Optimum thermostat for 1969-1971 Z?

[Kerrigan]

For and driving environment like Oregon and Washington, what is the best thermostat for the early 240Z? I find them in 160F, 170F, 180F, and one other degree-rating I can't locate at the moment. Thank you!

[djwarner]

The best temperature thermostat for any car is at least 185 F(180 will do). This is not for the coolant - but rather for the oil. Oil will actually absorb a small amount of water - say 1% by volume. Heating the coolant to 185 F drives off any water leaving pure oil.

Where does the water come from? The metal in the engine is a very efficient radiator of heat. In fact, overnight, the engine will actually cool below the ambient air temperature. If you live in an area that drops to near the dew point at night, water vapor will condense on the inside and outside of the engine much like moisture forming on the outside of a glass of iced tea.

If the engine never reaches the 185 F point, water continues to accumulate and does bad things since it does not have the lubricity of oil.

Devices without a circulation system, like the bearing boxes on industrial pumps, are carefully designed to reach 185 F in operation. Also this is why the second number in multi-weight oils are specified for viscosity at 185 F.

[AZ-240z]

To add to what djwarner said, I would make sure it is a OEM Nissan thermostat. If you search previous discussions on thermostats, there is

a difference!

[Zedyone_kenobi]

Okay, Any warm surface will cause water to evaporate faster than say just 70°F ambient air. But why 185. Natually 185 would cause water to evaporate faster than say 170, but why do you say 185 is the cut off point?

plain Water will boil at 212, water with coolant even higher. Allowing the oil to reach 212 would guaranty your engine oil is free of water.

[Zed Head]

Don't forget to factor in boiling temperature depression due to intake vacuum on the PCV system!

Nissan got more specific on thermostat temperature choice after 1972. Here's the 1976 chart. You still have to figure out Tropical and Cold. There's probably some general world-based definitions out there somewhere.

[djwarner]

The 185 F temperature was found to work empirically many years ago. Water boils at the temperature it does due to surface tension and atmospheric pressure. Water molecules are slightly bi-polar, with the two hydrogen atoms on one side and the oxygen's fat a** sitting on the other. This make the hydrogen side more positively charged and the oxygen side more negatively charged. The static electrical charge tends to make informal chains of molecules, raising the surface tension.

Oil has few, if any, bipolar sites to stick the water molecule to. Thus it takes less thermal energy to rip the water molecule from the oil surface.

[John Coffey]

So... you're saying to choose the cooling system thermostat opening temperature to boil off water in the oil? I have never heard that before. That would require an oil temp gauge.

I suggest that the OP refer to the FSM picture in Zed Head's post above to select the correct thermostat temperature.

[djwarner]

Light aircraft engines do have an oil temperature gauge. In fact, managing heat shedding is a major design consideration. Most heat is expelled with the exhaust gases. The next most significant heat shedding comes from air passing over the cooling fins. However almost as much heat is carried away by the engine oil - something like 20% if I recall correctly. The oil heat dissipated through the oil sump but most heat is dissipated in an oil cooler.

There is a thermostatic bypass valve at the inlet to the oil cooler called a vernatherm valve. Lycoming specifies that the valve should bypass the oil cooler for oil temps below 185 F. In fact Continental recent announced a warrantee service bulletin to replace vernatherm valves allowing any oil into the cooler at 160F or below.

Why don't we have oil temp gauges in our cars? Costs I imagine?

[Zedyone_kenobi]

Lycoming, Continental.... you sound a lot like my dad who passed away in 2012, who was a certified A&P mechanic and instructor. I get all my anal mechanical tendencies form him.

Oil most certainly does cool the engine, ask any 911 owner, who engines are primarily oil cooled supplemented by air. I agree with you. The 185 number I could see I suppose for suspended H20 particles without the benefits of surface tension to keep them bound together, as well as the PCV system. But I would wonder if the PVC system connected to our SU air cleaner was capable creating less than atmospheric in the engine case.

Still great thread here full of neat bits of info.

For what it is worth I run a 190 degree nissan thermostat in my Z, with a 60/40 water/coolant ratio

Edited July 1, 2014 by Zedyone_kenobi