Club 80-90 Forums

Suddenly noticed a slow drip under the van today.

After wriggling about underneath I have a drip falling from one of the O/S push rod tubes and one on the O/S rubber gasket on the head. Both are coolant leaks . I presume the one falling from the push rod tube is most likely fron the gasket but is tracking its way there.

Is this a head off job and why has it suddenly started dripping now the weathers gone cold?. It's been ok and hardly used since October and this leak has seemingly appeared from no where, i.e. not from along run etc etc.

If I run the van the leaks stop.

Tony Tone wrote: Is this a head off job and why has it suddenly started dripping now the weathers gone cold?. It's been ok and hardly used since October and this leak has seemingly appeared from no where, i.e. not from along run etc etc.

If I run the van the leaks stop.

Yep, head off. Head heats up and expands, seal tightens and reseals ... for now.

Does the cold adversley affect the rubber seal then ?.

Rubber solidifies/loses elasticity the colder it gets - the older the rubber the less flexible it is anyway. So while the seals may perform with the engine warm and expanded, once it goes cold and contracts the rubber is less able to expand to 'take up the slack' so to speak. That's my understanding of it at any rate.....

The funny thing is that rubber actually contracts as it warms, because of how the elastomer chains use heat.

There's a good experiment that I remember from college where you have a wheel on an axle, suspended by rubber bands, with the bands being heated by a lightbulb. We all expect the wheel rim to fall on the heated side (rubber expanding with heat, rim moves outward relative to axle, wheel rim descends on that side) but in fact it does the opposite!
The rubber bands contract and the wheel rim rises on the side nearest the heat source.

It's a demonstration of our preconceptions of material properties.

So the water jacket seals might well be harder when cold, but are bigger/thicker. Elasticity is definitely increased with heat though.

Could well be that a marginal water jacket rubber will dry out as the engine gets hot, so you only see the leak when it's cooled down.

silverbullet wrote:The funny thing is that rubber actually contracts as it warms, because of how the elastomer chains use heat.

.

thats a crock of crap .. Rubber has a coefficient of linear expansion of 77 x 10-6 m/mK. In comparison to other substances, this value is quite large.
What you are descibing is entropy.

silverbullet wrote:There's a good experiment that I remember from college where you have a wheel on an axle, suspended by rubber bands

you do mean rubber bands rather than elastic bands? Only ask as I was unaware of rubber having that characteristic....

Rubber seals - like tyres, hard when cold, softer when hot. They also tend to harden with age.

O ring type seals (not familiar with the type of seals being discussed) work better with some pressure to force the seal against a face or bore/shaft.

Mick.

kevtherev wrote:

silverbullet wrote:The funny thing is that rubber actually contracts as it warms, because of how the elastomer chains use heat.

.

thats a crock of crap .. Rubber has a coefficient of linear expansion of 77 x 10-6 m/mK. In comparison to other substances, this value is quite large.
What you are descibing is entropy.

You could well be correct Kev.

Here's a snippet from the usual source:

Thermodynamics

Main article: Rubber elasticity
Temperature affects the elasticity of a rubber band in an unusual way. Heating causes the rubber band to contract, and cooling causes expansion.[9] One can observe this because stretching a rubber band will cause it to release heat (press it against your lips), while releasing it after it has been stretched will lead it to absorb heat, causing its surroundings to become cooler. This effect is due to the higher entropy of the unstressed state, which is more entangled, and therefore has more states available. The result is that a rubber band behaves somewhat like an ideal monatomic gas, inasmuch as (to good approximation) elastic polymers do not store any potential energy in stretched chemical bonds or elastic work done in stretching molecules, when work is done upon them. Instead, all work done on the rubber is "released" (not stored) and appears immediately in the polymer as thermal energy.

All academic really as o rings are usually made of silicone, fluorosilicone, ethylene-propylene, neoprene, polyurethane, Ethylene Propylene, butyl... etc
It depends on their application

Brake seals are the only one that springs to mind that are natural rubber

My shiny black rubber suit and mask do seem to get noticably 'tighter' after a few minutes of me wearing them so maybe there is some truth in it.......

1664 wrote:My shiny black rubber suit and mask do seem to get noticably 'tighter' after a few minutes of me wearing them so maybe there is some truth in it.......

Bren, remember ...

I was suffering from low self-esteem back then Ian. I have since dropped a few pounds with a corresponding reduction in gaseous emmissions

And there was me worried about admitting my 'E' grade in A-level physics

So, about this dripping problem...

Sooooo, will chucking K Seal or some such in give me some added miles. Its a tiny drip at the moment and loses about 1/2 pint a month !. As I said, when the engine warms up, the drip stops. In fact, now the weather is warmer, the drip has gone away !. Puzzled of Birmingham