Suspect failed thermostat

[weasley]

This morning is the first time it has been properly cold (the dash read -4.5°C).  I noticed that it took ages for the coolant temperature to start climbing and when it did it would climb when under load, then fall again when idling or slow-moving.  It eventually reached 'normal' just as I got to work (around 25 minutes of mixed driving) but as I drove slowly along the drive to our offices it started to fall again.  The cabin heater was blowing warm air however.  I have never seen this behaviour in this car, and only ever seen it before with cars that had thermostats on the way out.

 

So, I suspect a failing or failed thermostat.  How easy are they to get at and replace?

[Ryeman]

Never had to, thankfully as the latest systems place it at the engine end of the bottom hose.

If that's the case, best of luck.

[Urrell]

So, I suspect a failing or failed thermostat.  How easy are they to get at and replace?

 

If I remember correctly follow the hose out of the coolant tank for about a foot or two.

[blueR36]

25 minutes is not a long time for a diesel as they are so fuel efficient they generate less heat, your heater being on is taking the heat away from your radiator , they can take up to ten miles to get properly warm, oil temp not just water, even my R36,  3.6 and v6 ( and one of the most  inefficient engines) takes up to 3 miles to get warm at these temps and I leave the heater off till it gets properly warm( OIl temp) I have heated seats so not all bad, with your heater off it will get to temp much quicker . Its amazing just how much your heater does rob your radiator of heat , that's why in an overheating car turning on the heater full helps keep it cool 

[weasley]

I appreciate all that, but I have been driving this very car since new in all sorts of weather and it has never done this before.  It is normally surprisingly quick to get 'up to temperature' and it NEVER drops again after getting there.  I monitored oil temp as well this morning and it behaved as expected (ie, just about reached 90°C before I switched off, as per previous experience).

 

I also have heated seats but sadly the kids in the back don't benefit from them.

[Ryeman]

A temporary blind perhaps.

[weasley]

Again, not something I've needed before.  Also, I'm not bought into these in the UK - if the thermostat is not doing its job then a blind may paper over the cracks but won't fix it.  If the thermostat is working then a blind will make very little difference to how the engine warms up under closed-stat conditions.

 

Driving across the Arctic ice in a truck... yes, I can see it but a chilly commute in Blighty... not so much.

[Ryeman]

Again, not something I've needed before.  Also, I'm not bought into these in the UK - if the thermostat is not doing its job then a blind may paper over the cracks but won't fix it.  If the thermostat is working then a blind will make very little difference to how the engine warms up under closed-stat conditions.

 

Driving across the Arctic ice in a truck... yes, I can see it but a chilly commute in Blighty... not so much.

Just a temporary one till diagnosed/fixed.

[gumdrop]

I had a similar experience but the car was in an exposed position, nose to the cold wind.

A passer bye said feel the bottom hose, I did and it was like a "slushy" so I think the ice

was acting like a valve some times letting the warmer water through other times not.

After that I parked stern to the weather and carried a a small board to block off the radiator

if only travelling a short(ish) journey.

I don't doubt it is your thermostat I just related another possible cause.

[anderson99]

This morning is the first time it has been properly cold (the dash read -4.5°C).  I noticed that it took ages for the coolant temperature to start climbing and when it did it would climb when under load, then fall again when idling or slow-moving.  It eventually reached 'normal' just as I got to work (around 25 minutes of mixed driving) but as I drove slowly along the drive to our offices it started to fall again.  The cabin heater was blowing warm air however.  I have never seen this behaviour in this car, and only ever seen it before with cars that had thermostats on the way out.

 

So, I suspect a failing or failed thermostat.  How easy are they to get at and replace?

Hi, I've noticed mine doing this the last few days when its been cold. I think its normal, also the engine idles at about 1000rpm until the temp gauge shows the engine at its normal temp.

[weasley]

Yes, I noticed the high idle too, but as I said I have never seen the coolant temperature struggle to reach 'normal' and then fall again when idling.

 

Before I rip into the engine I'll monitor it, although this cold snap is scheduled to go away so I may not be able to.

[Smokeyjoe]

+1 for higher idle speed and the last trip out took nearly 30 minutes to get up to normal temperature (about 18 miles). Perhaps you just didn't notice it before?

[Yetiflute]

In these cold conditions I have experienced what you describe. It is not uncommon for my temp gauge to drop from "normal" condition after reaching it when travelling a variable low speeds (town driving) in very cold weather.

[muddyjim]

A passer bye said feel the bottom hose, I did and it was like a "slushy" so I think the ice

was acting like a valve some times letting the warmer water through other times not.

If your coolant is able to freeze, you should get it replaced with a decent anti-freeze mix ASAP. If the coolant should freeze inside the engine, it will wreck it!

