Thermostat water pipes

[DanielC]

The L-18 engine in one of my 521 trucks, Dragon is running warm.  There is not a connection from the bottom of the thermostat housing to the pipe that connects from the intake manifold to the water inlet by the alternator.

another picture, same engine, from the front.

 

 

This is the thermostat housing on the L-20-B engine in Ratsun, and this engine tends to run cool, and this is a L-20-b engine with a stock 521 L-16 radiator.  My finger is pointing to the hose going to the bottom of the thermostat housing.  The other end of this hose connects to a "Y" in the waterpipe from the intake manifold.

 

Looking at another L-16, or L-18 engine, there are these pipes.

 

So my question is this.  How important, or how much does having the water pipe removing water from the bottom of the thermostat housing to keeping the engine at the correct temperature?   Dragon, without this pipe runs hot.  Ratsun, with this pipe does not run hot.

 

 

 

 

 

 

 

 

Edited July 14, 2020 by DanielC

[datzenmike]

The by pass circulates coolant from the block and head past the thermostat so that it can sample it's temperature.The thermostat responds instantly to engine core temperatures. It's piped directly back into the block so that it doesn't slow the warm up. Without it, the water around the thermostat is stagnant and warms mostly by convection through the aluminum more than the water.  

 

521 and 510 didn't have the by pass hose connections. They relied on a jiggle valve' in the thermostat which basically is a small leak so coolant does circulate past the thermostat but into the rad. This displaces cold water into the block. The jiggle valve can't be too big or the engine doesn't warm up, too small and the thermostat doesn't soon enough. It works but not as well as a dedicated by pass.