CDTI - low operating temperature?

[Workhorse]

Hi all,

I finally got round to working out the dashboard diagnostics on my 2004 75 diesel so that I could see what was going on with the engine temperature. The temperature gauge has always looked on the low side, but I wasn't sure if that was just the gauge under-reading.

Basically, the temperature initially goes up quite rapidly, which would indicate to me that the thermostat is working as it should at least initially. However, after mixed driving the needle only goes about of a third of the way up the dial, which I now know equates to about 70 degrees, so on the low side.

I'm assuming this means I need to look at my thermostat, but I'm just a bit confused that it's initially picking up temperature fine, but it's not getting to the 90 or so degrees I'd expect to see. Is it a case that it's opening a bit too early?

Any thoughts welcomed!
Thanks all

[T-Cut]

To use a well trodden phrase, they all do that. The cause is almost always due to the way these thermostats deteriorate. They start opening earlier and prevent a normal running temperature to be reached. Diesels run pretty cool anyway, but with a properly operating thermostat, it will reach the 85-90C you want. The most popular/easiest/cheapest fix is the inline stat modification.
Some reading: https://cse.google.com/cse?cx=013872...85.H6tDMLnO4gQ


And the correct brand is important.


TC

[DMGRS]

As TC says, very common - over the years we've been working on perfecting the various solutions thrown around for this problem.

First up, easiest - the inline thermostat in the top hose. We offer a kit for £9.99 that includes instructions, a thermostat we know works well and hose clamps - everything needed - https://www.dmgrs.co.uk/collections/...tat-89-degrees

If you'd rather change the original, we offer a 'V3' thermostat which is designed to avoid the original mode of failure - here: https://www.dmgrs.co.uk/products/r75...evised-version

Finally, I had to do the job myself with the V3 - so I wrote a bit of a guide here including a bit more info on each option, and a How To guide for fitting it:
https://the75andztclub.co.uk/forum/s...d.php?t=164968

[Workhorse]

Okay great, thanks both. I'm about due a big service so I'll add a thermostat to the list. I've seen the inline modification, but I'll probably have the original changed as I know it'll annoy me knowing the faulty one is still there!

[marinabrian]

Originally Posted by Workhorse

Okay great, thanks both. I'm about due a big service so I'll add a thermostat to the list. I've seen the inline modification, but I'll probably have the original changed as I know it'll annoy me knowing the faulty one is still there!

It's a three hour job to change the original, and the new one will go the same way.

Compare that to a fix for less than a tenner and fifteen minutes to carry out, both of my diesels have the Renault 5 thermostat fitted

Brian

[clf]

Originally Posted by marinabrian

It's a three hour job to change the original, and the new one will go the same way.

Compare that to a fix for less than a tenner and fifteen minutes to carry out, both of my diesels have the Renault 5 thermostat fitted

Brian

Wahler 3029.89 fitted 4-5 years ago, and still maintaining 86 degrees without issue now. I am surprised, to be honest. It is a bodge, but such an effective bodge it has to be called a fix really.

[BoroRover]

Originally Posted by marinabrian

It's a three hour job to change the original, and the new one will go the same way.

Compare that to a fix for less than a tenner and fifteen minutes to carry out, both of my diesels have the Renault 5 thermostat fitted

Brian

As ever, sound advice. My diesel was running cool...thermostat. Fifteen minutes after Brian turning up, job done, instant fix, fine ever since. What's not to like ?

[edwardmk]

Originally Posted by marinabrian

The fault isn't caused by a failure of the waxstat element, it is erosion of the valve seat of the housing caused initially by wire draw, and eventually cavitation around the area allowing water to bypass the valve irrespective of the position of the wax element.

Replacement of the original thermostat doesn't address the actual problem, and I would advise against doing so, unless you have to work on something such as coolant pump or upper coolant rail or similar that would necessitate removal of the thermostat housing to do so.

Forget your worries about originality, the original design is flawed, and I wouldn't recommend fitting the R5 in hose 'stat if I didn't think it a good idea, or in fact hadn't had one fitted in my own car for the last 100k miles

By all means fit an original though, you can get into practise for doing the job repeatedly

Brian

Just wondering what ‘wire draw’ is?
More detailed info would be great when you have time


Sent from my iPhone using Tapatalk

[marinabrian]

Originally Posted by edwardmk

Just wondering what ‘wire draw’ is?
More detailed info would be great when you have time


Sent from my iPhone using Tapatalk

Wire drawing is normally caused when the valve closes trapping a hard contaminant between the valve and it's seat, and the subsequent coolant flow then scours a line in the valve seat that allows water to bypass, even when the valve is closed.

Once the process starts, it is self perpetuating cycle of deterioration.

Hope this explains it.

Brian