Quote:
Originally Posted by bradsm87
I've done some reading and don't believe that a spring can be made to reliably change spring rate based on temperature. I think the way it works is based on oil pressure and viscosity, which also happens to vary consistently based on temperature. When the oil is cold, it is more viscous and oil pressure is higher. This overcomes the spring pressure and opens the closed plunger, bypassing a lot of the oil from going through the oil cooler. Once it gets to a certain temp, the oil is less viscous and oil pressure is lower, allowing the spring to close the bypass plunger and all oil flows through the oil cooler. This kit would have a stiffer spring, keeping the plunger closed above 90C. Here is a pic from one of the N54 technical training documents:
https://drive.google.com/file/d/0Bwk...ew?usp=sharing |
Sorry yeah you're right. It's unlikely anything to do with the actual temperature on the spring but by the strength of the spring vs oil pressure.
Prior to installing it I didn't actually compare the stock spring vs the upgraded spring in terms of strength but the design is different compared to the stock thermostat valve.
In the stock thermostat, the valve is actually significantly wider ~15mm and it sits over the spring that is inserted first. There is no protruding guide rod. Increased oil pressure would cause the valve to compress the spring and be pushed inwards away from the cover.
In the AD thermostat, the valve looks more similar to the BMS one with a smaller valve thickness ~5-6mm with a protruding guide rod and the spring is inserted after the valve. This means that with the increased oil pressure, the valve compresses the spring and is pushed outwards towards the cover.
I don't know enough about the flow directions of the oil thermostat housing to say specifically how it works other than that from preliminary testing, it does exactly what it is is designed to do. Opens at about 90ºC and keeps temps lower than the stock thermostat during normal driving.