Why the Discovery 2 "Inline Thermostat" mod is a BAD idea
Thread Starter
|
Banned
Joined: Aug 2021
Posts: 260
Likes: 181
Also, I do realize it was you that did the PCV mod and had the sticky, and IMO, I always thought that was a great mod, and was absolutely NOT the stickies I was referring to. That one is well thought out, a beneficial and honestly necessary improvement over the OE setup.
Happy modding.... from the Azshole
Last edited by RA122125; Jan 31, 2025 at 09:53 PM.
Camel Trophy
Joined: Sep 2017
Posts: 3,820
Likes: 1,337
From: Mission BC Canada
@Mntnceguy
Actually, every thermostat I have used from the 70's on had a "bleed hole" or jiggle pin. The primary reason is to keep air out of the systems, which why the orientation of the hole important in the inline mod it has to be at the the top. When the thermostat was mounted in the block facing up it was not an issue where the hole was.
I know the bleeder holes are less common due to engine design, but rover block is still a 1960's block. At 16 PSI this is a pretty low-pressure cooling system, rads, hoses and heater cores are rated quite a bit higher in the range of 30 to 40 psi on average, you woudl be pissing collant out of teh overflow before you could damage anything, assuming it is not rotted out of course.
Actually, every thermostat I have used from the 70's on had a "bleed hole" or jiggle pin. The primary reason is to keep air out of the systems, which why the orientation of the hole important in the inline mod it has to be at the the top. When the thermostat was mounted in the block facing up it was not an issue where the hole was.
I know the bleeder holes are less common due to engine design, but rover block is still a 1960's block. At 16 PSI this is a pretty low-pressure cooling system, rads, hoses and heater cores are rated quite a bit higher in the range of 30 to 40 psi on average, you woudl be pissing collant out of teh overflow before you could damage anything, assuming it is not rotted out of course.
Rock Crawling
Joined: Nov 2023
Posts: 289
Likes: 104
From: Colorado and New Hampshire
I'm not convinced that you have thoroughly evaluated your own problem. I have it installed in my '03. It lives in NH and above 10,000 ft in the Rockies. I haven't seen the problem you assert nor do I agree that your analysis/list of deficiencies is rock solid. I'm open to learning something new, but right now I'm unconvinced.
Recovery Vehicle
Joined: Dec 2016
Posts: 1,177
Likes: 473
Hmmmmm…. You know I like best about this thread? It has stayed very civil. Remember when I left the D2 world a few years ago? Part of the reason I wanted to come back was the community- and this one in particular.
Why are we all here (on this forum)? In many regards as an escape to the utter ridiculousness of life: the ignorance and hate, the mindless political gibberish, the stress of trying to find something positive in life. We are having fun with what for some is a toy, for others a hobby, or maybe even a first car. The fact we can have discussions and debates about this or that without personal attacks or other typical behaviors in society/social media that create camps of opposing sides, is wonderful and makes me glad I’m still here. When I first read this thread, I thought “Oh great, this forum is now going to become a **** show like all the others”.
Now with my Sunday morning coffee induced philosophizing out of the way, this seems much ado about nothing. In my opinion there are so many other issues to address in the platform, this falls into a “one of” that could be prioritized as an owner sees fit. And I believe there is enough data to support either agreeing or disagreeing with the solution. Lots of variables come into play including climate, use cases, overall condition of the engine, and other aspects of other updates/changes made (water pump, oil viscosity, fan clutch, etc), so an elaborate rabbit hole such as this seems like we’re all kinda bored.
Eh, I’ll be quiet now, but will mention again that I’m happy this has stayed civil.
Why are we all here (on this forum)? In many regards as an escape to the utter ridiculousness of life: the ignorance and hate, the mindless political gibberish, the stress of trying to find something positive in life. We are having fun with what for some is a toy, for others a hobby, or maybe even a first car. The fact we can have discussions and debates about this or that without personal attacks or other typical behaviors in society/social media that create camps of opposing sides, is wonderful and makes me glad I’m still here. When I first read this thread, I thought “Oh great, this forum is now going to become a **** show like all the others”.
