I gave my 2.5 a complete radiator flush (removed both large & small rad) and reverse flushed. Also replaced main stat but cannot undo 1 of the bolts on the small (aux) stat, the lower bolt is a 10mm & came off easily but the top bolt which bizarrely is 11mm (is this normal) will not budge. I've tried with a socket & wrench & with a spanner and it won't turn. Of course I could use a larger wrench but I'm worried that this would shear the bolt off. Hope the previous owner hasn't put locktite on it or something!

Thinking I should just refill cooling system & leave the old small stat on until engine warms up and try again? I don't even know that the small stat is faulty anyway, but since I was doing the main stat thought I'd do it anyway.

Also wanted to do an oil change but I don't see to have a oil plug key that fits the hole, it sort of looks squarish but my 8mm square key seems to be too large. Tried Halfrauds & Machine Mart but don't have anything that'll fit. Anyone know what the key is?

8mm Sq is correct but they can be a tight fit.
Sump metal is fairly thin so care needed as some plugs may never have been removed as many dealers and garages siphon old oil out via the dipstick hole.
I continue that practice with those I find hard to shift.
Will not risk causing the sump to leak.
The reason is that surprisingly the subframe prevents changing a sump insitu.

John

Hi endorfin,

Wit respect to the sump plug I had the same problem so I made a key. See attached photo. The square section at the end was ground from an old bolt. The square is 7.5mm across the flats.

Hope that helps.

cheers
noz

I asked my brother who did the last oil change & he said he drained it from the sump. Has a set of oil drain keys which are the same as mine so it must be a tight fit as you say...will have another look as soon as the rain lets up!

Any ideas on the stuck bolt on the aux stat?