That is the question; just had to put a new stat in my Corolla; the factory ones come with a jiggle valve, the Stant ones do not, so I drill a small hole in the flange and positioned it at 12 oclock when installing. I know the jiggle valves sort of seal when the flow goes through the thermostat, preventing overcooling. I'm curious if just a small hole will make the car not get up to temp in very cold weather. Thoughts? Who's drilled a stat and had a car in very cold weather?
Thanks
Thermostat; to drill or not to drill a bleed hole?
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I'm on the other side-a small hole is going to allow MUCH less coolant through than the factory bypass will-DRILL BABY DRILL!
If the OEM one has a hole, the replacement needs to.
I wouldn't use that stat if they don't look identical in functionality. I learn 2 painful lessons of going old school all metal radiator from CSF and a STANT radiator cap, that's 2 warped heads and head rebuild.
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drill.
my oem isuzu had a small hole with a "wiggle valve" to keep hole clean.
two aftermarket stats I looked at did not. I bought a gates and drilled a hole.
you need a hole to allow quicker flow and stat warmup and to bleed air.
small hole size down from 1/8 inch
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Return the one you bought and get an OEM.
That jiggle valve does something. I saw a 6 to 8 degree drop in operating temps on my Toyota 3.4L installed at the 12 o'clock position.
OEM is out of the question; dealer doesn't have one, don't have time to order. I've tried Motorad and it ran too cool; I've had good success with Stant in the past, so that's what I used.
Car is running good now; before, it was overcooling in cold weather and starting overheating yesterday; lower hose (inlet side thermostat) was ice cold - old stat was sticking closed.
Thanks for the input so far fellas, I'll report back after a few days if anything abnormal occurs!
What year is the car, a 1993? 
Not having more than an opinion on the subject I'd defer to the OEM setup.
I learned the hard way years ago to only use OE thermostats. Since that isn't an option, if the OE part had a bleed hole, I'd be inclined to drill one. My OCD 'might' have me order a thermostat from the dealer and replace the aftermarket part when it comes in.
Do not drill a hole. The replacement has a different style of bleeder. Usually a groove cut into the piston. An extra hole will make it take too long to warm up.
I do believe Lesson #1 regarding buying OEM parts IS the thermostat lesson.
I was told the reason a hole is in the plate / body of the stat was so no pressure built up on either side of the stat.
Don't know what to think now.
I do know a Stant brand (via AAP as I too had no alternative) stat hung up on the casting of the block of the '04 Camry Toyota engine I installed one in.
Tinny garbage compared to the Toyota unit.
Use OEM thermostat.
Get an OE one with the jiggle pin and forget it. I wouldn't put that scrap metal in there especially now the weather is getting cold. Stant another good old name gone bad.
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