Now with my Sunday morning coffee induced philosophizing out of the way, this seems much ado about nothing. In my opinion there are so many other issues to address in the platform, this falls into a “one of” that could be prioritized as an owner sees fit. And I believe there is enough data to support either agreeing or disagreeing with the solution. Lots of variables come into play including climate, use cases, overall condition of the engine, and other aspects of other updates/changes made (water pump, oil viscosity, fan clutch, etc), so an elaborate rabbit hole such as this seems like we’re all kinda bored.
Eh, I’ll be quiet now, but will mention again that I’m happy this has stayed civil.
We all know the inline has to have a bleed hole in the thermostat for multiple reasons on the D2, one of which is so that it doesn't suck itself into a vacuum, no? That thought makes me curious how you can interpret that as no added back pressure, and no other pressures being applied to the wrong places?
Also, I do realize it was you that did the PCV mod and had the sticky, and IMO, I always thought that was a great mod, and was absolutely NOT the stickies I was referring to. That one is well thought out, a beneficial and honestly necessary improvement over the OE setup.
Happy modding.... from the Azshole
Also, I do realize it was you that did the PCV mod and had the sticky, and IMO, I always thought that was a great mod, and was absolutely NOT the stickies I was referring to. That one is well thought out, a beneficial and honestly necessary improvement over the OE setup.
Happy modding.... from the Azshole
Drifting
Joined: Oct 2022
Posts: 40
Likes: 19
Jiggle oins close the hole, once coolant is flowing to prevent the flow through the hole.
I fitted an aftermarket thermostat design to my wifes old BMW, which the "designer" drilled a hole in the flange, to help bleed air. It took a VERY long time to heat up around town, and the fuel consumption during commuting increase about 20%. I changed to the un-drilled version and the problems disappeared. If had a built in bleed anyway.
You don't want a hole, as the flow DOES cool the engine, when you least want it.
The original design is supposed to work by circulating water continually through the block, even when cold. It gives even warming of the engine and also faster/smoother feedback to the thermostat. The other feature of the original system, is that when the thermostat is wide open, it actually FORCES the water pump to create full flow through the radiator. The inline mod prevents this (as does the standard D1 system), and the description you tube video of how the D2 system works I've seen posted on this forum, is incorrect in a few ways. The water pump does not create any pressure to push on springs etc - actually the pump doesn't create any real pressure at all - it's just a circulator, not a pump. That spring in the original thermostat is to allow the plate on the back of the thermostat to STOP the coolant recirculatiing and force it through the radiator circuit; the spring allows the thermostat to fully open, after that port is closed.
It's how most modern cooling systems work, and is the type of system, where removing the thermostat can actually CAUSE opverheating as the hot coolant can circulate within the block and not be forced to the radiator. The D1 does it to a certain degree, through the heater system, but it's a much smaller flow path, so flow is generally somewhat diverted to the radiator circuit, although it often require raised RPM for the pump to get the water moving well enough.
Description here - this is a basic explanation of how the D2 system works (the same as most modern systems), with the block-off to force full circulation through the radiator - it should work like that, all being well:
I fitted an aftermarket thermostat design to my wifes old BMW, which the "designer" drilled a hole in the flange, to help bleed air. It took a VERY long time to heat up around town, and the fuel consumption during commuting increase about 20%. I changed to the un-drilled version and the problems disappeared. If had a built in bleed anyway.
You don't want a hole, as the flow DOES cool the engine, when you least want it.
The original design is supposed to work by circulating water continually through the block, even when cold. It gives even warming of the engine and also faster/smoother feedback to the thermostat. The other feature of the original system, is that when the thermostat is wide open, it actually FORCES the water pump to create full flow through the radiator. The inline mod prevents this (as does the standard D1 system), and the description you tube video of how the D2 system works I've seen posted on this forum, is incorrect in a few ways. The water pump does not create any pressure to push on springs etc - actually the pump doesn't create any real pressure at all - it's just a circulator, not a pump. That spring in the original thermostat is to allow the plate on the back of the thermostat to STOP the coolant recirculatiing and force it through the radiator circuit; the spring allows the thermostat to fully open, after that port is closed.
