layback40 wrote:
Another issue with inline thermostats is that they dont have coolant circulating around the engine only. In cold climates you may not need much flow through the radiator. The bypass system keeps the coolant flowing around the engine & so helps prevent hot spots. There is no advantage for the inline unit. The R428 was designed to have continuous coolant flow through it & we should respect that.
Essentially, you are correct in that inline thermostat valves only control coolant flow through the radiator circuit. And, THANK YOU for saying that the original design of the R428 should be respected. SO MANY CRD owners do not respect the original design OR basic internal combustion engine design and engineering principles.
However, ALL liquid cooled internal combustion engines have a bypass circuit because all liquid cooled IC engines will develop hot spots in the cylinder head, (increasing greatly the chances of the head warping and exhaust valve failure), if constant coolant flow through the engine is not maintained. It is simply a fact that engines which have an inline thermostat will have an open bypass circuit elsewhere that takes over coolant flow throughout the engine when the inline thermostat valve closes down.
For the record, open bypass circuit cooling systems are not as efficient as cooling systems that have valve controlled bypass circuits because there will always be some bleed through of coolant in the open bypass circuit design, even in times of high demand where you want ALL of the coolant flow going through the radiator. Cooling systems that have an open bypass circuit therefore need to be larger to compensate for the loss of efficiency. All other things being the same, (the type of IC engine, the displacement, the state of tune, naturally aspirated or forced induction, and the intended use of the engine), a valve controlled bypass circuit cooling system will be smaller and more efficient than an open bypass cooling system.
I have an article I wrote that gets into the details of all the reasons why the inline thermostat valve that was popular for solving the cold-running engine problems of the Liberty CRD is a bad idea. I can post it here for all LOSTJEEPS.com members or send it to anyone's e-mail address if they want it.
To those who have claimed that there are no issues using the inline thermostat:
You will not see your problems until you have a head gasket failure. Those failures may not simply be a warped cylinder head, but may also include cracks in the head around the exhaust valves. By the time you discover the problem it may indeed be too late to repair your cylinder head. This damage will occur prematurely because you are essentially running without a cooling system bypass circuit AND/OR you will have an overheat event because you are using the thermostat valve from a Renault R5 rather than at least spending the money for a Meziere in-hose thermostat housing. The valve from the R5 is much too small to flow enough coolant in high demand situations; the Meziere in-hose thermostat housing allows the use of a thermostat valve from a large displacement V-8 engine, (a small-block Chevrolet, I believe).
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