Coolant system not pressurising.

[Welsh Dan]

Over the last week or so my heaters have gone poo, and the temperature indicator barely gets above the blue mark. I've just come home from a 15 mile drive and the coolant system was not pressurised, but I can't see any obvious leaks.

I'll get a new header tank cap tomorrow, but where else should I be looking if I cant find any leaks from the hoses/waterpump/rad?

[Adam]

Hmmm, weird.
As if it aint pressurised then the system should be overheating. Whereas you seem to be getting the opposite effect.

[Welsh Dan]

Coolant is slowly going somewhere, i forgot to add.

[Adam]

Sounds like pressure cant build because its leaking through a split in a pipe or somewhere.

[Welsh Dan]

This'll be fun to find lol.

edit: hopefully it'll just be the cap, and its just evaporative loss.

[Stuart]

how skanky and cracked is the header tank?

also maybe try to swap your thermostat.

[Welsh Dan]

The header tank is pretty skanky in terms of residue, but I havent seen any cracks. I'll have a look tonight.

[Stuart]

I'd replace it as a matter of course, they should only be ?20 or so.

the cracks might not be obvious as they appear as lines in the tank.
They arent UV stable and over the years start to yellow and crack... or if the tank is on display to the sun all the time they fail in 2 years :s

[Welsh Dan]

The tank has gone yellow lol. My local dealer+preferred motor factors don't have the tank, so I'll try a breakers/other factor on friday when im off.

[Welsh Dan]

I think it might be the radiator, had a look when I got home tonight and I can see residue that can only really have come from a coolant leak, and I know the back of the rad was clean when we did the engine swap.

[Welsh Dan]

Well after a new coolant header cap and a bottle of radweld is marginally better, but not right.

Here's an oddity: I went for a 15 minute drive around, keeping the revs low to get the coolant warm, pull up at home on the driveway, open the bonnet. The hose from the thermostat to the radiator is boiling hot, the bottom hose from the rad is absolutely stone cold. 10 minutes later with the engine idling the whole time that hose is still stone cold. I take the coolant cap off and then squeeze the thermostat-rad hose several times and the rad, bottom hose and overflow hose all get very warm very fast.

Water pump issues possibly?

I won't get time until sunday to do any big jobs, but I'm thinking of flushing the whole cooling system, replacing the header tank, thermostat, water pump and coolant, and possibly replacing the radiator at this point :(.

[Adam]

Waterpumps usually gurgle/grind when there fooked, and leak due to play in the bearing.
Unless the impellors just sheared off or something.