass hose for a carbureted car. But if it has a 2-port water pump, you'll either have to block the bypass port under the thermostat on your new 1750 manifold (not my recommendation), or install a 3-port water pump & bypass hose (better solution, but more work).
 

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In RJ's thread about putting the Montreal engine in the spider, he had pictures there of using motorcycle thermostat housings just in the coolant hoses. I think he said they were from a Yamaha R1, looked like a reasonable solution.

Found it, if I do this right, this will be a link to the post. Otherwise it is post 184 on page 13.

Cheers,
 

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Discussion Starter #14
[…] Why again did you want to change the thermostat?
Classic thermostat failure symptoms - slow to heat up, followed by getting a bit too hot on warm days (probably 1/2 open and not moving).

Those screw-in thermostats can get permanently corroded into the manifold. Another reason to just get a 1750-style Weber manifold, the drop-in thermostat that fits it and meets your temperature requirements, and not bother trying to remove the old screw-in 'stat.

Is your car a 2 liter? And if so, does it still have a 3-port water pump with the bypass port blocked off? If so, you will also need the bypass hose for a carbureted car. But if it has a 2-port water pump, you'll either have to block the bypass port under the thermostat on your new 1750 manifold (not my recommendation), or install a 3-port water pump & bypass hose (better solution, but more work).
I need to see ground truth under the hood as to which water pump I am currently using - but I have 2 good 3-port pumps and maybe a 2-port installed currently. The photo is one of my 3-port pumps. The second photo is the other intake manifold - without mounting for a bell crank - but with a drop-in thermostat housing.


If I fracture the current manifold trying to get the old thermostat out, I'll definitely change the manifold.
 

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Drop in manifold needs to be Euro style that supported carbs. I've never had a screw in type that didn't come out that hard. It's usually best to remove from engine if too difficult. Brass threads and aluminum usually do not seize.. they don't need to be torqued when put in, just firmly snug. It has nowhere to go and it is surrounded by hose and clamps.
Cheers, Jon
 

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. The second photo is the other intake manifold - without mounting for a bell crank - but with a drop-in thermostat housing.
That's a Spica manifold. Adapters are required to mate Webers to a Spica manifold, and the method for sealing the carb throats to the adapters can be trouble-prone. I wouldn't recommend trying to use this.
 

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I have the BMW thermostat. It is 32mm on each port. That is 1 1/4 in. Having a big bypass port is odd, but not impossible. I used a 1 in. hose and stretched it over working the parts on a bench. Whenever I remove it to access parts of the car, I leave this hose on the part. You could use a reducer pipe, but I didn't want two more hose clamps.
 

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Discussion Starter #18
Here's a couple of measurements - the 40mm screw-in style, and a later model drop in thermostat. I happen to have both...
The tops of the threads on the brass screw-in are just a bit under 39mm, and the diameter of the drop in is about 54mm

The 45mm thermostat is still in place - a 45mm socket arrives today.
 

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Discussion Starter #19
That's a Spica manifold. Adapters are required to mate Webers to a Spica manifold, and the method for sealing the carb throats to the adapters can be trouble-prone. I wouldn't recommend trying to use this.
That one came with the engine - and I didn't like the look of the adapters. I don't have it anymore.
I'd have to locate a manifold for a decent price to swap. The one that's on there works fine except for the thermostat (now).
 

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Discussion Starter #20
It's done!

Two things - First, how I got the old thermostat out - Picture #1


Second, @kengta - you were right!! The 41mm thermostat has exactly the same thread as the 45mm. Further, although the 45mm has seemingly slightly larger inlet cutouts, the thermal slug is SMALLER in diameter - making it most likely exactly the same coolant flow...
 

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