Citroen XM Forum

Posted: **Tue Aug 17, 2010 11:09 am**

A fella on FrenchCarForum is deliberately setting his Xantia 2.0i 16v engine up
to run at a significantly reduced operating temperature of half of thereabouts -
probably primarily through removal of the thermostat. He cites using decent
oil as a fix for the potential higher wear and tear on the engine and the plan
is to keep the engine going for 10 years with high miles.

http://www.frenchcarforum.co.uk/forum/v ... 755#234755

FWIW this is my reply on the thread:

If most of the wear and tear on engines is caused in the first 5 minutes
after start up while it warms up, it never will on your 2.0i 16v and the
engine will be a wreck in no time/miles.

I've come across this idea before as one of my Cx turbos had it's
thermostat removed and the car would run harder with the fuel
injection effectively running richer ALL THE TIME like it does when
the car is first started - ultimately this did cause issues with the
fuel injection and it would break down and barely idle.

Now I don't even pretend to be an expert in this subject and would
love to see a mechanical engineer weigh into this discussion but looking
extensively through references online, consequences of forced cold
running range from:

• Increased engine wear and corrosion due to a greater concentration
of combustion acids, poorly fitting parts and excess fuel and water
(condensation) in the oil.

• Greatly increased fuel consumption due to car running in cold running
mode with elevated injection phase/pulse width and incorrect operation
of engine management and 02 sensors

• Greatly increased emissions and damage to the catalytic converter
due to the incomplete combustion of fuel

Basically, engines need to be warm so all internal components are expanded
to operational sizes, and combustion takes place properly. Just using more
expensive oil isn't the full remedy to this. You've got to rationalise that the
optimum operating point the engine is designed to run at by Citroen in the
first place is the most efficient - why else would every car manufacturer do
the same? A deliberate ruse for a shorter lifespan on their engines so you'll
be back for another car soon? Come on I don't think so.

There are many cars on this forum with 200-300k miles and going strong
and to a man, everyone will say it's because of regular quality oil changes.
I believe you're putting too much store in synthetic oil to correct a skewed
operating temperature of the engine - if you're doing that you may as well
run the engine normally and change the oil more often for semi/full synthetic
and be done with it. I think you're looking for trouble with a theory that
sounded good over a few pints?

Do I stand corrected on any points of my understanding here myself?
What are your thoughts on this - is it a brilliant idea or one doomed to failure?

Andrew

Posted: **Tue Aug 17, 2010 12:21 pm**

Hi Andrew

Removing the thermostat will make no difference whatsoever the the temperature it runs at if its being driven hard, thats mainly down to the size of the radiator, it will make the engine run cool when under light load which is a retrograde step as the purpose of the thermostat is to bring the temperature up to the optimum level for efficiency and wear as quickly as possible.

On the point of oil, I am one of those who get 2-300,000 miles out of their engines and I use the cheapest oil I can find with the correct spec, about £9.50 a can, but I change it every 5,000 miles.

My cars are all diesel which tend to last longer anyway but I am sure the same applies to a gas guzzler. Hope this helps.

Peter

Posted: **Tue Aug 17, 2010 2:33 pm**

Hi Andrew,

In a nutshell.
This guy is bonkers for all the valid reasons you have given above!
As Peter says frequent oil changes are the secret of engine longevity + avoidance of short journeys.

Ken

Posted: **Tue Aug 17, 2010 3:04 pm**

Car manufacturers spend fortunes developing their engines. Some nut who thinks he knows better is utter nonsense. Let him carry on. His Xantia won't last long, and he'll bugger off to some other car manufacturer, and bombard their enthusiast forums with crap.

Posted: **Tue Aug 17, 2010 4:54 pm**

Generally accepted engineering logic supports the responses given.
Citroen of course do not help with much published factual information about their engines.
In practice absolute running temperature value is not critical.
Otherwise Citroen would not have made a blanket 6 degree change to petrol cars thermostats a few years ago.
They made it retrospective.
As has been stated the engine should quickly reaching temperature then stay at a constant value.
Peter is right oil in satisfactory condition is the key to minimum component wear.

John

Posted: **Tue Aug 17, 2010 7:25 pm**

I think the Xantia bloke is getting himself a bit confused and reading the Amsoil Bullshit and actually believing it means what he thinks.

There are points to note about engine temperature.
If the EGT gasses are very hot it gradually degrades the piston crown and valves. Very hot is anything over about 750c on a regular basis.
As the oil heats up it thins in viscosity, which means it provides less wear protection, but oils are rated at 100c, so anything around there is fine, and if he's still bothered why not just uses a slightly heavier weight oil.

I think Andrew is correct with his reply points, a cooler engine is likely to suffer more wear due to mixture richening , increased condensation and lack of boiling off fuel from the oil.
He is also likely to suffer more blow-by as a result of the pistons not expanding fully into the bores.

Back to Amsoil;

* Amsoil Synthetics offer superior wear protection so that engines last longer
* Amsoil Synthetics improve fuel economy so that vehicles get better mileage out of every tank of petrol
* Because of Amsoil Synthetics low pour points and cold weather pumpability, they make winter starts much easier
* By reducing friction Amsoil Synthetics help engines run cooler
* By reducing deposits engines run cleaner and perform more efficiently
* Because of lower volatility Amsoil Synthetics reduce oil consumption.
* Amsoil Synthetics have been proven to provide more horsepower.
* Because Amsoil Synthetics resist oxidation and breakdown, they reduce varnish and sludge which keeps valves and rings from sticking.
* Amsoil Synthetics reduce waste. Not only is there less waste oil to deal with, there are also fewer empty containers for disposal.

I've emboldened the bits I think He is referencing as proof for his experiment. He is turning round their statement about synthetic oil reducing friction so keeping the engine cooler, into meaning that a cooler engine wears less.

If he really wants less wear just fit a bypass filter, run on synthetic oil and leave everything else alone.

Are we allowed to say Twat on here?

Posted: **Tue Aug 17, 2010 7:48 pm**

only under certain conditions Dman........such as these.
Madness, Andrew i didnt actualy bother reading his thread on fcf but you are 100% right, running cold will mean the petrol and acids wont come out of the oil in use shortening the lubricants life and running tolerances will be too big in the engine increasing wear massivly along with all the other problems you have mentioned if oil temperature stays low

Help those that help themselves, and he isnt helping himself at all so im not going to join in there.

D

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