After some distractions, I finally got a chance to look some more at
our Impreza's overheating problem. Initially, I thought the problem was
electrical as none of the fans come on but it is something different, I
think now:

The fans don't come on but can get them to come on by putting a
variable resistor on the thermosensor - so the fans not coming on is
not due to any of the relays, wires, bad fans, etc. The ECU clearly
works ok as well.

Replaced the thermosensor - still the same problem. Measuring across
the thermosensor at temperature I get 290 ohm, from the looks of it.
Using a potentiometer, the fans come on at around 250 ohms.

So I am wondering if the coolant is circulating. I don't dare run the
car too long, but the bottom hose does not seem to get very warm. Took
the thermostat out and tested it in a pan of boiling water - it works.

I've tried burping the system by rolling the front on ramps and revving
it while filling the radiator. When that didn't help, I drained the
whole system, filled the engine first (using the top hose and a long
funnel), then the radiator -- still no joy.
I was half thinking of finding a steep incline and trying to burp the
system but that just seems extreme.
Is there a better way to burp the system?

How can I tell whether the waterpump is bad? I replaced that thing last
year when I did the timing belt. Usually don't waterpumps start leaking
when they go bad?

The car runs really well antifreeze does come out the cap eventually
when it overheats.

Tia
Remco

Remco wrote:

You could have the radiator flow tested I think.

I dunno

Carl


--
to reply, change ( .not) to ( .net)

With the radiator cap off do you see any circulation when the
thermostat opens? Is the bottom hose collapsing? If not to those two
questions then maybe the waterpump shaft is turning but, the impeller
has come loose.

Edward Hayes wrote:
I see the coolant rise when I revv the engine. Would that constitute
circulation?

I'd be mad if it was the waterpump because I replaced that thing about
a year ago.

Remco wrote:
Just by way of an update, this particular problem ended up being the
radiator cap and the radiator:

The radiator cap did not allow for pressure to build up and air to get
into the system. When I replaced it, I found a weep hole in the top of
the radiator.