Do It Yourself

Stock C5 / Z06 Thermostat Modification for ~181° F Operation

The reason I decided to do this was that after I purchased several aftermarket units and installed them I found they operated about 8-10 degrees warmer than advertised (Example - 178 running at 187). This was not acceptable since my stock unit ran about 188-190 and I wanted to get down to about 180, hence the D.I.Y. approach. 

What makes the LS-1 and LS-6 thermostats different from most engines is that the thermostat is part of the housing/neck. Most aftermarket units cost about $60

The following procedure was performed on a stock 02 and 03 Z06 thermostat. 

NEVER attempt to service the cooling system while the vehicle is hot. Severe injury can occur as the system is under pressure when hot. 

When the system is cold, or has cooled down considerably, unscrew the radiator coolant tank cap. This will prevent the system from pulling a vacuum while it’s being drained. (I leave the cap sitting on top to prevent anything from falling inside) 

Use a ¼” drive extension to insert into the white radiator drain plug. (This plug is located on the passenger side of the vehicle just inside of the A/C line) The plug has course threads and only requires about a ¼ turn to open fully. The fluid will come out the drain highlighted in the picture.

After about a gallon of coolant has drained the flow will slow down considerably. Be patient as this is not enough to start the thermostat removal process yet. You will need to drain at least a gallon and a half to get the coolant level below the thermostat housing. At this point you can close the plug. You will feel it snap or click into place, this lets you know it’s safely closed all the way. 

Take a pair of channel locks and squeeze the tabs of the radiator hose clamp and slide it up the hose past the first elbow. If your radiator hose does not come off with a twist and pull then you may need to carefully slip a small screw driver between the hose and thermostat neck and rotate it all the way around to break the bond. You will need a 10mm Socket or Wrench to remove the thermostat bolts then the unit should lift right out. 

Now that you have the thermostat in front of you or on a bench notice the large coiled spring and how it‘s coils are larger at the base and smaller at one end. (See picture)

You will need to remove 2 1/8 coils off the smallest part of the spring. (See picture) 

I used a large screwdriver shaft wedged between the 3^rd coil and retainer plate to take the pressure off the spring while I cut it. You can twist the coils around so that the point it needs to be cut at is easier to access.

 Use a Dremel tool with a cutting disc (or similar device) to cut the spring in the proper place (always wear proper eye protection). Be careful not to damage the brass center or retaining plate.

Next grab the piece you just cut with a pair of needle nose pliers or small vise grips so it can be cut in the middle for removal from the unit. It may be necessary to do this twice. You will want to rinse your thermostat in the sink to wash off the metal shavings so as to prevent contamination of your cooling system. The end of the spring will need to be positioned so that it is in the middle of the retainer plate.

If not positioned correctly the motion of the mechanism could cause the spring to rotate and either hang or throw the opening temperature way off!

 You are now ready for reassembly. Don’t forget to check that you closed the drain plug on the radiator before refilling the coolant tank.

 Your results might vary slightly. I was able to achieve a steady 181° F on the highway with outside ambient temperatures ranging from 45° F to 68° F after completing this procedure. 

After making this modification have your fan set points changed by a shop with LS edit. If you own a Predator or HyperTech you can do it with one of these units yourself. Mine are currently set at High speed on 205, off 201 and Low Speed on 200, off 190. These are about 15 degrees below the factory settings

 DISCLAIMER: You perform this modification at your own risk. I make no claims that the information contained in this article is accurate, complete or that it will not damage you and/or your automobile. The information contained herein is strictly for educational purposes and is only from my personal experiences.

David B.

IM4A2Z

 Visitors Since 12/10/2002