Just wanted to share my solution.

Replaced the thermostat on my dad'* 2005 Buick Lacrosse CXS (3.6L LY7), but we couldn't find the heater pipe o-ring (GM part number 19351800, or its predecessors 12574367 and 12588986) anywhere in stock locally. Old one had taken a set and was leaking horribly when we tried reinstalling. Most places online list it as taking 5-10 days to arrive when ordered (dealer parts counter is no faster), and to top it off, it'* been discontinued, so when it'* gone, it'* gone.


GM heater pipe seal, part number 19351800. This diagram is likely from an Acadia or similar longitudinal engine vehicle, but demonstrates the same part and application as a 2005 Buick LaCrosse CXS with 3.6L LY7 engine.


Inner diameter of the thermostat housing is 0.750" on the nose, outer diameter of the heater pipe o-ring groove is 0.535". We chose to try an AS568-206 o-ring since it seems to be about the right size. -206 o-rings are nominally 1/2” ID, 3/4" OD, with cross section of 1/8", but in reality are closer to 0.484" ID x 0.762" OD, 0.139" cross section. We got some in Viton for chemical resistance, with a durometer of 75A. Ordered a pack of 1288N166 from McMaster-Carr, they fit beautifully. Installed on the heater outlet pipe, the o-ring OD is closer to 0.780". Lubed it with silicone grease, stuck it in, tightened it all down, et voila: no leaks, even when pressurized.

Old o-ring, which I'm guessing is 12588986 based on pictures online, showed some black underneath the peeled-off blue coating, so I'm guessing it was blue coated NBR. In this case, I can only see the Viton o-ring as an upgrade to this seal.

I'll update this post if that seal ever blows.

Just want to save somebody else some time and frustration in dealing with discontinued seals, especially as these cars get older and more components need replacing.

tl;dr If you're looking for 19351800, try a -206 size Viton o-ring with durometer (hardness) of 75A, such as 1288N166 from McMaster-Carr. Use silicone (not regular!) grease for assembly and move on with your life.

Thanks JwrKy!

Appreciate the write-up!

I'm sure this will help someone down the road. I even have an LY7 that might benefit!

Welcome aboard!

Just for the record, -206 size o-rings are sometimes better known as 1/2"x1/8" o-rings.

Given that this is a GM part from the mid-2000s, it may well be a metric o-ring as well, in which case a 3mmx13mm (0.512" ID x 0.748" OD) or 3.5mmx13mm (0.512" ID x 0.787" OD) o-ring might be closer to the original. Either way, however, the -206 is still holding pressure.

Cool!

Thanks for the follow up!