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Old 4 Weeks Ago   #1
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Thermostat opening temp

Thought I would replace the thermostat due to very slow warming.
Thermostats are available at 81 82 88 and 90 degrees opening. Which one is normal on a 2.8 jtd?(temperate climate). Maybe a cold climate one ie 90 degrees may be better bet?
I know that they are notorious for slow warm up but it cant help wear, so thought for such a small job it may be worth a try!
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Old 4 Weeks Ago   #2
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Re: Thermostat opening temp

Quote Originally Posted by merovingian View Post
Thought I would replace the thermostat due to very slow warming.
Thermostats are available at 81 82 88 and 90 degrees opening. Which one is normal on a 2.8 jtd?(temperate climate). Maybe a cold climate one ie 90 degrees may be better bet?
I know that they are notorious for slow warm up but it cant help wear, so thought for such a small job it may be worth a try!
a fully functioning stat is there to prevent over heating not to speed up warming the stat will OPEN at the given temperature but from zero to the stat opening setting will take exactly the same time to get to 81--82 degrees etc regardless which stat you have in. I suspect you have a open stat or none at all that's why it takes along time for the engine to get to temperature ie 81--82 degrees plus this weather the very cold air going through your radiator regardless of stat will take a lot longer to get to working temp.
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Old 4 Weeks Ago   #3
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Re: Thermostat opening temp

Yes thanks, so 82 degrees would be normal, its my suspicion too, even takes a long time in warm weather so maybe its stuck open as you say
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Old 3 Weeks Ago   #4
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Re: Thermostat opening temp

It is very rare for thermostats to jam in the open position. The operation of a common wax pellet thermostat is that the wax expands with an increase in heat pushing the central pin out of the pellet. The pin forces open the valve plate. As the thermostat cools the wax contracts. When the return spring pressure is greater than the pressure exerted by the wax in the pellet it closes. It is more common for the thermostat to stay closed rather than open. For that reason I would suspect the thermostat is missing. In older style cast iron engines thermostats were somewhat universal, generally only varying in diameter and opening temperature. In modern vehicles with alloy engines the style and hardware around the wax pellet valve assembly can be varied in design layout. It is important to ensure the correct shape and temp setting is as per the vehicle spec to avoid any problems with overheating when you replace the thermostat. Cheers,
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Old 3 Weeks Ago   #5
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Re: Thermostat opening temp

Quote Originally Posted by Geeco View Post
It is very rare for thermostats to jam in the open position. The operation of a common wax pellet thermostat is that the wax expands with an increase in heat pushing the central pin out of the pellet. The pin forces open the valve plate. As the thermostat cools the wax contracts. When the return spring pressure is greater than the pressure exerted by the wax in the pellet it closes. It is more common for the thermostat to stay closed rather than open. For that reason I would suspect the thermostat is missing. In older style cast iron engines thermostats were somewhat universal, generally only varying in diameter and opening temperature. In modern vehicles with alloy engines the style and hardware around the wax pellet valve assembly can be varied in design layout. It is important to ensure the correct shape and temp setting is as per the vehicle spec to avoid any problems with overheating when you replace the thermostat. Cheers,
Mmmm. Have to disagree somewhat. It is common to see running temps gradually decline with thermostats starting to fail. Most times it is because the temp is running too low that folk replace their stats.
Ian.
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Old 3 Weeks Ago   #6
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Re: Thermostat opening temp

Quote Originally Posted by oigle View Post
Mmmm. Have to disagree somewhat. It is common to see running temps gradually decline with thermostats starting to fail. Most times it is because the temp is running too low that folk replace their stats.
Ian.
Hi Ian, I am very interested in your above comment as it is completely the opposite to my experience. In a former life I worked in the automotive aftermarket. One of the product groups imported into AU by my employer was engine thermostats manufactured in Germany & Israel from a very reputable manufacturer. One of my responsibilities was to process claims when end users or workshops submitted claims for alleged faulty thermostats. In the over ten years in that role I can not remember one claim for a thermostat that caused the engine to run below operating temperature. Just the opposite, overheating with subsequent damage ( often head gasket issues) was the subject of the claims. While I do not wish to bore you with the details of a typical claim, the end result was almost always that the thermostat was a victim of another failed component in the cooling system. The thermostat is simply a valve that in the closed position it separates the radiator coolant from the coolant in the engine. When the coolant in the engine is heated by the combustion process to the temp setting calibrated into the thermostat wax pellet it overcomes the pressure of the return spring and opens. Generally there is a small temperature variation between the "start to open " temp and "fully open" temp, from memory around 5-6Deg C. I hope the above explains why I made the comments I did. Cheers, Gary
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Old 3 Weeks Ago   #7
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Re: Thermostat opening temp

Quote Originally Posted by Geeco View Post
Hi Ian, I am very interested in your above comment as it is completely the opposite to my experience. In a former life I worked in the automotive aftermarket. One of the product groups imported into AU by my employer was engine thermostats manufactured in Germany & Israel from a very reputable manufacturer. One of my responsibilities was to process claims when end users or workshops submitted claims for alleged faulty thermostats. In the over ten years in that role I can not remember one claim for a thermostat that caused the engine to run below operating temperature. Just the opposite, overheating with subsequent damage ( often head gasket issues) was the subject of the claims. While I do not wish to bore you with the details of a typical claim, the end result was almost always that the thermostat was a victim of another failed component in the cooling system. The thermostat is simply a valve that in the closed position it separates the radiator coolant from the coolant in the engine. When the coolant in the engine is heated by the combustion process to the temp setting calibrated into the thermostat wax pellet it overcomes the pressure of the return spring and opens. Generally there is a small temperature variation between the "start to open " temp and "fully open" temp, from memory around 5-6Deg C. I hope the above explains why I made the comments I did. Cheers, Gary
Yes Gary - I knew we were destined to disagree :-)
As a claims clerk, you would have seen claims for overheated engines but I suggest that no claims would ever be made for motors running too cool.
I'm not saying stats never jam shut but I am saying it is rare and much more common to have them opening too early or even not closing fully and causing long warm up periods. On MB forum, there are constant enquiries about motors running too cold and requiring new thermostats. Never seen one for running too hot. My personal experience is as a motor dealer - Nissan and Holden - for many years. Never had a claim for a jammed closed stat but had a few - not many - where engines ran too cool.
I vaguely remember a post from a knowledgeable forum member on the MB forum suggesting manufacturers are very careful in their design to never have stats jam closed as the end result is quite catastrophic. I am unaware of the way they achieve that.

Cheers

Ian.
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Old 3 Weeks Ago   #8
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Re: Thermostat opening temp

Ian, it did occur to me as I was responding to your post that it probably would be unlikely to receive a claim for a thermostat that stuck open as no major down stream damage would be caused. The thermostats that I was involved with had no mechanism to stop the possibility of jamming closed. If the wax pellet was subjected to elevated temperatures firstly the wax carbonised to a runny mush that then leaked past the neoprene pin seal that also failed due to exposure to high temps. The end result was a jammed closed thermostat and some level of engine damage normally would follow. Thank you for explaining the other side of the discussion. I guess in summary try changing the thermostat to improve engine operating temp.
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Old 3 Weeks Ago   #9
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Re: Thermostat opening temp

I could well imagine that scenario, Gary, when a motor does a major overheat from other causes like a blown hose. Thermostat shouldn't ever be the original cause of the overheat. I must "google" it to see what I can find.
Cheers
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Old 2 Weeks Ago   #10
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Re: Thermostat opening temp

most of the failed thermo i,ve seen are poorly maintained cars with rust and scale literally rotting the stat in position ,normally open
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