Manufacturing Defect in the Stant 14068 Thermostat

Updated on 29-Jan-12. See the bottom of the page.

In about September of 2011 we ordered five 14068's from Rockauto. One of them had the wrong bypass valve spring. I did not think too much of it until we ordered ten thermostats from Summit Racing in December of 2011. One of those units had the wrong bypass spring. Summit shipped the thermostats from the manufacturer's warehouse.

The bypass valve is designed to open with five psi of pressure. When the bypass valve is depressed .5" the spring exerts five pounds of pressure on the valve. The defective thermostats have a lighter spring that exerts 1.5 pounds of pressure when the valve is depressed .5".

A defective thermostat with the light bypass spring is on the left. A normal thermostat is on the right.

The normal thermostat opens to protect the radiator from over pressurization when the backpressure at the inlet of the radiator is five psi. It does this at about 5000 rpm. I believe that if the defective thermostat is installed, the engine will run warmer from about 1000 to 3000 rpm because the radiator would have less flow due to the early bypassing.

Stant was the supplier OE LT5 thermostat. It's a specially designed unit that is used only on the LT5 engine. It has a unique rubber insulator around the wax valve sensor. I believe that the insulation is used to minimize the thermal conductivity from the sensor to the housing. The housing tends to run cool because it is remotely located about 12 inches away from the engine. A cool housing can delay the opening of the thermostat which will make the engine run warmer since the coolant can't flow through the radiator when the thermostat is closed.

We are fortunate that Stant still supplies this unit. I have notified Stant of this observation. If I receive information from Stant I will post it here.

AutoZone sells a thermostat for the LT5. Duralast pn 4068. It is not made by Stant. It does not have the insulation around the wax stat. It also does not have the two slots in the bypass valve that allow a small flow of engine heat to the thermostat sensor when the engine is cold. We tried this unit and found that the engine heated to 205 degrees before the thermostat opened. A normal Stant 14068 opens at 185 degrees. We don't recommend the Duralast 4068.

As listed in the ZR-1 owners manual, and GM service manual the OE LT5 thermostat is specified as opening at 180 degrees.

Update 29-Jan-12. On 19-Dec-11 I notified Stant via email to their customer service operation. As of this date I have not heard from them.

Update 25-Jun-12. I have not heard from Stant. I received ten thermostats from Rockauto. They all passed inspection.

Update 20-Dec-12. Received ten thermostats from Rockauto. They all passed inspection.