Quote:
Originally Posted by Randyjim
Simon,
I've removed some very flat 'OE' rings on a couple of occasions, so I don't believe these are fit for the job. At least not without finding a reliable supplier with genuine OEM product.
I recall that your EPDM experiment didn't end well either.
As I stated in my original post, I believe the leak is due to a slightly damaged bore, so this is the problem that I'm seeking a resolution for, and not the wider shortcomings of the design.
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The elastomer selection is a compromise, the manufacturer is caught between a rock and a hard place when it comes to selection and engineering.
In my industry we can only ever contemplate a double o-ring set up due to the consequences, but we are not selling low cost consumer items such as cars that are built to a price much like washing machines etc, where the costs are calculated down to the last washer hence only one o-ring used.
The type of elastomer selected for the thermostat assembly appears to be a EPDM material of relatively soft compound (shore perhaps 70 or so?). This will work well at low temp but also at high temps and will not take a set when compared to a harder o-ring such as duro 95 which suffers at colder temps but will have more resistance to failure at high temps and pressures.
The issue with the cooling system is the pressure is really low at 15psi and getting an o-ring to energise at low pressure and low temp can be challenging.
With EPDM you could argue that would be a better selection as when exposed to hydrocarbon the elastomer swells up significantly and would actually help close the extrusion gap between the materials. however a cooling system should not contain hydrocarbon unless the head had failed, but worth discussing anyway. Have you seen the EPDM coolant hoses on a car with failed head gasket where oil is in the cooling system, just observe the hoses and see how swollen they become.
I think MGR's engineering selection of relatively soft o-ring makes for relatively easy assembly into the bore of the component and will provide a long term seal, but as with age and as you have experienced the o-ring takes a set any scratches in the components can have a marked effect the o-rings performance. Unfortunately they fitted all o-rings dry which does not help. I have seen dry o-rings rolling upon fitting and leading to all kinds of leaks down the line.
Kaiser's thoughts on trying to source a slightly larger o-ring either in cross section or OD might be the most realistic option for you, and with the addition on Dow Corning DC111 silicone grease used upon assembly would give the best chance of a decent seal. The grease not only aids disassembly but long term exposure issues on elastomers due to hot coolant and allegedly exposure to OAT which I have never seen to date. A wee bit more cleaning up of the surface might be worth a punt too. With plastic components one cannot discount the fact the pin end itself maybe distorted leading to increased extrusion tolerances between pin and box. It would have helped if MGR or their suppliers had lined the plastic components with a metal sleeve to help avoid this, but again they are not different to any other manufacturer in the industry where a shaving a few pence off can make the difference when selling by the millions.
