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Old 21st January 2012, 09:17   #21
David340R
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The only way to really clarify this is to examine a thermostat and water pump together, but I still believe the the second disk is controlling a pressure relief bypass for the pump allowing water to short circuit straight back from the pump outlet to the inlet when it is open.

Pressure relief valves for oil pumps have been standard practice for decades, but as noted earlier they are positive displacement, so can generate very high pressures. For the water pump the problem is that excessive pressure drop means it "thrashes around in the water" which leads to cavitation (formation of bubbles) which as they collapse generate shock waves which can then cause erosion. This is a known problem with pumps and also propellors on ships etc (this effect is also something that is deliberately exploited in some manufacturing processes, but there the cavitation is usually created by other means!). I guess reducing pressure drop will also save a little power, but I doubt it's a big % of engine losses.
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Old 21st January 2012, 09:23   #22
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Originally Posted by Roverowner View Post
All I can say is that my 2005 tourer (german spec) has done over 100.000 miles on the same stat. The engine warms up very quickly and I have really good heat into the car also quickly. Have the inline mod ready if needed but the car doest need anything doing to it....

Mine is the same, 2005, over 100,000 miles and starts heating the interior after a couple of miles/minutes, even in freezing weather
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Old 21st January 2012, 09:26   #23
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It does create pressure, connect a hose to the outlet, and see the water rise. The higher it rises, the higher the pressure. However, there is a limit to the pressure, and it is rather low, after which it will just trash the water.
Compare that to a positive displacement (gear/piston etc) pump. Here you will have pressure of a nature that the jet can shoot through you hand, or crack a cylinder or bend a conrod!

The thermostat in the Diesel will have nothing to do with pressure would be my thinking.
I would expect the centrifugal pump of this type to be able produce no more than around 0.5 PSI of pressure. This type of pump relies on wide unrestricted flow passages, to pump relatively large volumes. Minimal pressure, but large volumes.
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Old 21st January 2012, 10:07   #24
Mike Noc
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Yes and any increase in pressure would be minimal and of no practical significance. I think David 340R may be right, it could well have more to do with preventing pump cavitation when coolant flow is blocked off from the radiator circuit.


Mike

Last edited by Mike Noc; 21st January 2012 at 11:14..
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Old 21st January 2012, 10:33   #25
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Mike Noc, is that the same stat as shown on Willieheckaslike's assembled photo (pg 2)? Looks similar, but not identical. Think the "W" bracket on the disassembled photo is wrong way round?

In fact the more I look at the disassembled stat, it looks in the wrong order. the black plastic on the left should be far right and the two metal discs/washers should be on the left. If you put it in that order it's just a bog standard stat.

Last edited by blacknwhite; 21st January 2012 at 11:02..
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Old 21st January 2012, 11:06   #26
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Mike Noc, is that the same stat as shown on Willieheckaslike's assembled photo (pg 2)? Looks similar, but not identical. Think the "W" bracket on the disassembled photo is wrong way round?
Yes it is the same stat and well spotted the bracket should be the other way round in the photo at the start of this thread. I'll edit a note in.

Apologies for that but you know how it is.... when I drilled the end out of the rod everything shot off. Just checked and it has been reassembled the correct way.

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Old 21st January 2012, 11:14   #27
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It's just a bog standard stat Mike, nowt mysterious at all. It's not the bracket thats wrong it's the black plastic with shaft and the two metal disc that need to be swopped over.

The larger spring is compressed between the bracket and large metal disc and when the wax spring contracts, the large spring pushes the large disc which pulls the shaft and opens the stat. Simples.
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Old 21st January 2012, 11:22   #28
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Originally Posted by blacknwhite View Post
It's just a bog standard stat Mike, nowt mysterious at all. It's not the bracket thats wrong it's the black plastic with shaft and the two metal disc that need to be swopped over.

The larger spring is compressed between the bracket and large metal disc and when the wax spring contracts, the large spring pushes the large disc which pulls the shaft and opens the stat. Simples.
I'm sure the order of the parts in the photo is correct - the large spring sits between the bracket and the rubber coated stat valve and keeps the valve closed against the radiator outlet pipe.

The smaller spring sits the other side of the bracket and bears against the disc. The 2 discs move as one until the smaller disc hits what it seats against and then the spring will take up any overtravel if the thermostat opens any more.

If you look at my first photo in Willy's link you can see the position of the main spring, but the smaller spring is hidden under the metal disc.

Mike

Last edited by Mike Noc; 21st January 2012 at 11:25..
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Old 21st January 2012, 11:45   #29
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Your right. LOL like your photo I got my description the wrong way round. Still a bog standard stat.

What WOULD be interesting is to look at a duff stat. One of two things would stop it functioning. Either the wax spring no longer functions or the ordinary spring breaks (unlikely). Either way it seem like a big problem for a 2 quid item.
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Old 21st January 2012, 12:30   #30
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I think we're 95% there on this. I've set out a few images to help the orientation of stuff.

This first image is from Rimmer's site showing the stat/housing as it comes.



The next two are Mike's photos with the flow paths



Notice in the photo above how the secondary valve disc appears to have pressure marks where it has seated.



The next is Rimmer's image of the pump swiveled round into the mounted position. We need to understand how the pump works in the block. Are there dividing webs cast into it. I haven't got my mind into this bit. I'm sure it's obvious to some of you.



The next is a combination of stat housing and pump, so we can see how they interface with each other.




This is the pump gasket, showing the port into the block



Here's the gasket roughly in position under the pump



So, the secondary valve closes over the port into the block.


TC

Last edited by T-Cut; 21st January 2012 at 13:59..
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