OK good to know, thanks! I can cross something off. I am now of the opinion it much be a airlock/bleeding issue. However I don't understand why it would always remain cold if fluid is circulating? I don't understand the logic/workings
We still don't know if your top hose is hot after you've been driving it?
To try to help you understand what's going on here and why we are asking the questions here's a very simple explanation of the water flow in the system.
There is the engine unit itself which has a large diameter top hose going from the cylinder head to the top of the radiator. There is another large diameter hose going from the bottom of the radiator to the water pump (on most of our engines this hose connects to a metal pipe which is plugged into the back of the waterpump casting on the front of the engine.) This is the main coolant circuit. Where the top hose connects to the engine cylinder head there is a cast aluminium "thingy" which the hose is fixed to with a metal clamp. This "thingy" is the thermostat housing inside which is the thermostat itself.
Then we need to consider the heater circuit. Either on the thermostat housing or a separate fixing near it, you will find the smaller diameter heater hose which goes through the bulkhead to the inside of the car where the heater matrix is behind the dashboard (it's just like a wee mini radiator) there is a second small hose coming out of the matrix which is the return pipe and it goes back through the bulkhead and rejoins the engine cooling circuit usually on that metal pipe that runs along the front of the engine. The whole system should be full to the top with water.
So how should it be working? With the coolant/engine cold the thermostat in the thermostat housing should be closed. No circulation, or only very little if an engine has a bleed (which some do to help with air bleeding, but not ours I think?) So no circulation of coolant through the radiator will take place. As the coolant gets hot, 87 degrees C on mine I think? the thermostat will open and water will be propelled up the top hose, through the radiator where it sheds heat, through the bottom hose into the back end of the water pump where it is pushed up through the block back into the cylinder head, collecting heat as it goes, then back through the now open thermostat and round through the radiator again. That it the main circuit.
However we also have the heater circuit, which now a days is usually unrestricted. So whenever the engine is running the water pump will be pumping so water will be going up from the water pump into the cylinder head but, if the coolant/engine is not hot enough the thermostat will not be open so the coolant will circulate through the heater hose, through the matrix, back through the return heater hose to the big radiator bottom hose and back into the back end of the water pump, up through the block and head and back into the top heater hose and so off round the circuit again. When the thermostat opens then water will also circulate through the top hose, radiator and bottom hose but water should be flowing through the heater circuit all the time.
Now what's happening with your car? well, not being there we can't really know but I suspect you must have quite a bit of water in your radiator and engine - otherwise, with the journeys you've been making, you would have been sitting in a big cloud of steam with a ruined engine by now. If you've understood how the thermostat should be working maybe now you realize why we've been asking if your top hose is getting hot. You now know that, if it's working as it should, the thermostat should stop coolant circulating to the radiator until it gets up to around 90 degrees C (as I said I think it's actually 87 on mine) at any rate that's very hot to the human hand to touch. So if you start your engine cold the top hose will feel cold and it should go on feeling cold until, very suddenly, the thermostat opens and the very hot water from the cylinder head rushes up the top hose to the radiator. The time taken will vary from engine to engine and how cold it is but probably around 5 minutes or so.
So you've got your engine running from cold and your hand on that big top hose and its cold - cold - cold - cold - cold - then quite quickly - Oh, I can feel warm - that's getting hotter- Damn that's hot I'll have to take my hand off! If this happens then you've got coolant circulating and that's why you engine hasn't had a melt down.
Let's have a wee think about that smaller diameter top heater hose now. The coolant should be circulating through it all the time the engine is running right? so when the engine is cold if you hold on to it it'll feel cold. then as the engine runs it'll quite slowly get hotter as the engine warms up. The radiator top hose will be cold though because the thermostat is closed . eventually the heater hose will get very hot and you'll now find the top radiator hose is hot too. I suspect you are going to find your top heater hose is never getting hot at all and if so there are two likely reasons. By far the most likely in your situation is that there is a lot of air in the heater circuit. It's possible that the heater matrix could be blocked but if your heater was working before your water pump was renewed my bets would all be on an airlock!
Of course as water should be able to circulate through the heater circuit when the engine/coolant is cold and the thermostat is closed, even if you've got a goodly amount of water in the engine itself, if it can't circulate through the heater that's not ideal! I really think you're going to find this problem will be resolved by bleeding the heater
By the way, of incidental interest and many people don't realize this, people, me included, curse thermostats for failing. In fact I need to do one on my Panda just now because it's not sealing properly and letting water past before it gets hot enough. The thermostat has a hard life. It sits in the cold when the cars not being used then it gets very hot very suddenly but as soon as the colder water from bottom of the radiator comes through it partially closes again until the water gets a bit hotter when it opens up a bit more to let cooler water fro the bottom of the engine come through, then it starts to close again. The result of this is that the water going through the heater stays at a pretty constant nic e and toasty temperature to keep your tootsie warm but the poor old thermostat is constantly on the move, Completely closed to start, then almost fully open with the initial rush of hot engine coolant, then constantly drifting a wee bit open, a wee bit closed , a wee bit more open, a wee bit more closed. It never stops moving whilst the engine is running. Miracle they last as long a sthey do I suppose?
Sorry for the very long post but I hope you now have some idea what's going on with this?
