Faulty Thermostat on Rover 75 CDT?

KeirL · 18th September 2016, 13:48

Hello

I’m trying to diagnose if the thermostat on my 2005 Rover 75 CDT is stuck open. Here are the symptoms and what I’ve tried so far to diagnose the issue:
I’ve had the car for a number of years and the temp gauge has generally stayed at 9 o’clock 99% of the time
Over the last 6 – 12 months I’ve noticed the needle quite regularly moving between 8 – 9 o’clock position – I’ve kind of noted this but ignored it as an issue. It’s never gone above the 9 o’clock position
Over the last few days the needle has never really moved higher than the 8 o’clock position but can just about reach the 9 o’clock position if I’m travelling slowly or sitting in traffic. Again it has never climbed any higher
If I’m on open roads (especially on free flowing motorways – yes there are such things!) then it sometimes barely gets past the blue.
I’ve never heard the fans cut in once
I thought it time to take a closer look at this and so here’s what I’ve tried:
Removed all the coolant from the rad and block (removed top and bottom rad hoses and block drain plug). The coolant was in good shape and mostly clean – the antifreeze was replaced about 2 years ago. I would say about 7 – 8 litres came out. Also flushed the rad through with a hose until it ran clear.
Removed and cleaned temp sensor connector and pushed back on
Refilled with 4 litres of new antifreeze and topped up with water – again about 8 litres added in total and bled system. Went for a drive, checked levels and topped up.
Temp gauge still not getting past the 8 o’clock position. Stopped the car and opened the bonnet – engine temp ‘felt and smelt’ normal. Top hose was hot and I was able to open the expansion tank with very little hiss and water temp was ok to touch.
The heater blows out ‘hot’ when on Hi and I would judge that the heat is a little lower when the temp gauge is below the 8 o’clock position but it is still ‘warm’ and has never blown cold.
Started the car and setup the diagnostics to display the water temp (setting 7.0) and went for a drive. Temp diagnostics followed behaviour of the temp gauge (I’m not sure if it uses the same sensor?). As the gauge fluctuated up and down so did the digital read out from the diagnsotics. The highest it showed during normal driving was 68 degrees. Ocassionally touching the low 70’s if I stopped at traffic lights. The needle never really went past the 8 o’clock position.
Got back home and stopped in the driveway with the engine running at about 2000 revs for about 5mins. I managed to get the temp needle to move up to (just below) the 9 o’clock position and the diagnostics showed 72 degrees. I continued for a further few minutes and the diagnostics temp moved up to 85 degrees whereas the needle didn’t move. When I got to 85 degrees I turned of the engine – but I suspect the diagnostic readings would have increased further – at no time did the fans come on.
It seems to me to be a themostat stuck open as there’s nothing else that feels to be happening other than the water just isn’t getting up to temperature. On open roads with fast air passing through the rad it’s just cooling the water temp significantly.
I’ve can’t say I’ve noticed if the car has been taking longer and longer to get up to temp over the last 12 months but I guess it could have been. And I can’t really say I’ve noticed any drop in mpg – it’s doing around 45mpg and that’s all it’s done as far as I can remember.
I’m keen to understand if there are any further tests I can do to narrow it down any further and also if there are an short or long term concerns that I should worry about. I guess with the weather being good for the last few months (generally) then I haven’t seen any major adverse affects. This may change if we have a cold snap as we head into winter. So I’d rather get this sorted over the coming weeks.
I guess I could go for the ‘inline’ thermostat mod to help confirm the issue and perhaps leave that in as a permanent fix? But would be a little concerned that if the thermostat is stuck open then perhaps it could get stuck closed and I’d be in all kind of problems then – so would fix the existing thermostat than just fit an inline one.
I appreciate this is a long post and thanks for your perseverance in reading it, but I wanted to add as much detail as possible…… still happy to answer any questions that I may not have included here.
Thanks again - Keir

clf · 18th September 2016, 14:36

Firstly use the gauge as a guide only, and a very very rough one at that. (I believe 9o'clock position represents between 75 and 100 degrees!). The thermostat is unlikely to be stuck open. The general consensus is that it opens early.

