[T-Cut]

Originally Posted by marinabrian

Okay, so when were the version 2 and three introduced TC?, was this post production perhaps?

I've no idea when version 2 appeared, but it was of a different construction from the first one. I understand the original stats were branded BMW.



Again, my impression is they (v2) appeared on the Mk1's, so maybe it's a Project Drive difference?? Mike Noc might know since he was involved with the initial stage of the 'investigation'. He had a failed v1, which appeared to have a displaced primary valve. Or maybe it was its rubber coating that was displaced, can't remember exactly. Here's another of his images.



This shows a flow pattern on the rubber covering - note the 'shading' on the rubber. I believe it wouldn't close properly. I also understand that v1 was generally reliable.

I've only ever looked at thermostats removed from facelift diesels, and I've only changed a dozen or so in total. However in every case the failure was definitely not a result of a faulty waxstat

The v2 low temperature failures aren't visually obvious, they look perfect and are typically watertight in the valve. At the time, Jules said he'd changed 'hundreds' and every one was closed when removed. This indicates that the often assumed 'failed open' cause was a myth. The change is in the physical properties of the wax. It's melting characteristics alter and there was a fractionation observed. Part of the wax had a very high melting point (awell bove 100C) and it had a strange smell compared with unused wax. Overall effect of the changes was reduced opening point. In one example, the valve started opening at 55C. See the report for details on how this was done. As we now know, the smallest bleed-past in the valve has a dramatic effect on the running temperature. For that reason, some brands of the R4 in-line stat don't work properly.


EDIT: I also looked at the implications that water ingress to the wax capsule would have on performance. There are references to this in the literature and the possibility that coolant might 'react' with the wax was mooted.

Granted my testing only involved slowly heating in water until the pushrod was at full deflection, using a 0-275 degree type K thermocouple connected to my Fluke Hydra II, so the resolution of +/- 2 degrees may not be up to scientific testing standards.

I'm sure that's perfectly adequate, but the first point of opening is the critical one. A failed stat will no doubt be fully open at the specified temperature, but the engine will never get there.

So what was the difference in the wax composition that makes the V1 V2 and V3 different?

Again I have no idea what compositional differences exist in the three versions. I have only examined failed and unused v2 waxes. When v3 was introduced, the supplier apparently said they'd used a 'different' wax. How it was different I can't say. Typical waxes used in thermostats have always been fractionally distilled paraffins However, the failed wax I examined seemed to contain both a paraffin wax (a minor amount) and a material I was unable to characterise. I no longer had the ways and means to get the analysis done, and a promised Infrared spectrum failed to materialise. That might have been very informative. I'm familiar with very high melting waxes in the synthetic fatty acid amide family, which an IR spectrum would readily identify.

I'm curious as I have a leaking upper coolant rail to attend to on the old man's car, and if I'm replacing the o ring on the 'stat housing, I'd like to fit a thermostat that was unlikely to fail in the same way as all of the others I've seen.

The current 'v3' as listed by DMGRS seems reliable. At least over the six years since introduction there've been no concerns reported here. Whether the stats now supplied more generally use the same wax, I wouldn't know.

TC