scarmonasven

I have problems with the cooling system and I don't know what it could be. The temperature gauge stays at operating temperature throughout my drives, but when I check the expansion tank the coolant starts to pour out from the overflow hole. The top radiator hose is always hot and the bottom hose is cold. The coolant is old and needs to be changed.

John535is

When the bottom hose is cold it generally means the thermostat is not opening.
Interesting the car is not overheating and the gauge is not going over the centre.
Does the heater work?

scarmonasven

The heat works very well, someone suggested that it might be a bad water pump or that someone mixed two types of coolant.

John535is

Yes it could still be the water pump or just some gunk causing a partial blockage making the pump perform badly. I was expecting you to say the heater did not work which combined with the lower hose being cold would point to the thermostat not opening. Since you have heat you therefore have 'some' circulation. The information you got about mixed coolants has been known to result in sludge in the coolant again causing a partial blockage. Since the water pump is a pain to replace I would start with a good coolant flush using a chemical flush agent. You can buy a purpose pressure cleaning set up or just be prepared this is going to take some time and lots of mess to do this by repeated flushing.

Everyone will have an idea on this, my way is: run the engine till the water is a bit warm, but I don't like the engine to be hot as you will be removing the cooling medium (water), turn off, dump the existing coolant. Fill with water, repeat, fill with water and radiator flush, now run till hot and have the heater on so you are now flushing through the heater core as well. (Instructions are normally on the bottle of radiator flush). Leave it to cool a little, dump water, repeat with clean water till hot, let cool, dump, fill again. Now hopefully if you are catching the fluid you will notice the early flush had some nasty crap in it, the flush with the radiator chemical will probably be a strange colour, the next flush should be pretty clear. If you are still getting crap or chemical coming out, repeat until its pretty clear. Refill and bleed off the air from the heater hose and the top bleeder.

During the process hopefully you will get some gunk out and start to feel heat on the lower hose under the thermostat. You should also consider how you are going to dump all this water. There is a little bleed screw on the bottom of the radiator that usually breaks if it hasn't been used. Check this first and maybe purchase a new one prior. I also usually just undo the lower radiator hose and let it dump out, that way any gunk has a better chance of getting out than through the bleed screw hole. Now if you are still not getting any heat on the bottom hose the pump is you focus. They are not expensive to buy, but a bit of a pain to install.