Rover owners: O-rings - 1.8 thermostat housing

Hi all,

It is approx 9 months since I swapped the engine in my 1.8 tourer and things has worked greatly. I discovered a slight loss off coolant the last months and found the leak to be at the outer O-ring in the thermostat housing. Firstly I found it strange as I replaced both O-rings during the engine swap. One of them was a genuine seal from Rimmers, and the other one came from a low cost bottom end seal kit. Thermostat housing was removed and seals inspected. The inner O-ring was in sound condition. It felt soft and was only slightly deformed, which is quite normal. The other one was hard, cracked and deformed. It snapped during removal. No need to say that this one was not the correct grade for the job.

I did not have any OEM spare available so I measured the O-ring groove and picked a standard O-ring in a size and material grade based on common engineering practice which was a Ø33mm Inner Diameter with Ø3mm cross section. Material NBR/Nitrile. Everything put together and works fine. I have no doubt about the size, but would like to know what are the most common used elastomer seal material for OAT based cooling systems. For all I know, the cheap one was standard NBR material??

So what would the conclusion be??

Don`t by cheap, buy quality :)