T-stat to drill a hole or not to drill a hole?
 

I am getting ready to replace my thermostat and was wondering if it is necessary to drill a 1/8 hole in it before installing , if so what are the benefits? I heard that by drilling a hole it could cause the temp to fluctuate. The PO did not drill holes in the current thermostat and the temp is at a constant 190.

Re: T-stat to drill a hole or not to drill a hole?
 

If it ain’t broke, don’t fix it. I’ve never drilled a hole in one, never had any issues either.

Re: T-stat to drill a hole or not to drill a hole?
 

Necessary? No. Helpful? Yes. It allows the engine and radiator to be completely filled with no air pockets being trapped. Drilling one or or two 1/8" holes in a thermostat creates no issues or fluctuating temps that I've ever seen. Many thermostats nowadays come with holes already in them....

Re: T-stat to drill a hole or not to drill a hole?
 

X2.

Re: T-stat to drill a hole or not to drill a hole?
 

They have the jiggle thing in them though.

Re: T-stat to drill a hole or not to drill a hole?
 

Always drill two holes in them, it stops air pockets.:mm:

Re: T-stat to drill a hole or not to drill a hole?
 

Never drilled holes in any of them over 45 years ,So now it's the thing to do ? :lol:

Re: T-stat to drill a hole or not to drill a hole?
 

Millenials...

Re: T-stat to drill a hole or not to drill a hole?
 

Apparently it's the in thing to do now. This thread is the first I've heard of it!

-klb

Re: T-stat to drill a hole or not to drill a hole?
 

It also helps with aluminum heads because it is not as much of a shock due to temperature change when it opens.

Re: T-stat to drill a hole or not to drill a hole?
 

My t-stat has patina ...:lol:

Re: T-stat to drill a hole or not to drill a hole?
 

I have heard of this before (recently), but have never done it. It came up in a discussion about the lack of wp bypass passage in the L31’s vortex heads and this was brought up as a possible mitigation. Having said all that, I HAVE had an air pocket in a rad and, if this would prevent that. I’m all for it. But I do wonder why, if it’s such a good idea why they didn’t come like this originally and still don’t as far as all the replacements I’ve bought.

What is this jiggle thing you speak of Demian?? :lol:
Hey! I used to live in Lake Forest!!

Re: T-stat to drill a hole or not to drill a hole?
 

I had a Corvette years ago. And they are notorious for running hot. The person that built my motor. Put a bleed hole in the thermostat. And it did run cooler. I think maybe it helps with extra circulation. But it seem to work for me. Just my two cents.

Re: T-stat to drill a hole or not to drill a hole?
 

Just a tad overkill - but yes one 1/8 inch hole drilled helps for the purpose of air pockets

Re: T-stat to drill a hole or not to drill a hole?
 

A bypass hose is what you need not a hole in your thermostat especially on a vortec. The bypass hose keeps the water circulating through the heads eliminating hot spots. I have never know a SBC to have a problem with air pockets, these old trucks ran with air in the radiator.

Re: T-stat to drill a hole or not to drill a hole?
 

It isn't anything new. It is an old racer modification. I was doing it back in the 80's. The reason is that it makes it easier to vent air out when refilling the water. Used to be you were allowed to dump the water out of your radiator between rounds and refill it to cool the motor down for the next round. Some guys used to put little valves in the top of the intake water passages to vent air too.

Re: T-stat to drill a hole or not to drill a hole?
 

$10 says the PO's thermostat has a little notch in the seat to let air through. If such is the case, no holes necessary.

Re: T-stat to drill a hole or not to drill a hole?
 

Thanks Fellas! I don't have any issues with my engine running hot and if the cooling system is bled correctly wouldn't you not have to worry about air in the system?

Re: T-stat to drill a hole or not to drill a hole?
 

FWIW I drilled one very small hole in mine. The heater core looks to be higher than the top of the radiator and I did it to purge air pockets faster. Some thermostats already have a hole with a rivet looking piece that accomplishes the same thing. I have heard of guys propping a thermostat open with an aspirin on reassembly to let air out then the aspirin melts away and the system goes back to working normally. Without a hole I imagine air could accumulate around the thermostat and it would not open as soon but once it did it would purge the air. Probably over thinking it a bit but love the trucks.

Re: T-stat to drill a hole or not to drill a hole?
 

I haven't ever seen an actual flow diagram of the coolant circulation system of a Chevy engine, but I suspect that the bypass port in the SBC water pump or the bypass hose in a BBC probably covers this issue.

Re: T-stat to drill a hole or not to drill a hole?
 

Is it necessary to drill a hole in the thermostat? No, or they would come with the hole already drilled. Is it an effective way to keep a truck running cool as that thermostat allows in a wider set of circumstances? Yes. Is there any negative affect from drilling al 1/8" hole? No, only good. I never did it in all my years till a friend who is an ace mechanic suggested it when my truck seemed to run a tad hot after fresh heads bumped my compression. I'm a baby boomer and he is generation X. If it's a millennial thing to do, there's at least one good thing we can credit them :cool:. But I think it's an old school track trick that has found it's way into the mainstream.

Re: T-stat to drill a hole or not to drill a hole?
 

Drill

Re: T-stat to drill a hole or not to drill a hole?
 

Years ago I rebuilt a SBC and upon its first run my 50/50 mix kept spewing out of the radiator overflow and fill hole like a coffee pot peculator! :mad:

Assumed it was an air pocket trapped in there somewhere and was causing steam.

Removed the thermostat and drove a few days and eventually it settled down, so I put the stat back in.

I read someplace that the hole causes the engine to take a bit longer to warm up but can be helpful if the stat should seize closed.

Re: T-stat to drill a hole or not to drill a hole?
 

Small block Chevrolets have an internal bypass in the water pump, do they not? Seems redundant...

Re: T-stat to drill a hole or not to drill a hole?
 

Could very well be, that was my first rebuild and really don't know what was causing that problem.

ETA: Oh I think I see what you're saying, didn't know SBC water pumps had a bypass.

...oops!