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!

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

Vortecs don't have the water pump bypass. Also the water pump bypass is a pencil sized bypass the heater bypass circulates a lot more water. Another thing is the bypass does not send coolant back to the radiator, it just circulates it through the block and heads.

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

It's not redundant to improve the flow of the bypass when it seems to be insufficient. These trucks came with a reliable ignition system. So someone could say going to HEI is redundant under the same logic.

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

Never have and don't plan on ever doing it. If the truck is filled right with coolant and checked then no need for it.
Tim the HEI is a upgrade to the system for better reliability, not to bypass what is there. :chevy:

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

the hole is intended to blead any air that is in the block or heads. if air remains around the thermostat it will not transfer heat to open the thermostat and effectively as water would. and your engine may overheat while the radiator remains cold.

its a small hole to blead air not to by pass so dont go overboard like in some of the pictures above.

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

I agree, The hole serves a different function than a bypass. The hole allows air to escape, too big of a hole will allow water to flow to the radiator taking longer for your motor to warm up. The bypass prevents the heads from overheating and cracking by keeping water moving through the block and heads until the thermostat opens, it does not allow water to flow through the radiator.

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

I ended up not drilling a hole and have been running perfectly fine for about 2 weeks now. I think it's key just to be sure to get all the air out of the cooling system and you should be good to go.:chevy:

Say what?
The heads already have flames traveling through them.

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

Absolutely drill the hole, no reason not to if it doesn't have silver metal floppy thing in the stat., most newer ones have it. The hole lets the air out of the engine if required.
The water pump bypass will not let air out of the top of the engine.

On a new engine install or where the engine gets drained by changing a water pump or freeze plug air gets trapped and will not come out.
To ensure the engine is full I always remove the water hose on the intake and fill until I see water there, then replace the hose. I do that on every engine when first installed, (Not just small block chevys, foreign or domestic) I find a top water source and remove the hose, plug etc to ensure the engine is filled....otherwise it most likely will overheat and loose the coolant. The you have to start over, filling again.

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

Randy is spot on. If your block has been drained for any reason you can save yourself plenty of time and the potential of lots of grief to just spend two minutes drilling an 1/8" hole. Once the system is filled and the air is bled out the hole will serve no purpose and will have no effect on the cooling system. Two minutes of your time may save you $2,000.00 - $10,000.00 any questions.

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

Bump for a 2-month old thread. Have owned my K20 for 41 years, never had a hole in the thermostat, never had a problem. Now there's a problem and I'm gonna drill a hole just in case it helps. Sounds like at the very least, it can't hurt.

Coolant was changed last year for the umpteenth time. Truck is rarely driven anymore but on a trip to town this spring, the heater/defroster stopped blowing hot air, just blew ambient. Temp gauge was normal, and the heater hose going to the core was hot to the touch, but the return hose was cool. First time that's ever happened. Truck sat for maybe an hour, then drove it and all was normal. I was told it might have been an air bubble problem.

The other day I was cutting firewood and the same thing happened. I have a sealed system with a coolant recovery tank and everything appears to be working as it should. I just backflushed the heater core and the water flows through nicely and comes out clean, so no apparent blockage in the heater core.

If the problem was air in the system, I'm hoping the thermostat hole will eliminate it. I'll update this thread in a few days or so with the results.

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

My 94' boat with the LT1 Corvette engine in it came from the factory with a hole drilled in the thermostat....(I have 2 thermostats actually).

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

You may have a thermostat that is sticking. Since you are going to have it out to drill it test it in a pan with a thermometer (several times minimum) just to make sure.

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

I think that these engines are a bit different from the ones produced from '55 until whenever. These never had a hole in the thermostat. Not picking on you; just pointing out that the first 40+ years of production never had a hole in the thermostat...or even two thermostats.

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

Ahhhh, too late, I have already drilled the hole and replaced the t-stat. I did check it in a pan last year when I flushed the system and put in fresh Prestone. I suspect the t-stat is OK because the truck warms up normally and doesn't overheat.

I just came back from a short test drive and the problem persists -- 5/8" heater hose gets hot, but 3/4" hose to radiator stays cool. No flow through the heater core equals no heat from the vents. I suppose there could be air trapped in the heater core and if so, I hope it will work its way out now that there's a hole in the t-stat.

It's just very frustrating because it has never happened before, and I can't seem to figure it out.

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

Any Chance there chould be a block in the heater core?