If you do insert an inline thermostat (the Renault 5 version), make sure the cup is watertight. If it isnt, the engine will take an age to warm up.

The ideal solution is replacement of the original thermostat, version 3 as sold by DMGRS is reported to be very reliable. But it does require a lot of effort to fit. Well certainly a lot more than the R5 or the inline housing. I would suggest inserting the R5 as it is relatively cheap, and very easy. It will make an immediate difference, allowing you to enjoy the benefits of engine being up to temp quite quickly, whilst deciding to live with it or replacing the original.

One thing, if you do replace the original, any inline stat fitted MUST be removed.

Some links

CDTi Thermostats - Why they fail, how to diagnose yours and how to fix by Mat at DMGRS

the forum Google search is your friend

Watertight Video

Leaking

opening test prior to fitting

my videos on the thermostat

T-Cut · 18th September 2016, 21:13

Quote:

Originally Posted by KeirL

I guess I could go for the ‘inline’ thermostat mod to help confirm the issue and perhaps leave that in as a permanent fix? But would be a little concerned that if the thermostat is stuck open then perhaps it could get stuck closed and I’d be in all kind of problems then – so would fix the existing thermostat than just fit an inline one.

Everything you've described is in the text book of evidence that the 'mk2' thermostat design fitted to diesels begins to fail in a rather odd way. It starts opening earlier and earlier. In other words, at lower and lower temperatures. They never ever 'fail shut' nor do they 'fail open'. They simply cause lower and lower running temperatures, opening and closing as they do.

The reason why this happens was determined a few years ago and is informative reading for anyone really interested and with a few hours to spend on the topic. This is what you want:

The Function and Malfunction of the Diesel Thermostat http://www.the75andztclub.co.uk/foru...d.php?t=102943

So basically, you have classic thermostat syndrome and you have two options. Replace the old stat/housing with the later (so called Mk3) version or save a lot of money/effort and add the in-line thermostat. You can get the Mk3 version from DMGRS here on the forum, or buy a Renault 5 in-line 89°C type and stick itin the top hose. Either strategy will bring the running temperature into the sweet zone close to 90°C. The engine will suffer no ill effects which ever way you go. It's suffering as it is at present.

EDIT: Yes I forgot, there are only two or three in-line stat brands that do a good job. See clf's watertight video above.

TC

KeirL · 19th September 2016, 14:27

Brilliant - thanks guys
I'll get one of the R5 stats ordered from DMGRS and keep things simple.

cheers

Stevie Boy · 3rd December 2018, 18:17

Recently purchased a 2002 Connoisseur SE CDT. Does seem to run very cool. Just been on a 15 mile drive. Temp gauge went to the 9 o'clock position fairly quickly but for the entire drive highest temp was 87 degrees. Roads were a mixture of motorway and national speed limit roads and it is a chilly December evening (about 6 degrees air temp ) and i was in clear air pretty much the whole time but that sound right?

I suspect not as sat on my drive for 5 mins after with engine on and still never went past 87..

KeithA · 3rd December 2018, 19:16

Quote:

Originally Posted by Stevie Boy

Recently purchased a 2002 Connoisseur SE CDT. Does seem to run very cool. Just been on a 15 mile drive. Temp gauge went to the 9 o'clock position fairly quickly but for the entire drive highest temp was 87 degrees. Roads were a mixture of motorway and national speed limit roads and it is a chilly December evening (about 6 degrees air temp ) and i was in clear air pretty much the whole time but that sound right?

I suspect not as sat on my drive for 5 mins after with engine on and still never went past 87..

That's actually pretty good!

Sent from my Redmi 5 Plus using Tapatalk

75driver · 3rd December 2018, 19:45

I think I would be happy with that.😄

Sent from my iPhone using Tapatalk

Stevie Boy · 3rd December 2018, 19:47

Quote:

Originally Posted by KeithA

That's actually pretty good!

