External Oil Thermostat Hose Diameters...

Hello, I've recently bought an Oil thermostat from Mishimoto.

But I could not get my head about the diameter of flow. My Engine used to have Water/Oil Heat Exchanger and the body of the exchanger has two ports. Engine Oil Inlet is 15mm diameter. And Engine Oil Return line is 14mm in diameter. I've checked the Oil Thermostat has AN10 fittings and 12mm inside diameter of the ports. Does it effect my oil flow?

Also I've found same engine block with old cars used to have external oil thermostat with external Oil radiator. Oil exit from the Engine Block is 12mm

Oil Thermostat inside passages is 13.5mm

Oil Cooler Radiator Hoses are 10mm inside...

I am totally lost in here. Can you give me a guide here a little bit... I live in Turkey And I cannot find AN fittings and Hoses easily. I have to order them. What do you think about the differences of diameters.

-10AN is typical for oil cooler setup or oil filter relocation. Never had any problem using that size.

What engine is it?

A relatively small N/A engine is going to have a much lower flow than a large turbo'ed engine with oil squirters, etc.

MY engine is 1910cc - 4Cylinder, HighPressure Turbo Diesel with under piston oil squirters. Thats why I'm afraid about the oil line resistance. My hydraulic guy told me that small diameter changes in short distance does not count. It does not effect the flow. But they work with 250Bars of Pressure in their daily works. This car is 4-8 bars Oil Pressure. I'm really getting crazy about the engine oil.

I could feed 14mm with AN fittings to the Thermostat, But I hope, inside of the Thermostat body does not make resistance to flow.