It's how most modern cooling systems work, and is the type of system, where removing the thermostat can actually CAUSE opverheating as the hot coolant can circulate within the block and not be forced to the radiator. The D1 does it to a certain degree, through the heater system, but it's a much smaller flow path, so flow is generally somewhat diverted to the radiator circuit, although it often require raised RPM for the pump to get the water moving well enough.
Description here - this is a basic explanation of how the D2 system works (the same as most modern systems), with the block-off to force full circulation through the radiator - it should work like that, all being well:
Drifting
Joined: Jan 2025
Posts: 26
Likes: 5
Jiggle oins close the hole, once coolant is flowing to prevent the flow through the hole.
I fitted an aftermarket thermostat design to my wifes old BMW, which the "designer" drilled a hole in the flange, to help bleed air. It took a VERY long time to heat up around town, and the fuel consumption during commuting increase about 20%. I changed to the un-drilled version and the problems disappeared. If had a built in bleed anyway.
You don't want a hole, as the flow DOES cool the engine, when you least want it.
The original design is supposed to work by circulating water continually through the block, even when cold. It gives even warming of the engine and also faster/smoother feedback to the thermostat. The other feature of the original system, is that when the thermostat is wide open, it actually FORCES the water pump to create full flow through the radiator. The inline mod prevents this (as does the standard D1 system), and the description you tube video of how the D2 system works I've seen posted on this forum, is incorrect in a few ways. The water pump does not create any pressure to push on springs etc - actually the pump doesn't create any real pressure at all - it's just a circulator, not a pump. That spring in the original thermostat is to allow the plate on the back of the thermostat to STOP the coolant recirculatiing and force it through the radiator circuit; the spring allows the thermostat to fully open, after that port is closed.
It's how most modern cooling systems work, and is the type of system, where removing the thermostat can actually CAUSE opverheating as the hot coolant can circulate within the block and not be forced to the radiator. The D1 does it to a certain degree, through the heater system, but it's a much smaller flow path, so flow is generally somewhat diverted to the radiator circuit, although it often require raised RPM for the pump to get the water moving well enough.
Description here - this is a basic explanation of how the D2 system works (the same as most modern systems), with the block-off to force full circulation through the radiator - it should work like that, all being well:
https://youtu.be/k0ovUHEOtyE?si=raq7wfJbJhv89lrx&t=279
I fitted an aftermarket thermostat design to my wifes old BMW, which the "designer" drilled a hole in the flange, to help bleed air. It took a VERY long time to heat up around town, and the fuel consumption during commuting increase about 20%. I changed to the un-drilled version and the problems disappeared. If had a built in bleed anyway.
You don't want a hole, as the flow DOES cool the engine, when you least want it.
The original design is supposed to work by circulating water continually through the block, even when cold. It gives even warming of the engine and also faster/smoother feedback to the thermostat. The other feature of the original system, is that when the thermostat is wide open, it actually FORCES the water pump to create full flow through the radiator. The inline mod prevents this (as does the standard D1 system), and the description you tube video of how the D2 system works I've seen posted on this forum, is incorrect in a few ways. The water pump does not create any pressure to push on springs etc - actually the pump doesn't create any real pressure at all - it's just a circulator, not a pump. That spring in the original thermostat is to allow the plate on the back of the thermostat to STOP the coolant recirculatiing and force it through the radiator circuit; the spring allows the thermostat to fully open, after that port is closed.
It's how most modern cooling systems work, and is the type of system, where removing the thermostat can actually CAUSE opverheating as the hot coolant can circulate within the block and not be forced to the radiator. The D1 does it to a certain degree, through the heater system, but it's a much smaller flow path, so flow is generally somewhat diverted to the radiator circuit, although it often require raised RPM for the pump to get the water moving well enough.
