Green ones are often HNBR and used in aircon. HNBR is listed as compatible with mineral oil and good temperature resistance.
The ring should fit into the groove without being either slack or stretched. If you put a straight edge on it, a rough guide is that you should have available compression of around 1/3 of the chord, eg. a 3mm chord should compress about 1mm.
Excellent that’s good to know.
Now that I’m fairly happy the o-rings are supposed to be there I’ve got a bit of confidence in my plan, especially after finding the dried out/cracking state of the o-rings that came out of it. Hopefully fresh o-rings, no PTFE/rtv gimmicks and I’ll just burn a load of fuel tomorrow with the car on stands to do whatever I can to pressure test it.
Your input has been invaluable, you should hang around here more often 
As for the sizes, it seems to be a shade under 1.5mm thick (I’m guessing 1.5 before it got crushed) and only my AC o-rings went that thin. The ones I’ve found seem to be perfect though, fingers crossed.
I just noticed which holes you’re on about. Ignore everything else I said !
OK me again, sorry. I found the original o-rings from when I first removed the coolers (I keep everything like that 
)
Judging by some very questionable vernier usage and comparing with a known size of 13.9x1.8 from my AC kit… I think the original o-rings were 13.5x1.5 based on the fact that’s the closest match I can find on: Metric O-Ring Size Chart | Metric O-Rings Sizes
So I’ll do what I can to source some 13.5x1.5mm o-rings in the next 24 hours, but how much ‘compression’ tolerance is really acceptable for something like this? I did a dry fit of the system this morning and everything has nipped up nice and tight/cleanly so I’m tempted to crank up the engine and pressure test it for a while. If anything I suppose going 0.3mm bigger on the o-ring is better than going 0.3mm smaller?! Really wish I could find the original spec so I could just order something with confidence.
Never seen the fittings with o rings before…
When i did the conversion on my Elige we used the alloy fitting with a conical seat like these
I thought from your last post that you meant the conical ‘seal’ was metal on metal, but that looks like a rubber seal in there which could sit in the groove that mine had o-rings sat into?
no seal metal conical seats
OK fair enough, probably just the lighting on the photo makes it look like a rubber insert of some sort.
I can only assume that Lotus used two types of fitting - both of which are ‘supported’ by the receiving oil coolers. Wouldn’t be the first time Lotus have swapped suppliers/spec of a part mid-run I guess but it’s certainly confused me a bit over the weekend.
I just noticed that the Lotus ‘hose recall kit’ (A120K0079S) is only £12 and would supply new ends completely - but I think my odds of getting that kit in the next day or so are slim to none. That would probably remove a fair few variables though!
I use Simply Bearings for almost all our o-rings. If they don’t have HNBR then NBR or Viton should be okay:
Measuring - measure the diameter at the root of the o-ring groove in the fitting, this will give you the i.d. for the o-ring, and measure the width of the groove which will give you the chord. From these two measurements use the drop-down lists to find the right ones on Simply Bearings.
O-rings come in two dimension groups commonly - either metric, in which case the measurements you get will be obviously so as these go in half millimetre increments. Alternatively there are BS sizes which aren’t logical metric (ie. not whole or half millimetre sizes).
It’s possible yours are the latter, since there is a standard BS chord of 1.78mm.
Don’t go about 40% chord on compression or the fitting won’t go together properly and likely damage the o-ring. The above measurements should give the correct size without any problem.
Once again I am in awe of the knowledge some people have about matters mechanical.
Great stuff, I’ll have a poke around later and double check my measurements.
For what it’s worth I’ve just been running the car in the garage for ~20mins or so (with the 1.8mm o-rings) , monitored the temps in the oil coolers and once they got up to temp I held persistent RPM for a bit to keep the ~5bar pressure up until my ears couldn’t take anymore… there’s not a drop to be seen, but I know that’s no substitute for a good road test… which is easier said than done with no clam on!
OK at it’s narrowest (the groove is tapered) it measures in at 14.4mm which is a good half a mm wide than the one I’m using (so suggests that I’m ‘stretching’ mine by about 3.5%) The “OEM” one that came off is even smaller still, probably closer to a full 1mm smaller than the groove.
Again because of the taper in the groove I can’t really rely on the chord measurement either. I’m now leaning towards sticking with the 1.8mm rings that I have in place right now and just spending the next 24 hours running it at pressure for as much as I can.
In the meantime I’m going to get the Lotus ‘kit’ for the hose fittings backordered and I can always look to replace the whole lot next time my clam comes off, unless I spring a leak sooner than that… 
BS015 is 1.78mm chord, 14mm i.d., which gives an o.d. of 17.56mm.
Having been on the back of a stone strike to an oil cooler on the way to Anglesey a few years ago, I know exactly what it is like, the oil is everywhere, it is all in a fine mist all over the wheel brakes suspension etc.
My car sat in the car park all that day sulking and dripping oil, I drove the car home very gingerly and gently and because I did that the oil coolers were barely functioning so it lost next to no oil, quite different to the trip round the Evo triangle where I sustained the damage and I used half a litre. Trust me when I say if it is leaking, you will know for sure!
I also concur with everyone else, leave the coolers on, there is little to gain by removing them, if you go charge cooled even with a triple pass rad the cooling is going to work hard, as soon as I added a laminova gearbox cooler, I was on the limit of the what was the overall cooling package could do, it would have probably been ok without AC on the car, but I like AC!
If you become desperate Kyle, I have a kit as a just in case (minus one o’ring). Just give me a shout. 
Cheers guys, this thread has been really quite helpful!
I toddled off to a local hydraulics place today and came back with an array of o-rings in the region of this size. After all that, based on my eyeballin’ and what ‘feels’ right I think the original size that I had (now believed to be 13.9x1.78 is the closest match and makes for the most ‘comfortable’ fit.
I’ve probably burned through half a tank of fuel idling/revving on the drive and even went for a clamless lap of the village, much to the delight of the young uns’. I’ve not yielded a drop of oil so I’ll do a bit more testing tomorrow before I bite the bullet and refit the clam. I don’t think I’ll ever be confident in it until I put some road miles on.
To give this thread a bit of colour, I did have to tart the coolers up a bit first before they went back on.
Whilst rolling around checking for leaks, a great big blob of rust caught my eye from the tow post that I fitted brand new over Christmas. It was the internal thread, and found the tow post wouldn’t even screw in without attacking the thread with an M8 tap first… not great after a few months. I knew Chris [mention]Type116[/mention] had been knocking up some beefy options recently so got on the blower and within a few hours he had me one ready.
It’s hanging up now with a coat of primer, it’ll be satin black by tomorrow lunch time. Usually would powdercoat, but time is of the essence!
Heck of a difference there!
wow, what a big ring you have 
All the better to pull you with!
