Holes
 

DAVID: As Mintee says there is a very small relief in the Chevy rim, so small that I didn't spot it and drilled experimental holes on the first attempt.(Meziere themselves advised me to drill two 4mm holes in it)You can see it if you hold it up to the light.
PAUL: If you are using the British housing them you have to be careful if using a different thermostat to the one supplied. If the new 'stat has a thinner
profile around the edge then it may allow coolant to seep through when it is closed, I did say, several pages ago that it might be necessary to use some sealer on the rim. The Meziere housing comes with a gasket which sits over the rim of the stat so there is no problem there.

Yes.
Didn't measure it. Pretty small.
In what way? I think any 'hole' is only there to avoid a possible air lock. I doubt it does much (unless it is pretty large) to effect the operation of the thermostat.

In the way that it now seems my thermostat is exactly the same as yours and Wuzerks but I see temperatures of 103 from time to time whereas you guys get nearer 88+-2. I was hoping there would be an obvious difference, but alas not.

So when you drilled your experimental holes, what was the impact?

Are you using one their 195°F Chevy thermostats? Why not try another, slightly lower operating temperature one? They only cost a few quid and are trivial to change.

Holes
 

DAVID: I drilled one hole in my first Chevy 195F(90.5C) 'stat and, although It improved my temperatures well, It was not by as much as I expected. My previous best was 74C with the original failed item. On the second 'stat I drilled a smaller 1mm hole only,(before I spotted the inbuilt bleed hole). I have now blocked the 1mm hole with 2 part epoxy. I think that it is highly likely that you would get lower readings merely by fitting another Chevy 'stat since everything else is the same as mine and Mintees.

yes I am using the 195F chevy stat. I'll try drilling a small hole first, nothing to lose. Meziere suggest two 4mm holes, but that seems a bit drastic.

http://cgi.ebay.co.uk/Rover-75-MGZT-...-/370476153133

Good idea or dangerous for the engine????
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As it happens I bought a spare chevy stat at the same time at the first, so if the hole has no improvement then I'll swap it with the spare.

Housing
 

PHILJUDO:This is the British made version of the Meziere(USA) in line housing. Quite a few of us are using this system now. I have had no problems after about four months use.