The Function and Malfunction of the Diesel Thermostat - Page 2

kaiser · 20th January 2012, 22:43

A thinking hat is always required. Even, and perhaps especially so, when you least expect it.

I haven't got a clue about the construction of the Diesel engine, but I can see the picture of the thermostat insert. It is similar to the one used in the V6.

Now the V6 I know very well!

So the way the V6 works is like this.
When engine is cold. Thermostat is closed. Small spring loaded valve is off base, and allows water to flow from pump back into the engine. The water circulates around the inside of the engine, and into the heater, only. The radiator is not used.

As the water heats up, the top disk starts moving down, opening the flow to the radiator, and the small disk starts to move down in unison, starting to close the flow into the block.

At fully open top disk, the thermostat is allowing all the water to flow from the pump directly into the radiator, having, with the small disk, blocked any passage of hot water back in the engine.

What the pump experiences is that it can circulate water. Initially just around the engine, which will assist with a uniform even heating up, and eventually switching to fully circulating into the radiator.

Now, I am going to assume here, and I know I shouldn't do this, but it would be rather strange if the operation of this thermostat is not exactly alike.

If I knew the construction of the fitting area, it would be easy to ascertain.

Mike Noc · 20th January 2012, 22:47

TC from the feel of it I don't think that normal pump pressure will move the disc. So it is more for overtravel when the disc valve has shut but the thermostat needs to open further.

If the system overheats then steam could well force it open if it could escape that way.

Regarding the ball valve I'd say definitely used to bleed air from the system when filling, as the pump isn't self priming, and there is a vertical length of pipe below the thermostat that could airlock if the air can't escape. Once the pipe is filled with coolant pressure from the pump will keep the ball valve closed with the engine running.

Mike

WillyHeckaslike · 20th January 2012, 22:52

Quote:

kaiser: If I knew the construction of the fitting area, it would be easy to ascertain.

Any good, Click?

kaiser · 20th January 2012, 23:02

Quote:

Originally Posted by WillyHeckaslike

Any good, Click?

Thanks, but not really. You would need to see the correlation with the cooling system per se.

If my assumption is right, there will be a connection from the small dish side of the thermostat back into the engine, and from the other end of the thermostat into the cooling radiator. In other words, the casting, piping whatever from the thermostat must have two outlets (plus the one for the heater normally). The one outlet could actually be an inlet, back into the engine, that would be controlled by the small disk.

Excellent pictures btw.

BeeJay55 · 20th January 2012, 23:19

When I read interesting, detailed, threads like these I have to wonder where are the engineers and designers who worked on the 75? Are there none on this forum? Did none of them actually buy the car they designed?

kaiser · 20th January 2012, 23:32

Quote:

Originally Posted by BeeJay55

When I read interesting, detailed, threads like these I have to wonder where are the engineers and designers who worked on the 75? Are there none on this forum? Did none of them actually buy the car they designed?

I know of one involved in the design of the engine. He spent years on a particular item. Yet I can tell you he has not grasped the concept he helped design.
It is frightening but true. That is one of the reasons there is so much mumbo jumbo around certain aspects of maintenance and repair.

Oh, and I see you count has jumped!! Maybe it counts on quality, not quantity ;-))

BeeJay55 · 20th January 2012, 23:35

I suppose the process has to be compartmentalised, because of the complexity. Reminds me of the character in The Hitchhiker's Guide to the Galaxy whose role in designing the Earth, was just to design the Norwegian Fiords, or 'crinkley bits' as he called them.

crofts · 21st January 2012, 04:15

Quote:

Originally Posted by Mike Noc

TC from the feel of it I don't think that normal pump pressure will move the disc. So it is more for overtravel when the disc valve has shut but the thermostat needs to open further.
If the system overheats then steam could well force it open if it could escape that way.
Regarding the ball valve I'd say definitely used to bleed air from the system when filling, as the pump isn't self priming, and there is a vertical length of pipe below the thermostat that could airlock if the air can't escape. Once the pipe is filled with coolant pressure from the pump will keep the ball valve closed with the engine running.Mike

