|
||
|
21st January 2012, 08:17 | #21 |
Avid contributor
MG ZT-T Join Date: Dec 2010
Location: Leics
Posts: 141
Thanks: 2
Thanked 4 Times in 4 Posts
|
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. |
21st January 2012, 08:23 | #22 | |
Posted a thing or two
Rover 75 Conn SE Tourer Join Date: Aug 2011
Location: Driffield
Posts: 1,952
Thanks: 27
Thanked 151 Times in 125 Posts
|
Quote:
Mine is the same, 2005, over 100,000 miles and starts heating the interior after a couple of miles/minutes, even in freezing weather |
|
21st January 2012, 08:26 | #23 | |
This is my second home
75 Contemporary SE Mk II 2004 Man. Sal. CDTi 135ps, FBH on red diesel, WinCE6 DD Join Date: May 2010
Location: Leeds
Posts: 17,273
Thanks: 2,160
Thanked 2,061 Times in 1,586 Posts
|
Quote:
__________________
Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money. |
|
21st January 2012, 09:07 | #24 |
This is my second home
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009
Location: Hampshire
Posts: 11,569
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
|
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 10:14.. |
21st January 2012, 09:33 | #25 |
Posted a thing or two
Black Rover 75 Connie CDT and Twilight Chromactive ZT Turbo Join Date: Jun 2011
Location: Newcastle upon Tyne
Posts: 1,602
Thanks: 15
Thanked 16 Times in 7 Posts
|
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 10:02.. |
21st January 2012, 10:06 | #26 | |
This is my second home
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009
Location: Hampshire
Posts: 11,569
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
|
Quote:
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. Mike |
|
21st January 2012, 10:14 | #27 |
Posted a thing or two
Black Rover 75 Connie CDT and Twilight Chromactive ZT Turbo Join Date: Jun 2011
Location: Newcastle upon Tyne
Posts: 1,602
Thanks: 15
Thanked 16 Times in 7 Posts
|
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. |
21st January 2012, 10:22 | #28 | |
This is my second home
Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009
Location: Hampshire
Posts: 11,569
Thanks: 3,470
Thanked 3,119 Times in 2,247 Posts
|
Quote:
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 10:25.. |
|
21st January 2012, 10:45 | #29 |
Posted a thing or two
Black Rover 75 Connie CDT and Twilight Chromactive ZT Turbo Join Date: Jun 2011
Location: Newcastle upon Tyne
Posts: 1,602
Thanks: 15
Thanked 16 Times in 7 Posts
|
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. |
21st January 2012, 11:30 | #30 |
This is my second home
Rover75 and Mreg Corsa. Join Date: Nov 2006
Location: Sumweer onat mote o'dust (Sagin)
Posts: 21,753
Thanks: 341
Thanked 3,660 Times in 2,924 Posts
|
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 12:59.. |
|
|