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

[garyd1961]

Originally Posted by davepl

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

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.

[special-K]

Originally Posted by davepl

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

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.

[Andy4639]

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.

[mike16]

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.

[garyd1961]

Originally Posted by mike16

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.

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.

[1969 Project]

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.

[GRX]

Originally Posted by K20super

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

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

[randy500]

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.

[CaptRMW]

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.

[Stocker]

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.

[Ski-me]

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).

[HO455]

Originally Posted by Stocker

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.

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.

[Steeveedee]

Originally Posted by Ski-me

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).

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.

[Stocker]

Originally Posted by HO455

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.

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.

[gearheadperkins]

Originally Posted by Stocker

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.

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

[BRL]

Originally Posted by Stocker

...I just backflushed the heater core and the water flows through nicely and comes out clean, so no apparent blockage in the heater core...

Doesn't sound like it.

[Stocker]

Update, and some speculation on my part. The good -- it seems to be working. The bad -- I do not know why.

Spent a good chunk of the day chasing vacuum lines and tearing into the HVAC control assembly. Didn't really find anything but got some old dust relocated. At one point I applied vacuum off & on repeatedly to the water control valve (on the inner fender). It may have been stuck in the closed position because it suddenly allowed coolant to circulate and voila, the cab had heat! I hadn't suspected it because it was installed new just last year.

So, I hope that's fixed and I can move on to another new, failed A/C clutch. After I replace the leaking t-stat gasket...... Seems like it has been one thing after another for about a year now. After 41 years I am quite attached to the old girl but the never-ending annoyances & inconveniences are wearing a bit thin.

[leddzepp]

I’ll bet that valve was stuck, I’ve had that happen before with a new one as well...glad you got it fixed

[GRX]

Originally Posted by leddzepp

I’ll bet that valve was stuck, I’ve had that happen before with a new one as well...glad you got it fixed

Agreed. May not have been the case here, but I have seen an errant piece of gasket or sealer get lodged in the stat spring more than once.

[NoNeck]

The coolant should not flow until the thermostat opens. That's it's job... to regulate engine temperature. It doesn't help cool. It stops flow to keep things warm in a properly functioning and sized cooling system.

I sometimes drill a 1/8" hole in them. But not all the time either. It only helps when filling the cooling system after it has been drained. The objective is to not have any air trapped in the heads or block after the system has been run and cycled. Especially if it's a coolant recovering type system where the coolant is drawn back into it while things cool down.

Whatever you do, don't drill a series of 2 or 3 holes. That would simply weaken the effect of having a thermostat in the first place. It would take forever to get warm air to the heater on a cold winter day.

Bottom line, a single 1/8" hole drilled at 12 o'clock on a quality stat helps to eliminate dreaded air pockets.

POP

[WorkinLonghorn]

I thought this info from the Stant website was interesting;

"My thermostat has a jiggle pin but the Stant thermostat doesn't. Will a Stant thermostat still work?

Yes. Many thermostats have a “jiggle pin” that allows trapped air in the cooling system to pass through the thermostat and be released from the system. Some Stant thermostat do not use have a jiggle pin. These thermostats will have a "bleed notch” or other method of removing air from the system."


"As the engine's coolant warms up, the increase in heat causes the wax to melt and expand. The wax pushes against a piston inside a rubber boot. This forces the piston outward to open the thermostat. Within 3 or 4 degrees F. of the thermostat preset/rated temperature which is usually marked on the thermostat, the thermostat begins to unseat so coolant can start to circulate between the engine and radiator. It continues to open until engine cooling requirements are satisfied. It is fully open about 15-20 degrees above its rated temperature. If the temperature of the circulating coolant begins to drop, the wax element contracts, allowing spring tension to close the thermostat, thus decreasing coolant flow through the radiator. "


http://www.stant.com/index.php/engli...rmostats/faqs/


Although frankly, I don't see how air would survive the first time that you got the thermostat fully open and coolant was gushing through there to the radiator. And of course the coolant going into the engine again is from the bottom of the radiator, so no air there.

Never drilled and won't start now! -BA

[BCOWANWHEELS]

in calf. I,d go 160 all stock personally