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roy4matra
YaBB God
Posts: 1213
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« Reply #1 on: August 02, 2016, 09:04:47 am » |
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When filling coolant, after installing stainless steel coolant pipes some years ago, I wondered about the configuration of the small hoses entering the expansion tank. The small hose from the thermostat housing connected to the top of the expansion tank, while the small hose from the top of the radiator connected to the bottom of the expansion tank. Now, after replacing the water pump for the second time (see other posts about that) I again wonder why the small hoses are connected as they are. To me it would make sense if the hose from the top of the radiator would connect to the top of the expansion tank, thus allowing air in the radiator to be vented out of the system. Connecting it to the bottom of the tank makes coolant flow back into the pipe, and block air from escaping the radiator. Therefore, are there any of you who have the hoses connected as I suspect is the correct way? Namely Thermostat housing to the bottom of the expansion tank and top Radiator hose to the top of the expansion tank? Hello Jon, Both these hoses are air vent or degassing hoses, the one from the thermostat housing is venting air from the engine just as the other is the radiator venting hose. The real problem I suspect is that the header tank was taken from something else, and doesn't have the connections just where they are really required in this application. The hose from the thermostat housing is tiny compared to the connection on the header tank, showing it wasn't designed for it, so they had to use two different size hoses and join them with a reducer (which was plastic and eventually broke as it became brittle with age and heat) and you ended up losing coolant if you didn't spot it, or replace it before it cracked. Once the system is originally bled of air, the system should remain air free unless you get a leak. However, the most likely place to introduce some air into the system would be the engine or water pump and if this is bled out straight away (from the thermostat housing) it won't even reach the radiator to need bleeding from there. So I suspect the engine degassing has priority and hence the reason that hose goes to the higher connection. Another reason may be that the radiator hose connection on the header tank is higher than on the radiator even when it is connected at the bottom, whilst the engine degassing hose if it was connected at the lower connection would be almost the same level and wouldn't provide as much upward flow. With the hoses connected as they did at the factory, there are reasonable differences in height for upward flow on both degassing hoses. Roy
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« Last Edit: August 02, 2016, 09:07:25 am by roy4matra »
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roy4matra
YaBB God
Posts: 1213
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« Reply #10 on: February 08, 2019, 01:47:49 pm » |
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I am replacing my header tank with an aluminium one, that only has a connection at the bottom, and one at the top , above coolant level. (And one for overflow at the cap). From what I hane read here it seems that it would be ok to simply connect both the radiator venting line and the one from the thermostat ,to the upper one by means of a t-piece ?
No, you should leave the radiator bleed hose at the bottom of the header tank where it is under the coolant level. If the fluid level dropped owing to a leak you want the radiator to remain free of air, so having it under the fluid level at the header tank would do this, until the tank was completely empty. If it was connected at the top where there is always air, it could get air back into the top of the radiator as the level dropped. The extra height of the connection at the bottom of the coolant tank compared to the top of the radiator will always allow a small flow of any air bubbles that appear at the top of the radiator to vent back to the header tank. Don't forget all this system is under pressure at normal running. If you were going to use a tee-piece for the two to the upper connection, what were you going to do with the bottom connection? Just cap it off? Why? It is better to leave the hoses connected the way they have always been, as Herman says, which we know works fine. Roy
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« Last Edit: February 08, 2019, 01:50:17 pm by roy4matra »
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