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First of all some facts from a Stant technical person: They made the OEM stat for the LT5; the reason there is a rubber seal on the thermostat valve is to minimize coolant leakage, and thereby promote a faster warm-up; all the rubber parts in the OEM thermostat are subject to deterioration and this may change how the stat performs over time. The thermostat valve spring is there to close the valve; and because the LT5 Stat has coolant flow in reverse [Re: the stat] the spring is engineered to take into account that coolant flow effect [flow tends to open the valve].

Now noting that many thermostats seem to have similar construction, I found a Stant # 29306 at Pep Boys [$2.99] that is a 160F stat and has a flange diameter of 54MM. It has a metal to metal thermostat valve. This flange can be reduced to 44mm quite easily with a high speed grinder followed up with a file; this is made even more easy by the fact that the stat has a pressed in circumferential ring at very close to 44mm. The fact that the valve spring is engineered for flow in the other direction is a consideration, but may turn out to be insignificant.

Relative to the coolant bypass valve of the OEM stat: if the application had an after-market all-alluminum radiator, it may be that a bypass valve would be unnecessary. A cylindrical aluminum plug with about (3) 1/8" holes could be clamped into the bypass hose as a substitute.

For stock radiator cars, the reduced flange diameter # 29306 stat can have an OEM equivalent bypass valve attached to it. The way I did it was to take a Stant #35399 [$4.79 @ Krager] stat. I then removed the bypass valve assembly [with a 1/4" pin punch]. I then disassembled the bypass valve to salvage the tubular two diameter part that presses on to the "heat engine" pellet chamber. This fixture allows for a lot of innovation as to how to "create" an OEM equivalent bypass valve. I shortened the small tube end to about 3/8" length. I found that the stainless steel tubing from a set of TV rabbit ears had a diameter that would press fit into the above mentioned fixture. Once "pressed in", the length can be cut with a mini tubing cutter to equal spread of the OEM stat flange to bypass valve measurement. Then one has to create a stop for the valve at the end of the tube. I used ACE hardware # 2014397 rivet [expanded with an allen wrench] resulting in an 8-32 thread fixed at the end of the tube. I then modified a stainless steel flat fender washer to the equivalent of the OEM valve, and created a stop with an 8-32 SS allen head screw with an appropriate stop washer. I found a spring that worked as equivalent to OEM with no modification [#37 at ACE Hardware]. All relevant surfaces were cleaned with alcohol and then the allen screw was locked into the rivet with Locktite Weld and likewise the large end of the attachment cylindrical device [from #2930 stat] to the copper pellet chamber....verifying that it was concentric before the "weld" set up.

The SS bypass valve to SS shaft may be superior to OEM. The fact that there is no rubber rim around the thermostat valve may make this hybrid more durable.



Author: Erle Holm

Other Links:
ZR-1 Products offers 145, 160, 170 F thermostats.

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