Why Did They Start Putting Thermostats On Lower End Of Engines?
Why Did They Start Putting Thermostats On Lower End Of Engines?
(OP)
Since the beginning of time thermostats have always been at the cylinder head outlet.
Within the past 15-20 years they seem to be trending to the radiator hose inlet.
To me this seems a little strange. Why do we care to more carefully regulate the water temperature around the cylinders than in the heads?
The heads are where all the [heat] action seems to be so it would seem to be more critical to regulate them like it was always done in the Olden Days.
Thoughts?
Within the past 15-20 years they seem to be trending to the radiator hose inlet.
To me this seems a little strange. Why do we care to more carefully regulate the water temperature around the cylinders than in the heads?
The heads are where all the [heat] action seems to be so it would seem to be more critical to regulate them like it was always done in the Olden Days.
Thoughts?





RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
I suspect the move due almost entirely to cylinder heads becoming more complicated with the addition of more valves and much more complicated works to control them (VVT systems of various types) making packing challenges more difficult.
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
with the introduction of various emission regulations over the years getting the engine within its working temperature range as soon as possible after a cold start and keeping it within the optimal range as closely as possible a more refined regulating system is required. by controlling the inlet temperature keeping the amount of cooling within the optimal range becomes somewhat easier because you more or less stabilize the cylinder water inlet temperature depending on the load of the engine. in the classic system where you control the outlet temperature of the head you have less direct control over what happens because the inlet temperature will vary depending on speed, whether it rains or not etc with as a result the engine temperature will fluctuate more. you may also have noticed that regulating the cooling system has been increasingly sophisticated by the use of less fluid volume (leading to faster heating after a cold start) and more then one electrically driven multispeed fan effectively widening the range within regulating is possible. with "classic" system the range was managed by the thermostat only, in modern systems thermostat and fan(s) together do the job, making it possible for a faster reacting system capable over a wider range with less fluid.
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
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RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
PJGD
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
The bypass loop through the heater core is connected all the time and joins in between the thermostat and the water pump inlet. The radiator loop comes in through the thermostat into that housing. One other advantage of this layout is that the thermostat doesn't need a bleed hole to allow a small amount of circulation for it to "see" the temperature. It means the flow through the radiator loop can be completely shut when the engine is cold. For a diesel engine in winter where you want every bit of heat you can possibly get for the interior heater, this is a good thing!
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
The somewhat more complicated re-circulation system and the dual function thermostat, which modulates re-circulation and the inflow of lower temperature coolant, is the down side. We also get to learn a new term: 'de-gassing bottle', with new cooling technology.
It is worth your while to get a hold of a new thermostat which has a disc on the 'back' to regulate the re-circulation flow. You will understand instantly what it is doing - opening one path while closing off another.
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
RE: Why Did They Start Putting Thermostats On Lower End Of Engines?
Steve