no coolant flow, pump ok. ideas?
 

changed the water pump on my 93wrx motor last night (because i was having overheating problems, caused by no coolant flow), but the old pump appears to be ok. a little stiff compared to the new one, but not enought that the belt wouldnt turn it.

the reason i thought the pump had failed was that I'v got no flow through the heater circuit (in my case just a looped hose from the water manifold to the pump). is there anything else that could cause the flow to be cut off? is an airlock actually inside the motor possible?

If the thermostat doesnt open there will be no flow ?

otherwise a huge airlock inside the system, although i doubt it, more keen on the thermostat not opening

deffinately not the thermostat. first thing i changed.

Airlocks are possible, normally caused by head gasket failures :( but you would be losing water as well.
The other option is the radiator is knackered and has collapsed internally, causing a blockage.
Check the pipes when the engine is running, they should feel "hard" and not "squishy", squishy indicates air in the pipes, but give it a little time first.

Tony:)

yeah i have been a bit worried about possible HG, but none of the other symptoms are there, i.e. no bubble in the header, no mayonaise in the water or oil, no smoke/water from the exhaust

the rad seems fine, if i take the top rad hose off and blow into it, i can force water round the system and back out of the radiator (thats with no thermostat in).

my systems a bit more complex than standard, as the engines in the back of a beetle, with a front mounted rad. theres no bleed hose on the rad but i've tried filling it from the rad hose, as well as bleeding the top rad hose with the engine running.
while bleeding it from the rad hose, it gets hot then the pressure seems to force water out of the top rad hose, then i get air (probably when all the waters out, but if i continue to fill up from the header tank while its still running, nothing comes out of the hose.... I'm VERY confused!

anyone know if the head gaskets could have gone without any of the normal symptoms? I've deffinately got no coolant flow and cant work out why!

Just a thought but did you test your new thermostat before fitting it?
Just because its new it may still fail.
Personally I would run the car without the stat in and see if you get flow then.

yep done that, still no flow. even with the thermostat closed, water should piss out of the matrix feed hose if i take it off.... but it isn't.

Sounds like a blockage.

With an engine of that age it possible that there is abuild of debris - especially if the 3yr coolant changes have been neglected or its had a previous HG failure in its lifetime.

In that case then I would still take the stat out and connect a hose to reverse flush the engine to see if you can get it to flow. Try different entry points, IE: top rad hose, bottom rad hose etc etc. you may get it to start flowing if there is a blockage somewhere. Had a similar prob with a mates diesel escort and it did the trick.