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Old 01-02-2011, 04:33 AM
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To Drill or Not To Drill Thermostat

Can someone enlighten me as to drill or not to drill holes in the 180 degree thermostat on a 327 Chevy Engine. Been running a 195 degree thermostat and it runs too hot. I'm running a manifold fan sensor that turns on my fan at 200 degrees and cools to 185 before shutting off. Most people tell me to drill 3 small holes in the stat before installing.

If so......what size holes? Also, what is the benefit of doing this?

Thank you

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Old 01-02-2011, 05:12 AM
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1/8 in will do it, not real necessary if you are using a good thermostat. JMO
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Old 01-02-2011, 05:19 AM
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When does it heat up? Driving, cruising, traffic?

In my opinion, I don't think drilling is going to help you. Drilling the t-stat is to bypass coolant before the t-sat opens or to help burp the air pockets out. I drilled mine on my BBC because I have no prevision for the factory style bypass. Once the t-stat opens it doesn't matter if it is drilled or not. You could try a high flow stat.

The manifold is about 10* cooler than the head.

Also, what type of shroud do you have?

I would just put the 180 in without drilling and lower the temp at which your fan(s) come on.

Last edited by NOlowrider; 01-02-2011 at 05:26 AM.
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Old 01-02-2011, 06:39 AM
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Some things that will make it run hotter than you'd like:

Not enough fan air flow thru the rad.

Not enough airflow thru the rad at hiway speeds.
Not enough idle spark timing.

Defective vacuum advance.
Are the heater hoses hooked up?
Add some Water Wetter to the coolant.
Collapsing lower rad hose. (missing hose spring)
Air trapped in the coolant system.
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Old 01-02-2011, 06:40 AM
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Quote:
Originally Posted by F-BIRD'88
Some things that will make it run hotter than you'd like:

Not enough fan air flow thru the rad.

Not enough airflow thru the rad at hiway speeds.
Not enough idle spark timing.

Defective vacuum advance.
Are the heater hoses hooked up?
Add some Water Wetter to the coolant.
Collapsing lower rad hose. (missing hose spring)
Air trapped in the coolant system.
X2 this is all very true.


Cole
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Old 01-02-2011, 07:22 AM
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A partially or mostly plugged radiator (inside core) will overheat or run hot at hiway speed also and can be cool enough at idling speed.You burn less fuel at idle so less heat is spent ...hence if it is borderline it can still keep up.
BTW how HOT is HOT. I see a lot of guys who think 205- 210 is too hot. For a mostly stock later model this is normal. depending on your build this may or may not be too much.You need to verify temps with an infrared gun.
I drill any thermostat without a pellet if the cars hood profile is pretty low.I dont recall EVER drilling a chevy
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Old 01-02-2011, 08:05 AM
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Drilling two 1/8" holes 180 degrees apart from each other will..1st allow some coolant to flow past and 2nd allow any air bubbles that could get stuck to purge.
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Old 01-02-2011, 08:08 AM
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thermostat

about 3 or 4, 1/8" holes will be fine. mainly to make sure the sys is not air bound. try a 160° stat.
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Old 01-02-2011, 08:08 PM
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Quote:
Originally Posted by Sweet-34
Can someone enlighten me as to drill or not to drill holes in the 180 degree thermostat on a 327 Chevy Engine. Been running a 195 degree thermostat and it runs too hot. I'm running a manifold fan sensor that turns on my fan at 200 degrees and cools to 185 before shutting off. Most people tell me to drill 3 small holes in the stat before installing.

If so......what size holes? Also, what is the benefit of doing this?

Thank you
as was suggested,a good fan shroud forces air to be pulled thru radiator.larry nice rod
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Old 01-03-2011, 12:25 AM
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if you have a heater core hooked up, will the holes really help? since the heater core acts as a bypass around the t-stat anyway?
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Old 01-03-2011, 05:56 AM
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A lot of vehicles shut the heater flow off when not actually wnating heat.
Prety sure all AC cars do this.

If there is no valve hooked up the the heater core to shut off the water flow, a bypass should not be needed.

Not having a bypass can create some strange temp patterns util the car fully warms up-----even if there are a couple of holes drilled into the t-stat.
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Old 01-03-2011, 06:16 AM
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This is copied and pasted directly from Stewarts Water Pumps website: http://www.stewartcomponents.com/index.html

"Tech Tip #3 - Thermostats & Restrictors

Thermostats & Restrictors
We strongly recommend NEVER using a restrictor: they decrease coolant flow and ultimately inhibit cooling.

For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robertshaw high flow thermostat. This thermostat does not restrict flow when open. The Stewart/ Robertshaw thermostat enhances the performance of the cooling system, using any style of water pump. However, the Stewart Stage 1 high-flow water pump may require this thermostat to operate properly, and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses.

Stewart further modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM.

A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.

Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it."

I'm using one of their pumps and have done this mod to my thermostat. With a 190* stat seldom does the195* fan setting ever turn it on unless the car has idled for quite a while.

Dave W
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Last edited by Irelands child; 01-03-2011 at 06:19 AM. Reason: Make sense!!!
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Old 01-03-2011, 07:41 AM
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I always drill one 3/16" hole when I install a t-stat, any more than that and you're defeatting the purpose of a t-stat, anyless and you can get air pockets.

High system pressure, high flow, about 30% antifreeze has always worked very well for me.
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Old 01-03-2011, 09:03 AM
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I drilled my stat, too. My understanding is this is mainly to allow air to escape the block when filling the system. I would think the amount of coolant flow through such a small hole would be insignificant.
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Old 01-03-2011, 11:28 AM
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Quote:
Originally Posted by ap72
I always drill one 3/16" hole when I install a t-stat, any more than that and you're defeatting the purpose of a t-stat, anyless and you can get air pockets.

High system pressure, high flow, about 30% antifreeze has always worked very well for me.
30% antifreeze will get you a cracked block in Michigan :>
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