[b]RADIATOR CAP for FIAT 1089cc and 1221cc engines[/b]

I would like to share some technical knowledge on the RADIATOR CAPS used on FIAT 1100 & 1200 engines, from Engineering principals and personal experience.

The Radiator cap is designed to pressurize the Engine Cooling system, and to increase the boiling point. Some Radiator caps are rated at different pressures, depending on the tension of the spring and internal diameter of the sealing face. There are also other technical features on Radiator caps which include a return valve, when a resevoir is fitted.

It is very important to USE THE CORRECT "PRESSURE RATED" RADIATOR CAP for your FIAT 1089cc or 1221cc engine.

If you fit a Radiator cap with a higher rated pressure, it is possible for your CYLINDER HEAD to START LEAKING, in other words you will be OVER PRESSURISING YOUR COOLING SYSTEM, and the easiest path for the water to escape will be in between the cylinder head, engine block and head gasket.

This happened to me many years ago, when I bought another FIAT 1100D. When the engine was warm, small amounts of water droplets would start to come out on the sides of the engine block and cylinder head. I thought that the HEAD GASKET WAS BLOWN, so I removed the cylinder head. The cylinder head was OK, I checked it with a straight edge, and even sent it to skim slightly. When I installed the cylinder head again with new head gasket, the same thing happended again. I could not understand what was going on. I then looked at the Radiator cap and felt the spring tension, and realized that the spring tension was harder than the other Radiator cap from the other FIAT 1100D. I solved the problem.

Lets check that we are using the correct Pressure Rated Radiator cap for your engine.

Hi Luigino

Apologies for being rather quiet recently - been immersed in Citroen DS stuff... This is the wrong place to say it, but the DS is something rather special and once I turn my attention to it, it is quite hard to switch out again... (I think anyway!)

That info is very interesting. I haven't had the problem on the 1100 (but will check the radiator cap - does it have numbers on it?) but I had exactly the problem you mention on the engine of my Land Rover Series One... It's since had the engine overhauled and needs to be rewired so is off the road, so good time to check the cap....

Am taking my 1100 in to a different mechanic next week that specialises in Alfas and performance cars... I want them to have a look at a couple of things that my previous mechanic always seemed to "forget"... Took it for a nice drive yesterday, going like a dream!

Keep the technical info coming...!

All the best, John.

There are always numbers on RADIATOR caps, which refer to the technical details about the cap.

As an example, a part number can be T3-10, or TG3-10, T3-4, depending on the manufacturer. The "TG" can refer to the double internal seals, and the 3-10 the pressure rating in PSI. (the numbers refer to the pressure rating, as in this case 3 to 10 psi)

14 PSI is about 100KPA

I think that my RADIATOR CAP is rated at 50KPA., that is 7PSI rating. (will check up again)

I checked in some old catalogues on the internet, regarding the FIAT 1100 and 1200 RADIATOR caps, Some are rated at

1) 25 KPA (SAE range 3-5 psi), Safety Release Cap rated at 4 psi, and
2) 50 KPA (SAE range 6-8psi), Safety Release Cap rated at 7psi.

I seem to remember that I once used a RADIATOR CAP with 25KPA rating, but the pressure was too weak, and my engine began to vaporise water more regularly. The 50KPA rating is better.

It is also important to check the vertical distance of the RADIATOR CAP, from top to bottom of neck.

Regards Luigino

Luigino,
You are the "fountain of knowledge"!
I am going to check the radiator cap soon...when my mechanic puts the car back together again.
I'm not sure if you had seen in another post,on the Italian side,that I have a question with my motor.
The pistons that are in the block right now,a 1200 (103g005 ) are flat,yet I have been seeing pistons on the web - 72.4 , because I now need oversized pistons , are domed...
Any ideas about that?I am trying to finish the rebuild on the engine,but I definitely want to do it right.
Any help or ideas you might have would be greatly appreciated...the car is in Tucson now,but I live in New York,and I would like to driving around the car a bit before the winter sets in.
Any photos of your car you can post on the site?It is always nice to see othe cars out there.
Thanks,
michael

Hello Michael

1) the pistons of all 1221cc engines have a 72mm bore
2) there are 3 different types of 1221cc engines, 103G:000; 103G:004 & 103G:005
3) all the pistons are flat. In some cases I have seen some slightly dome pistons, but those are the special pistons for higher compression.
4) the Fiat 1300, from 1961 has also the same 72mm bore, but those pistons are dome in shape (at the top)
5) the compression length of the 1221cc piston is 46mm (if I remember correctly), this measurement is the distance from the centre of the gudgeon pin to the flat top of the piston.
6) gudgeon pin diameter = 22mm

Before you rebore your engine, I suggest that you get the machine shop to measure the cylinder bore just below the top ridge where the most wear is. Once they have measured the wear, they can determine how mush they can rebore. Then you should try and see if you can get the particular piston size that the machine shop recommended. If not, then try go for a larger size piston. The largest size available as far as I know is 60 thou which is about 73,524mm.

The same applies for your crankshaft, if you need to have it ground. Measure first, then find the suitable size bearings shells.

Best of luck, if you need any other info, please ask, I will try and help where I can.

Kind Regards
Luigino.