Overheating Troubles

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Hey all,

(my coolant level was half way between the min and max marks when the
engine was cold when i checked 2 days ago)

I was driving along today and stopped at a store real quick to pick
something up, but when I came back out I noticed bright green coolant
flowing out in a small river from under my car down the parking lot. I
didn't shit my pants quite yet because I thought it might be from someone
elses car but I popped the hood and sure enough it was coming out from
around the expansion tank cap. The temperature gauge was just over 1/3 the
way from the red led at the middle to the maximum temp, but the overheat
light was NOT on. I left the engine off to cool down for 3 or 4 minutes.

I drove the car a short distance then pulled over to look at it again. The
radiator hoses were fine, not kinked/collasped/broken, the v-belts were
fine, no strange noises from the water pump. The radiator was hot. The
only thing wrong was that the radiator fan wasn't on (!). I sat there for
10 minutes to let it cool to the half way mark and think. I drove home
with the A/C on and the blower on so the high speed fan would run (I
checked to make sure it did), and it ran on the hot side of the half way
mark just a little all the way home.

When I got back, I opened up Bentley to try to figure out what to do next.
I think I was able to rule out bad thermostat (at least stuck closed), bad
water pump, clogged heater core, bad hoses and clogged radiator... at
least as the primary cause. I let the car cool completely then drove it
for 25 minutes with the A/C fan trick. The car stayed cool at the half way
mark. I was convinced the cooling fan was the problem. I pulled the metal
cased relay by the battery and cleaned the (terribly corroded) contacts,
and did the same for the 2 two conductor connectors near it. I took the
connector off the fan too, and it looked fine. I couldn't get to the fan
thermoswitch or its wiring.

I then ran the car without the fan trick for about 10 minutes until it got
up to a little above half way. Then i turned the a/c fan on for 1 minute
and then off again. The electric fan was on, but at slow speed. About 20
seconds after I turned the engine off then, the fan went off, even though
the engine was really hot. This can't be normal, is it?

I'm rambling... to the point: I'm guessing this is one of these 3 things:

1) Bad thermoswitch

2) Thermoswitch sensor element covered in goo, insulating switch from high
   temp coolant and making it "see" a lower temperature

3) Bad or corroded fan wiring or bad grounds

Anyone have any idea what would cause this all of the sudden? The car has
been running at 7/8ths of half way mark to half way mark for as long as
I've had it.

I checked the oil and coolant for coolant and oil (respectively), because
I've had to have a number of head gaskets replaced over the years in
various GM and Japanese automobiles and its never fun. Fortunately it
looks like the oil is oily and the coolant is green.

Oh, one more thing -- would it help at all to drain the coolant and reload
it with new phosphate free coolant and water? Would that improve the
cooling effectiveness at all or is it just preventative maintainance? I
plan on doing this anyway, but I'd probably do it asap if i knew it was
going to help the problem.

Yak yak yak...

-Toby

--
'87 Flash Silver Metallic Scirocco 16V

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