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1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 09-27-2004, 12:18 PM   #11
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Until the thermostat opens, the coolant in the engine near the thermostat isnt moving. Convection (hot rising, cool falling) means that the coolant right around the thermostat must pick up to AT LEAST (and then well past) the thermostat opening point before it reacts by opening. By the time it opens, the coolant is over that rated temperature - meaning it has to play "catch up". For proof - next time you jump in the car with the engine cold and then get it up to operating temperature, you'll see the thermostat open (late, higher than its rated temp), then the coolant temp falls down below its rated temp, then it swings back higher again and finally settles on its happy place. It doesnt seem to matter whether its a standard stant or Robertshaw type, they all seem to do it.
Great explanation. This is what I mean by heatsoak.
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Old 09-27-2004, 12:25 PM   #12
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Why Drill Holes in Your Thermostat?

I guess the obvious reason is to keep your car cooler therefore controlling KR. However the holes only reduce overall engine temps by about 5 degrees so we have a much more important reason for this.

While at the track you open the hood, maybe ice the charger and let the motor cool down between runs. This may bring your coolant temps down to very low levels, which is good however these cool temps may actually slow you down. With the coolant and engine cooled down there is no coolant circulating until the engine temps reach the temp of the Thermostat.

This would normally be OK however when you're racing the combustion chambers heat up very quickly. So the coolant around the cylinders and heads might reach 250 degrees before the stat even begins to open. This is very bad and can cause high levels of KR in the back half of the ľ mile. By drilling the holes in the thermostat you can eliminate this problem because you will always have a small amount of coolant flowing.

"Performance blasting down the ľ mile isnít the only advantage of having holes drilled in your thermostat. If you live in a colder climate this $11 investment might just save your cylinder heads from being cracked and damaged from the sudden dive in coolant temperature as your winter chilled radiator dumps ití* freezing coolant through your heads.

A drilled stat would be much more forgiving by providing a continuous flow of coolant and reducing sudden and drastic temperature changes."

- Andy H
Duluth, MN
1999 Grand Prix GTP
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