Sent from my Redmi 5 Plus using Tapatalk

So that's normal then?

bl52krz · 3rd December 2018, 19:52

An 88 deg thermostat is fitted from new. So yours is working ok.

Stevie Boy · 3rd December 2018, 20:04

Quote:

Originally Posted by bl52krz

An 88 deg thermostat is fitted from new. So yours is working ok.

Great. Used to my 1.8T i had previously that used to run hotter

18th September 2016, 13:48	#1
KeirL Regular poster Rover 75 Tourer Join Date: Apr 2008 Location: Beckley Posts: 54 Thanks: 4 Thanked 11 Times in 5 Posts	Faulty Thermostat on Rover 75 CDT? Hello I’m trying to diagnose if the thermostat on my 2005 Rover 75 CDT is stuck open. Here are the symptoms and what I’ve tried so far to diagnose the issue: I’ve had the car for a number of years and the temp gauge has generally stayed at 9 o’clock 99% of the time Over the last 6 – 12 months I’ve noticed the needle quite regularly moving between 8 – 9 o’clock position – I’ve kind of noted this but ignored it as an issue. It’s never gone above the 9 o’clock position Over the last few days the needle has never really moved higher than the 8 o’clock position but can just about reach the 9 o’clock position if I’m travelling slowly or sitting in traffic. Again it has never climbed any higher If I’m on open roads (especially on free flowing motorways – yes there are such things!) then it sometimes barely gets past the blue. I’ve never heard the fans cut in once I thought it time to take a closer look at this and so here’s what I’ve tried: Removed all the coolant from the rad and block (removed top and bottom rad hoses and block drain plug). The coolant was in good shape and mostly clean – the antifreeze was replaced about 2 years ago. I would say about 7 – 8 litres came out. Also flushed the rad through with a hose until it ran clear. Removed and cleaned temp sensor connector and pushed back on Refilled with 4 litres of new antifreeze and topped up with water – again about 8 litres added in total and bled system. Went for a drive, checked levels and topped up. Temp gauge still not getting past the 8 o’clock position. Stopped the car and opened the bonnet – engine temp ‘felt and smelt’ normal. Top hose was hot and I was able to open the expansion tank with very little hiss and water temp was ok to touch. The heater blows out ‘hot’ when on Hi and I would judge that the heat is a little lower when the temp gauge is below the 8 o’clock position but it is still ‘warm’ and has never blown cold. Started the car and setup the diagnostics to display the water temp (setting 7.0) and went for a drive. Temp diagnostics followed behaviour of the temp gauge (I’m not sure if it uses the same sensor?). As the gauge fluctuated up and down so did the digital read out from the diagnsotics. The highest it showed during normal driving was 68 degrees. Ocassionally touching the low 70’s if I stopped at traffic lights. The needle never really went past the 8 o’clock position. Got back home and stopped in the driveway with the engine running at about 2000 revs for about 5mins. I managed to get the temp needle to move up to (just below) the 9 o’clock position and the diagnostics showed 72 degrees. I continued for a further few minutes and the diagnostics temp moved up to 85 degrees whereas the needle didn’t move. When I got to 85 degrees I turned of the engine – but I suspect the diagnostic readings would have increased further – at no time did the fans come on. It seems to me to be a themostat stuck open as there’s nothing else that feels to be happening other than the water just isn’t getting up to temperature. On open roads with fast air passing through the rad it’s just cooling the water temp significantly. I’ve can’t say I’ve noticed if the car has been taking longer and longer to get up to temp over the last 12 months but I guess it could have been. And I can’t really say I’ve noticed any drop in mpg – it’s doing around 45mpg and that’s all it’s done as far as I can remember. I’m keen to understand if there are any further tests I can do to narrow it down any further and also if there are an short or long term concerns that I should worry about. I guess with the weather being good for the last few months (generally) then I haven’t seen any major adverse affects. This may change if we have a cold snap as we head into winter. So I’d rather get this sorted over the coming weeks. I guess I could go for the ‘inline’ thermostat mod to help confirm the issue and perhaps leave that in as a permanent fix? But would be a little concerned that if the thermostat is stuck open then perhaps it could get stuck closed and I’d be in all kind of problems then – so would fix the existing thermostat than just fit an inline one. I appreciate this is a long post and thanks for your perseverance in reading it, but I wanted to add as much detail as possible…… still happy to answer any questions that I may not have included here. Thanks again - Keir