Description here - this is a basic explanation of how the D2 system works (the same as most modern systems), with the block-off to force full circulation through the radiator - it should work like that, all being well:
https://youtu.be/k0ovUHEOtyE?si=raq7wfJbJhv89lrx&t=279
Camel Trophy
Joined: Sep 2017
Posts: 3,820
Likes: 1,337
From: Mission BC Canada
@AlWorms That is a explanation of a modern cooling system, and the later D2 system, and actually explains it really well. But the reality is the Rover V8 is a very old engine design. Dropping the original D2 thermostat for a D1 style location does not really create anymore issues, it is just a simpler flow path which was used on the engine for 40 odd years. The new cooling systems would actually have been fine except, BMW/Rover did not improve the cooling pump or increase the radiator size. Adding a temp gauge that is an idiot light did not help either. And of course to compound the issue most of the aftermarket original D2 design thermostats have terrible quality control leading to a high failure rate, higher than indicated opening temps etc.
Yep most "aftermarket" OEM style thermostats are NOT 180F units. The first batch of black Britpart 180's were actually 178F's and when they changed distributors = those immediately were marked 180F but where actually 190/195F thermostats! I only trust an OEM LR grey diesel 180F OEM style thermostat.
Yep fact is this engine ran fine on the normal standard coolant design for 40 years vs the BMW 99-04 stuff which has the worse reputation out of all the LR Discovery years. Increased engine temps for emissions, old tooling to make the blocks, and a company just trying to get the last Discovery off the line so LR3/RRS production could roll out.
I have owned more D1's now vs D2's (count is scary how many LR's have gone thru my fingers that I've brought back from the dead!). The D1 cooling system is simple, and more robust. D2 is plagued with BMW plastics that will fail no questions about it (I replace or mod as much of that crap as I can).
A D1/D2 can see temps up to 225/229F if pushed with ZERO damage as long as the system is in top shape. 99-04 D2's were pushing this right off the line for years n years. You can have a spike, as long as it goes up and tops out and goes back down. If you hit 225F then you see 230+ = SHUT DOWN, but if you see 220-226F and it goes back down say out on a trail and you move in 4lo and the fan clutch kicks in the temps will drop back down as low as 188F.
I honestly just don't chance it anymore. If I get stuck in a wreck or traffic and temps climb I just pull off n shut down or stop for a coffee. Rather waste an hour vs ruin a perfect running engine boiling it to death.
Thats when a constant high power efan would be key vs the fan clutch for that situation. My D1's I have a HDC switch in the ac efan circuit. If out on the trail I can engage the switch and run my efans without the AC on. It helps out a lot out on the trail or traffic!!
Our D1/D2's have a very small radiator footprint/grill. H3 Alpha I owned acted the same way! Inline vs OEM can just be a tie as way to many other factors are at play honestly.
Yep fact is this engine ran fine on the normal standard coolant design for 40 years vs the BMW 99-04 stuff which has the worse reputation out of all the LR Discovery years. Increased engine temps for emissions, old tooling to make the blocks, and a company just trying to get the last Discovery off the line so LR3/RRS production could roll out.
I have owned more D1's now vs D2's (count is scary how many LR's have gone thru my fingers that I've brought back from the dead!). The D1 cooling system is simple, and more robust. D2 is plagued with BMW plastics that will fail no questions about it (I replace or mod as much of that crap as I can).
A D1/D2 can see temps up to 225/229F if pushed with ZERO damage as long as the system is in top shape. 99-04 D2's were pushing this right off the line for years n years. You can have a spike, as long as it goes up and tops out and goes back down. If you hit 225F then you see 230+ = SHUT DOWN, but if you see 220-226F and it goes back down say out on a trail and you move in 4lo and the fan clutch kicks in the temps will drop back down as low as 188F.
I honestly just don't chance it anymore. If I get stuck in a wreck or traffic and temps climb I just pull off n shut down or stop for a coffee. Rather waste an hour vs ruin a perfect running engine boiling it to death.
