Car D.I.Y.

[johnnyb47]

Ohhh ok , There's a new angle on what it could be.
90c on my car dash display is right in the middle and from reading the Haynes manual the low speed fan should come on at around 98c (which it does)
To me that also seems a little high as you say.
Cheers @raleighnut

 

[raleighnut]

Ohhh ok , There's a new angle on what it could be.
90c on my car dash display is right in the middle and from reading the Haynes manual the low speed fan should come on at around 98c (which it does)
To me that also seems a little high as you say.
Cheers @raleighnut

The Fan will be on a different 'sender' unit to the temp gauge, I'd change the thermostat first. If the Haynes manual says fan cut in temp is 98c then I'd believe them, Haynes are pretty accurate. Just seems a little high for me but I'm 'old school', more modern engines do run a bit hotter to improve fuel economy with ECU's and fuel injection compared to old 'points and carb' engines.

 

[CXRAndy]

Hi,
I have a quick question and from my common sense I think I may know where the problem lies.
But before I get the spanners out,I thought it wise to ask here to whether you agree with me or not.
My car is a little Peugeot 206 cc 2 litre petrol ,and when I start it from stone cold the temperature gauge will rise to 100c ( 3/⁴ on the gauge)
After a half a mile or so at this temp, it will sharply drop to 90c and then settles around 91 to 94c no matter what the driving conditions are like.
I've never had a car where the temp needle has behaved in this way.
On all the car's I've had, the temp needle would just simply go to the middle 90c ish and stay there.
It doesn't use any coolant and there's no signs of head gasket failure ie steam from the exhaust, mayo coloured oil or over pressurization in the system.The two speed rad fans also work as they should.
I'm hedging my bets on a sticky/lazy thermostat not reacting quickly enough to the ever changing engine temperatures.
What's your guesses
All the very best,
Johnny 🤔

I would go for thermostat first. It could be head gasket leaking. See if the radiator or expansion tank has pressure build up, by carefully unscrewing the cap(protect against burns). Checking for bubbles in the expansion tank when the car first starts.

 

[johnnyb47]

Hi @CXRAndy
It's definitely not the Hg
There's no over pressurization in the system.
I'm quite up to speed knowing the symptoms having owned cars with the fabled k series engines of rover 🤣

 

[Pinno718]

... modern engines do run a bit hotter to improve fuel economy...

There exists a collective engineering amnesia.
There was a term banded about in the late 80's and this term was 'lean burn'. What this referred to was the push towards* the stoichiometric point in terms of fuel to air ratio. This, the absolute optimum point of efficiency and fuel economy. The circle needed to be squared: Better fuel economy, less emissions and more performance. The downside is that modern 'lean burn' engine combustion temperatures are very high. The upsides being catalytic converters are happier at higher temperatures and the hotter the combustion temperatures, the more hydrocarbons are burnt.
The other downside is that you need efficient cooling systems which run at higher pressures with higher concentrations of coolant as it's harder to maintain optimum running temperatures when that optimum temperature band is pretty narrow.

*Very hard to achieve but the optimum point would theoretically be 14.7:1

As to the OP: take the thermostat out. It should have the opening temperature stamped on it. You can put it in a pot on the cooker in cold water and measure the temperature at the point it opens if you have a temperature measuring device and if you have water and a pot and if you have a cooking device or the means to make fire ug.

 

[johnnyb47]

Thanks for great advice.
I forgot to mention i had the thermostat changed almost a year to the day last year when I had the cam belt changed.
It had failed by sticking open.
I could see it had happened just by when I was driving it.
The coolant temperature on the dash dropped off to around 80 instead of its unusual 90c.

 

[Drago]

There exists a collective engineering amnesia.
There was a term banded about in the late 80's and this term was 'lean burn'. What this referred to was the push towards* the stoichiometric point in terms of fuel to air ratio. This, the absolute optimum point of efficiency and fuel economy. The circle needed to be squared: Better fuel economy, less emissions and more performance.

Improved CO2 and HC emissions, but theyre a nightmare for NOx. Thats what killed them even before anyone was getting excited about NOx.

 

[raleighnut]

There exists a collective engineering amnesia.
There was a term banded about in the late 80's and this term was 'lean burn'. What this referred to was the push towards* the stoichiometric point in terms of fuel to air ratio. This, the absolute optimum point of efficiency and fuel economy. The circle needed to be squared: Better fuel economy, less emissions and more performance. The downside is that modern 'lean burn' engine combustion temperatures are very high. The upsides being catalytic converters are happier at higher temperatures and the hotter the combustion temperatures, the more hydrocarbons are burnt.
The other downside is that you need efficient cooling systems which run at higher pressures with higher concentrations of coolant as it's harder to maintain optimum running temperatures when that optimum temperature band is pretty narrow.

*Very hard to achieve but the optimum point would theoretically be 14.7:1

As to the OP: take the thermostat out. It should have the opening temperature stamped on it. You can put it in a pot on the cooker in cold water and measure the temperature at the point it opens if you have a temperature measuring device and if you have water and a pot and if you have a cooking device or the means to make fire ug.

Yep earlier engines were partially cooled by the fuel with I suppose the worst offender (other than 2 strokes) being the VW 'flat fours' abysmal fuel economy (reliable though)

 

[Pinno718]

Improved CO2 and HC emissions, but theyre a nightmare for NOx. Thats what killed them even before anyone was getting excited about NOx.

They got uppity about a lot of things back then - Tony Benn, Fergie, Eddie Shah, Maxwell, Monday's...

 

[Pinno718]

Yep earlier engines were partially cooled by the fuel with I suppose the worst offender (other than 2 strokes) being the VW 'flat fours' abysmal fuel economy (reliable though)

Sure but people forget how much cooling oil does. Oil performs the primary cooling function of the pistons for example.

 

[raleighnut]

Sure but people forget how much cooling oil does. Oil performs the primary cooling function of the pistons for example.

Yep Suzuki exploited that with their GSXR 750, massive oil flow to the cylinder head and jets pointed at the bottom of the piston crowns, meant the weight was much lower than the watercooled bikes it was up against. Memory is fading over the years but I seem to remember it having either 2 oil pumps or a 2 stage pump with a high pressure circuit for the crank etc and a high volume flow for the oil cooler and cylinder head cooling.