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Discussion Starter · #1 ·
My st170 seems to be getting through about an expansion bottle full of coolant every 2 weeks.

There is no mayo in the oil filler cap, no oil in the expansion bottle and no white smoke/steam out the exhaust when warmed up so i think head gasket is ok.

i noticed a damp patch on the drive after the car had been moved, but where could it be leaking from? i will check hose joints, but as i am new to st's, are they prone to anything in particular to leak?

any advice?
 

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Had a similar problem with mine back in 2006 (53 reg 30,000 miles at the time) after a few trips to Ford it was diagnosed as the thermostat seal/gasket. Had this replaced under warranty but still leaking, not as much though. Took it back and they then replaced the complete thermostat housing, which solved the problem completely. Apparently the seal is rubber and over time it perishes. Not saying it's definitely the problem with yours but it sounds like it could be. If it is that, it's not such an expensive fix...

It's under the cover I've marked with a red dot, down where I've put the red arrow. If it's leaking there will be a pink/red stain from the coolant around the part that looks like a plug...

 

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My ST170 had the same problem and it was the thermostat housing. It is very common. Mine leaked around the blanking plug. Some silicon applied and allowed to dry before fillling did the trick.
A new thermostat housing is about £50-60 by the way.
 

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Discussion Starter · #4 ·
mine is indeed leaking from that very spot. i traced down the leak earlier before my membership on here was updated.

i thought i could remove the thermostat housing and replace the seals and reasemble with a new thermostat while i'm at it. i also thought i could put a smear of sealant around the seal too while i was at it for good measure.

that sound ok?

is there anywhere i can get an exploded diagram with part numbers from? is there a haynes manual for the st170 for some bedtime reading.
 

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Its not normally the main seal to the head, it is generally the small seal that fits on the blanking plug. That does not come as a spare aprt apparently. Silicon worked fine on mine. The key was to let it go off properly befopre refilling and running up.
 
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