Jim

Edited 19 January, 2016 by muddyjim

[gumdrop]

Apparently the exposed bottom hose freezing was "common" the antifreeze

making it slushy, if you cannot squeeze the hose, look for core plugs on the

ends of icicles!

[Robjon]

My previous Roomster (1.9TDI) did this.

 

When 'town driving' in very cold weather, I felt the heater was taking away more heat than the engine could produce.

[Yety]

I've noticed a temperature gauge drop in cold weather when warming up occasionally. The heater takes quiet a bit of heat out of the system, turning the CC off can make the gauge reading rise, and likewise turning it back on makes it drop.

As said, diesels are thermally more efficient that petrol units, so if I can manage I try not to use the heater until the temperature gauge is at or near normal before turning on. If I can't because of say misting, I use the re-circ button until everything gets stabilised, and press auto.

Even re-circ use affects the temperature gauge reading when stationary and idling.

[weasley]

It's definitely not right. I'm pretty switched on to stuff like this and the fact I have noticed it is itself a suggestion something is up. Tonight I drove 4 miles before it even moved at all, which is very unusual. I even thought the sender or gauge had packed in but it slowly came to life eventually.

I'll do some poking and prodding when I get a chance and see what bits are hot or not.

[Ryeman]

Sounds like idle is struggling to maintain cabin heat even with (assuming) a closed thermostat - if that's the case, do as the Scandinavians do and use a temp blind.

(another 40*c day yesterday - can we trade?)

[weasley]

OK, so I have managed to convince myself it is the thermostat - this morning was much 'warmer' (+1.5°C) and it still struggled to warm up and the cabin air was not as warm as usual.  Looking into www.partscats.info I think I have tracked down the right diagram.  It show three possible thermostat housings; two which have a separate thermostat and one which is the housing and thermostat combined.  I have had a quick poke about under the bonnet which has revealed that I need more than a quick poke about under the bonnet to identify the right part because from the top you can't see anything - I'll have to get it up on ramps and get the bottom cover off.

 

It is either the simple thermostat (item 13, called the "coolant regulator"), part number 03G1211113 (with o-ring 0381211119B) or it is item 31, the "coolant regulator housing with thermostat", part number 03L121111AC (o-ring 06B1211119B).  Looks like two simple hex-headed bolts to get it off.

 

Once I've had a proper poke about I'll see if it looks DIYable without significant dismantling and, if so, ordering the parts and some replacement coolant.

 

[BobbyG79]

I used to have a Polo 6N2 GTi that did this.  The temp gauge would only creep up (to about hallway to where it should be) whilst idling, but would drop to the bottom whilst driving.

 

First port of call was to change the temp sender since it was the easier job of the two, but since that made no difference at all I changed the thermostat itself which was, as suspected, stuck open.

Edited 21 January, 2016 by BobbyG79

[Yety]

Would it be that they are alternative thermostat arrangements?

I think you would need to view from both top and bottom as it's pretty crowded lower down. The hoses are short and probably hard to move about in situ. I have looked casually at the hoses and shuddered, as I only remove the lower tray to remove mud and associated muck after running around off road.

[weasley]

Would it be that they are alternative thermostat arrangements?

 

That is my inference, yes.

 

You're right, it is tight in there.  I need to see if I have any working room to get to pipe clips, mounting bolts and so on before deciding whether to do it myself or not.  The last thermostat I did was on a 1987 Rover 216 Vanden Plas - 5 minute job!

[skoda1982]

Mine does this in cold weather i  travel 10 miles to work and it takes at least 6 of them before the needle moves it gets to about 45 deg if i turn the heater off it gets to about 80 deg. i drove last saturday for about an hour and a half town roads it hardly got to operating temp 

[weasley]

OK, so the recent cold snap has brought this back.  I left it last time but this time I am investigating a fix.  The car is going in for a cambelt and water pump change in a couple of weeks, so I asked how much extra to do the 'stat whilst they are in there?  £413.15!!  That is more than the price to do the cambelt!  I have asked them if they have quoted me for a standalone job, rather than an incremental one (seeing as though the coolant has to be dropped out anyway to do the pump and all the covers and many parts will be off of it - I'd have expected a few quid in parts and maybe an extra hour of labour).

 

Let's see how far customer loyalty goes, especially seeing as though they 'owe me one' for previous ****-ups.

 

Going back to the cold weather behaviour, one other factor I have noticed is a significant drop in fuel economy (same happened last winter).  I barely get 500 miles between fills now, whereas I would usually expect at least 550.  Aside from the weather, all other factors remain 'constant' (as constant as driving on open roads can get).