Don't know if it's relevant here but one thing I remember from letures is that a centrfugal pump (which is what all car water pumps are) does not create pressure as such. It just thrashes around in the water until there is no impediment to flow. Completely different to a positive pump

kaiser · 21st January 2012, 06:14

Quote:

Originally Posted by crofts

Don't know if it's relevant here but one thing I remember from letures is that a centrfugal pump (which is what all car water pumps are) does not create pressure as such. It just thrashes around in the water until there is no impediment to flow. Completely different to a positive pump

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.

Mike Noc · 21st January 2012, 07:38

Quote:

Originally Posted by kaiser

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.

Well the smaller disc valve appears to be opening to prevent any increase in both pressure and flow rates when the thermostat is closed and the coolant is only using the smaller heater matrix pipework.

Mike

20th January 2012, 22:47	#12
Mike Noc 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: 11,547 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	TC from the feel of it I don't think that normal pump pressure will move the disc. So it is more for overtravel when the disc valve has shut but the thermostat needs to open further. If the system overheats then steam could well force it open if it could escape that way. Regarding the ball valve I'd say definitely used to bleed air from the system when filling, as the pump isn't self priming, and there is a vertical length of pipe below the thermostat that could airlock if the air can't escape. Once the pipe is filled with coolant pressure from the pump will keep the ball valve closed with the engine running. Mike Last edited by Mike Noc; 20th January 2012 at 22:51..

20th January 2012, 23:19	#15
BeeJay55 Avid contributor Rover 75 Tourer, Connoisseur SE Join Date: Nov 2010 Location: Welshpool Posts: 185 Thanks: 0 Thanked 1 Time in 1 Post	When I read interesting, detailed, threads like these I have to wonder where are the engineers and designers who worked on the 75? Are there none on this forum? Did none of them actually buy the car they designed? __________________ *I’m a dyslexic agnostic with insomnia… I lie awake at night wondering if there really is a dog!*

20th January 2012, 23:35	#17
BeeJay55 Avid contributor Rover 75 Tourer, Connoisseur SE Join Date: Nov 2010 Location: Welshpool Posts: 185 Thanks: 0 Thanked 1 Time in 1 Post	I suppose the process has to be compartmentalised, because of the complexity. Reminds me of the character in The Hitchhiker's Guide to the Galaxy whose role in designing the Earth, was just to design the Norwegian Fiords, or 'crinkley bits' as he called them. __________________ *I’m a dyslexic agnostic with insomnia… I lie awake at night wondering if there really is a dog!*

20th January 2012, 22:43	#11
kaiser This is my second home 75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007 Location: Johannesburg ZA Posts: 6,200 Thanks: 1 Thanked 859 Times in 613 Posts	A thinking hat is always required. Even, and perhaps especially so, when you least expect it. I haven't got a clue about the construction of the Diesel engine, but I can see the picture of the thermostat insert. It is similar to the one used in the V6. Now the V6 I know very well! So the way the V6 works is like this. When engine is cold. Thermostat is closed. Small spring loaded valve is off base, and allows water to flow from pump back into the engine. The water circulates around the inside of the engine, and into the heater, only. The radiator is not used. As the water heats up, the top disk starts moving down, opening the flow to the radiator, and the small disk starts to move down in unison, starting to close the flow into the block. At fully open top disk, the thermostat is allowing all the water to flow from the pump directly into the radiator, having, with the small disk, blocked any passage of hot water back in the engine. What the pump experiences is that it can circulate water. Initially just around the engine, which will assist with a uniform even heating up, and eventually switching to fully circulating into the radiator. Now, I am going to assume here, and I know I shouldn't do this, but it would be rather strange if the operation of this thermostat is not exactly alike. If I knew the construction of the fitting area, it would be easy to ascertain.