18th September 2016, 14:36	#2
clf This is my second home MG ZT CDTi Join Date: Jan 2014 Location: carrick Posts: 7,859 Thanks: 3,494 Thanked 2,657 Times in 1,973 Posts	Firstly use the gauge as a guide only, and a very very rough one at that. (I believe 9o'clock position represents between 75 and 100 degrees!). The thermostat is unlikely to be stuck open. The general consensus is that it opens early. If you do insert an inline thermostat (the Renault 5 version), make sure the cup is watertight. If it isnt, the engine will take an age to warm up. The ideal solution is replacement of the original thermostat, version 3 as sold by DMGRS is reported to be very reliable. But it does require a lot of effort to fit. Well certainly a lot more than the R5 or the inline housing. I would suggest inserting the R5 as it is relatively cheap, and very easy. It will make an immediate difference, allowing you to enjoy the benefits of engine being up to temp quite quickly, whilst deciding to live with it or replacing the original. One thing, if you do replace the original, any inline stat fitted MUST be removed. Some links CDTi Thermostats - Why they fail, how to diagnose yours and how to fix by Mat at DMGRS the forum Google search is your friend Watertight Video Leaking opening test prior to fitting my videos on the thermostat __________________ It is not gloss primer .............. it is duct tape silver! Last edited by clf; 18th September 2016 at 14:45..

3rd December 2018, 19:45	#7
75driver Posted a thing or two Rover 75 saloon, manual. Rover 75 Tourer, Auto. Join Date: Jan 2013 Location: Newry Posts: 1,781 Thanks: 574 Thanked 443 Times in 371 Posts	I think I would be happy with that.😄 Sent from my iPhone using Tapatalk __________________ 2006 75 Contemporary SE diesel manual (#1) 2003 75T Connoisseur SE diesel auto (For Comfort) 2005 75 Connoisseur SE diesel auto (Marmite duotone ) 2006 75 Connoisseur SE diesel auto (The last one?) 2009 E220 (For a change) 2018 L200 (For Big & Heavy Things) 1976 W114 250 Manual (For Sundays)

3rd December 2018, 19:52	#9
bl52krz This is my second home Rover 75 cdt club + Rover 2.5 KV6 Conni SE Join Date: May 2008 Location: Birmingham Posts: 11,387 Thanks: 6,587 Thanked 2,262 Times in 1,729 Posts	An 88 deg thermostat is fitted from new. So yours is working ok. __________________ Great Barr, Birmingham.

19th September 2016, 14:27	#4
KeirL Regular poster Rover 75 Tourer Join Date: Apr 2008 Location: Beckley Posts: 54 Thanks: 4 Thanked 11 Times in 5 Posts	Brilliant - thanks guys I'll get one of the R5 stats ordered from DMGRS and keep things simple. cheers

3rd December 2018, 18:17	#5
Stevie Boy Regular poster Rover 75 Saloon Join Date: Mar 2014 Location: Derby Posts: 96 Thanks: 26 Thanked 33 Times in 11 Posts	Recently purchased a 2002 Connoisseur SE CDT. Does seem to run very cool. Just been on a 15 mile drive. Temp gauge went to the 9 o'clock position fairly quickly but for the entire drive highest temp was 87 degrees. Roads were a mixture of motorway and national speed limit roads and it is a chilly December evening (about 6 degrees air temp ) and i was in clear air pretty much the whole time but that sound right? I suspect not as sat on my drive for 5 mins after with engine on and still never went past 87..