The thermostat controls the MINIMUM operating temperature of the engine.What was the temperature rating on an OEM 1964 390 thermostat? It looks like the options are 160, 180, or 195. I'm inclined to believe it's 195. Thanks gang.
My listings (take with a grain of salt) show 195°. However, as the others have stated, I prefer to use the temp that benefits the intended use. While the rated temp is the 'cracking' temperature for the thermostat and sets minimum temperature, typical operating temps are 5°F to 15°F above that. In no case should the system exceed 20° above or (as JEM said) you have cooling system or related failures. Note here that the factory had their reasons for the temperature they chose, but our reasons may be different. To that, I will take a moment to throw my 2-cents in with JEM's good stuff to show why I might choose one rating over another:What was the temperature rating on an OEM 1964 390 thermostat? It looks like the options are 160, 180, or 195. I'm inclined to believe it's 195. Thanks gang.
:tup: This is important to remember if diagnosing an under or over-temperature issue, as well as setting your own intended operating range.The thermostat controls the MINIMUM operating temperature of the engine.
The cooling system capacity - radiator size and airflow through it - controls the MAXIMUM operating temperature.
In a perfect world they're not far apart.
Here I counter with lower temperatures making more power. There are different reasons for different temperatures, and compromises for how each is used in the particular application. So, colder means more power. This is why engine dyno operators looking for big numbers will often run the engine at 140°F or colder. Conversely, engine wear is less as you get colder, with the curve bottoming between 160°F and 175°F. OK, so that would indicate maybe running a little warmer than a max-power application.I generally use 180ish. There's no benefit to going any colder. 195 would be okay, but once again the real question is making sure you've got enough cooling system capacity to keep the temperature from going much above the thermostat number.
Agreed. There's that 20°F range again, and the choice of rating may depend on the whole system's ability to cool - e.g., typical running temps. Adjust from there if cooler, of upgrade the system if hotter. So, if your system is so good it runs all day at 165°F on a 160°F thermostat, you might want to raise the rated temperature if you need a higher average running temperature.Most US production cooling systems back in the day were not built to cool an engine run at high load for prolonged periods, so the cooler thermostat provides a little bit more margin during incremental heavy-load operation. If you've got enough water pump, radiator, fan, and airflow to keep the coolant temps at 200degF at sustained high load you won't have a problem using a hotter thermostat.
True enough for many older factory EFI systems that use 'step' warm-up control. One advantage to newer and aftermarket systems is the full range control, or lack of steps. In this case, the AFR is maintained at the correct ratio no matter the actual engine temperature.Use of a cold thermostat in EFI cars will often fool the control system into staying in cold-start mode, running rich and dumping too much fuel into the engine, so if you really want to run that 160deg thermostat you need to double-check the temperature-mixture mapping.
Yes, in a controlled situation...I remember a tour of Steve Dinan's facility some years ago when he was explaining that if you wanted the best dyno numbers you'd run the car until it was very hot - get the engine oil, the transmission oil, the rearend, wheel bearings very hot so that the lube would be as thin as possible - then you'd introduce cold coolant into the engine as quickly as you could without breaking something and do your runs and take your number.Here I counter with lower temperatures making more power. There are different reasons for different temperatures, and compromises for how each is used in the particular application.