The Function and Malfunction of the Diesel Thermostat

[FrenchMike]

My last experiments:

I have put the wax into a small medical glass syringe.(needle closed by a bulb of solder)
melted it and vacumed air.





But no difference between boiling water and ambiant temp ; no movement !!
What is the expansion rate expected ?

TC Any idea ?

[T-Cut]

Originally Posted by FrenchMike

What is the expansion rate expected? TC Any idea?

From what I've read about thermostat waxes, they expand about 12-15% at the melting point.

TC

[FrenchMike]

Originally Posted by T-Cut

From what I've read about thermostat waxes, they expand about 12-15% at the melting point.

TC

Well,so hard to see ,i'll try again and look more closely ..

Effectively,the volume of the displaced piston is about 0.1 cm3 only.

[Jules]

The other factor is that the Wax will be under slight pressure within the caosule acting against the spring.
All the present experiments are being carried out at Atmosphere.

TC I can send you an early failed stat.
(from a 2001 which had a rubber seating which they deleted on later stats)

[COLVERT]

Originally Posted by Jules

The other factor is that the Wax will be under slight pressure within the caosule acting against the spring.
All the present experiments are being carried out at Atmosphere.

TC I can send you an early failed stat.
(from a 2001 which had a rubber seating which they deleted on later stats)

I suspect the wax would be virtually incompressible cold even with a force much greater than the spring can generate.

[T-Cut]

Originally Posted by Jules

The other factor is that the Wax will be under slight pressure within the capsule acting against the spring.
All the present experiments are being carried out at Atmosphere.

I suspect Mike's experiment is ambiguous because the wax may not be fully melting. The thermal conductivity of the glass syringe will be quite low compared with the brass capsule. From my own tests I found it very slow melting at 100C stood on aluminium foil. There may be only superficial liquefaction where it's in contact with the glass.

TC I can send you an early failed stat.
(from a 2001 which had a rubber seating which they deleted on later stats)

Yes please do. From what I saw in mikenoc's photos, I think the wax is different in these but it needs confirming.

A chemical change in the later 'aluminised' wax appears to cause the low opening behaviour, apparently by the generation of a volatile byproduct. It clearly suggests that this type of stat has a limited service life. I doubt there's any way to understand it without proper lab investigations. Even then, it might take a long time to simulate the breakdown

TC

[FrenchMike]

I have redone the experiment and i hardly found a difference of 0.5 millimeter...
(5 minutes in boiling water)...

the one on my car is genuine and still works well at 88 deg (11 years old,120.000km)
never overheated ..

[crofts]

Thought my car was sluggish getting up to temp/hot air in cabin.
Should have checked the OBD method first but thought the pushing of the trip button was beyond me. Anyway, saw a much simpler explanation from another member and got it right first time. Found the temp gets up to 83-84 in about 5 miles which is probably fairly normal.
So doubt the inline stat I bought (£55) will improve this much, if at all, though I would like to get it up a bit from 83-84

[T-Cut]

Originally Posted by crofts

So doubt the inline stat I bought (£55) will improve this much, if at all, though I would like to get it up a bit from 83-84

I'd suck it and see using the push-in type, you might be surprised. The cut hose/housing type may not be worth the trouble without first testing the principle. I'd try the Renault 89C one myself.

TC

[Gate Keeper]

Can anyone please tell me if the wax is standard across all thermostats in all car models? There is a reason I ask.