Rubbish plastic thermostats

[SD1too]

Originally Posted by Dorset Bob

You state that the 'O' rings are the same on both types, so why do they leak on the plastic ones and not the metal?

Hello Bob,

Thank you for asking. I have spent a lot of time carrying out tests on my own engine as well as taking into account evidence from other forum members. It was actually Minimutly who had the idea which led to the breakthrough but I did the donkey work. In order to answer your question properly Bob, I will first explain how the plastic pipe system should work.

The plastic components are obviously lightweight; that was the reason for MGR choosing that material. Minimutly suggested that they can move in service (22.12.15, post no. 17). If the large hose to the thermostat housing is grasped and tugged you might see this for yourself. This movement pivots about the 'O' ring at the base of the thermostat housing which is where the leak occurs as the ring becomes flattened through friction.

In RAVE (26-3-17) it is stated: "Secure coolant pipe with clips". This is, of course, referring to the serrated ("Herbie") clips mounted in channels on the straight pipe. The purpose of these clips was not considered by anyone, including myself, until Minimutly had his idea. So what exactly do they do?

In order to fit the plastic parts to the engine the straight pipe must be able to slide to the right into the thermostat housing such that the other end can be inserted into the water pump. Once this has been done, there is nothing to stop the straight pipe moving left and right when the engine is running. This movement causes friction to the straight pipe's 'O' rings and also rocks the thermostat housing in its mounting causing the same to happen to the 'O' ring at its base. These movements are small but continuous and the long term effect is easy to imagine.

The serrated ("herbie") clips on the straight pipe are there to prevent this movement. Each sits in a channel somewhat wider than the clip's dimension. This enables them to be moved from side to side. When they are fully inwards the pipe is set for assembly. When they are fully outwards, the pipe is prevented from sliding between the thermostat housing and water pump. It is securely fixed in position and the serrated jaws are adjusted to keep it there. This is the purpose of the clips. It is confirmed by RAVE (26-3-17) which states: "Secure coolant pipe with clips". If this procedure is followed, the 'O' rings on the plastic components will not leak.

The reason that people mistakenly believe that the thermostat housing welded seam splits is because pressurised coolant sprays upwards from the flattened 'O' ring and deposits itself around this seam. I have proved this by refitting the following housing to my engine with only a new 'O' ring and the leak was cured! No-one else has had the conviction to do this.



Thanks for your patience so far Bob. Now I'll come to the crux of your question. The reason why the same 'O' rings on Kaiser's metal components don't leak is because the cast aluminium is inherently heavier and much more rigid than the plastic and so successfully resists any movement. The 'O' rings on his parts therefore don't suffer any friction. It should be noted that one disadvantage of Kaiser's system is that it uses an 80 degrees thermostat so the engine will run about 10 degrees too cool. The parts are also expensive to buy when all that is necessary is a set of 'O' rings and an adjustment of the serrated clips.

Sorry that this is such a long reply. I know that some aspects of it have been challenged on theoretical grounds, but the proof of the pudding is in the eating and my engine has been leak-free for several years now so I think that speaks for itself.

Simon