WWDiesel wrote:
jagster936 wrote:
Wow thanks for all info! That’s one crazy looking thermostat lol never seen that. Guess it’s embedded or something. Is this a hard job? I’m mechanically inclined do all work myself.
It’s surprising it did go to full temp when AC was on if thermostat is running open. Under light loads I would expect it To run cold also with AC on In summer if cooling system is working properly.
Maybe it’s only partially stuck.
That’s a huge temp jump from one tick less to straight up! Not linear at all lol. The chime / red tick comments don’t seem to Match on the picture.
Correct, gauge is
NOT linear and most say not even real accurate to boot.
This thermostat works somewhat different than most engine thermostats.
It starts out with all coolant bypassing the radiator and flowing through the bottom of the thermostat housing through a "Bypass" circuit. This ensures 100% coolant flow through the head during the critical warm up stage of the engine. As the coolant absorbs heat from engine operation, it slowly closes off the bypass circuit and at the same time opens up the flow circuit to the radiator to maintain the 176 deg.F temperature. So, if the wax bulb in this thermostat fails for any reason, even fully or partially, it will fail to the open position allowing coolant to flow through the radiator at all times and not raise the coolant temperature up to 176 deg.F and instead allow the coolant temperature to in fact run "to cool". In your case with the AC running, it was adding enough heat to the coolant to overcome the partially failed thermostat and raise the coolant temperature up to the desired 176 deg.F operating temperature.
The thermostat is a "sealed unit" type of thermostat and the only option is to replace it with a new one when it fails.
LOST member Jeff aka Turbo-Diesel-Freak has developed an aftermarket thermostat that has serviceable/changeable internals, but in my last conversation with him he said due to some logistic problems he currently does not have any for sale. They are very nice, but they are not cheap!
As to the changing of the thermostat, if you are mechanically inclined and you do most of your own work you should have no problems changing this thermostat. Three 6mm bolts (use 10mm socket/wrench) and several hoses to R&R. It is a tight fit in it's location, but it's doable.
See this thermostat "Remove & Install" writeup by LOST member Squeeto:>
viewtopic.php?p=712186#p712186Fellows... just a heads-up on the Hot Diesel Solutions Model 001 engine thermostat assembly... I am indeed still manufacturing them, but I am not allowed to sell them through this forum.
In all other markets around the world, the CRD engine gets an O.E. thermostat assembly with a 195 degree Fahrenheit valve inside. We here in North America get the 176 degree Fahrenheit valve in the O.E. assembly because lowering engine operating temperatures lowers NOx emissions to meet the EPA's ridiculous standards. The end result is indeed lower NOx, but at the expense of long term engine reliability and poor fuel economy. Even a NEW O.E. thermostat is not good for this engine.
Cooling system bypass circuits have been around for as long as there have been liquid cooled engines. They are VERY necessary to keep engine temperatures as even as possible by allowing coolant to scrub off heat from the hottest parts of the engine and re-circulating that heat to other parts of the engine, even when the radiator circuit is shut off because the engine is not at full operating temperature. Not having a bypass circuit will cause problems with head gasket integrity and with the cylinder head warping because hot spots will form around the exhaust ports if coolant is not allowed to flow around the engine at all times.
Bypass circuits used to be "open" circuits because until the last 30 years or so engines did not make enough power, (and the resulting increase in heat generated by that increase in power), to require the bypass to be shut down. Today's engines make a lot more power - and therefore a lot more heat - requiring engine cooling systems to be more efficient as it is not practical to keep making the cooling systems larger and larger. Shutting down a bypass circuit with a thermostat valve that has a spring loaded bypass valve when the radiator circuit is opening up forces ALL of the coolant to go through the radiator, thereby increasing cooling system efficiency because none of the hot coolant intended to go to the radiator will be re-directed through the bypass. When working any modern engine hard by running at high speeds, driving up hills, towing a load, operating in hot climates or any combination thereof, having ALL the coolant go through the radiator circuit is with no coolant bleeding off in the bypass circuit is highly desirable.
The valve in the O.E. thermostat assembly is is not that unique... lots of engines now incorporate a valve controlled cooling system bypass circuit in an effort to increase cooling system efficiency. The Chrysler Hemi V-8 engine has the same type of thermostat valve. The only thing that can be said about the CRD engine thermostat that makes it unusual is that it is encased in it's own housing, but that would be unusual only for vehicles in the North American market. Thermostat assemblies like that used in the CRD engine are quite common on European engines. Designing any part like this tends to scare away the aftermarket and the jobber parts manufacturers, leaving the owner of a vehicle with non-serviceable assemblies at the mercy of the auto manufacturer and their dealer network with their infamous heart attack inducing parts prices.
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