Thats when a constant high power efan would be key vs the fan clutch for that situation. My D1's I have a HDC switch in the ac efan circuit. If out on the trail I can engage the switch and run my efans without the AC on. It helps out a lot out on the trail or traffic!!
Our D1/D2's have a very small radiator footprint/grill. H3 Alpha I owned acted the same way! Inline vs OEM can just be a tie as way to many other factors are at play honestly.
Drifting
Joined: Jan 2025
Posts: 26
Likes: 5
Yep most "aftermarket" OEM style thermostats are NOT 180F units. The first batch of black Britpart 180's were actually 178F's and when they changed distributors = those immediately were marked 180F but where actually 190/195F thermostats! I only trust an OEM LR grey diesel 180F OEM style thermostat.
Yep fact is this engine ran fine on the normal standard coolant design for 40 years vs the BMW 99-04 stuff which has the worse reputation out of all the LR Discovery years. Increased engine temps for emissions, old tooling to make the blocks, and a company just trying to get the last Discovery off the line so LR3/RRS production could roll out.
I have owned more D1's now vs D2's (count is scary how many LR's have gone thru my fingers that I've brought back from the dead!). The D1 cooling system is simple, and more robust. D2 is plagued with BMW plastics that will fail no questions about it (I replace or mod as much of that crap as I can).
A D1/D2 can see temps up to 225/229F if pushed with ZERO damage as long as the system is in top shape. 99-04 D2's were pushing this right off the line for years n years. You can have a spike, as long as it goes up and tops out and goes back down. If you hit 225F then you see 230+ = SHUT DOWN, but if you see 220-226F and it goes back down say out on a trail and you move in 4lo and the fan clutch kicks in the temps will drop back down as low as 188F.
I honestly just don't chance it anymore. If I get stuck in a wreck or traffic and temps climb I just pull off n shut down or stop for a coffee. Rather waste an hour vs ruin a perfect running engine boiling it to death.
Thats when a constant high power efan would be key vs the fan clutch for that situation. My D1's I have a HDC switch in the ac efan circuit. If out on the trail I can engage the switch and run my efans without the AC on. It helps out a lot out on the trail or traffic!!
Our D1/D2's have a very small radiator footprint/grill. H3 Alpha I owned acted the same way! Inline vs OEM can just be a tie as way to many other factors are at play honestly.
Yep fact is this engine ran fine on the normal standard coolant design for 40 years vs the BMW 99-04 stuff which has the worse reputation out of all the LR Discovery years. Increased engine temps for emissions, old tooling to make the blocks, and a company just trying to get the last Discovery off the line so LR3/RRS production could roll out.
I have owned more D1's now vs D2's (count is scary how many LR's have gone thru my fingers that I've brought back from the dead!). The D1 cooling system is simple, and more robust. D2 is plagued with BMW plastics that will fail no questions about it (I replace or mod as much of that crap as I can).
A D1/D2 can see temps up to 225/229F if pushed with ZERO damage as long as the system is in top shape. 99-04 D2's were pushing this right off the line for years n years. You can have a spike, as long as it goes up and tops out and goes back down. If you hit 225F then you see 230+ = SHUT DOWN, but if you see 220-226F and it goes back down say out on a trail and you move in 4lo and the fan clutch kicks in the temps will drop back down as low as 188F.
I honestly just don't chance it anymore. If I get stuck in a wreck or traffic and temps climb I just pull off n shut down or stop for a coffee. Rather waste an hour vs ruin a perfect running engine boiling it to death.
Thats when a constant high power efan would be key vs the fan clutch for that situation. My D1's I have a HDC switch in the ac efan circuit. If out on the trail I can engage the switch and run my efans without the AC on. It helps out a lot out on the trail or traffic!!
Our D1/D2's have a very small radiator footprint/grill. H3 Alpha I owned acted the same way! Inline vs OEM can just be a tie as way to many other factors are at play honestly.
