I just replaced my O-ring seals for my heater core. The dealership didn't have any but they could order them. For what the dealership wants, I could buy them by the bag. The problem was finding what size to buy. I found conflicting information online so I took apart 4 heater boxes and measured the tubes, core side where the O-rings seat and the old seals themselves.

Here is what I came up with and what I bought. I thought this might help others if they are searching.


They are 16 mm ID x 2 mm round
I got Chemical Resistant Viton Fluoroelastomer O-ring, Super -Resilient, 2 mm Wide, 16 mm ID from McMaster -Carr. A pack of 10 was $5.02. Item # is 1295N241. Temp range is -15° - 400° and is compatible with many chemicals including Ethylene Glycol.

You can get whatever material you decide. This is what I bought. The OD is 20 mm.

 

I'm trying to include a link. https://www.mcmaster.com/1295N241

 

My local NAPA has a bin of various sizes of o-rings to choose from, and can be bought in singles. Rural King also sells singles too of various sizes. Don't know about Tractor Supply. Local hardware sells them too.

 

Nobody around my area had any that fit and I didn't know the actual size. So I got online and found conflicting information of the size. The dealership didn't even know. I saw many posts where people were substituting sizes in inches and guessing. Some people damaged the delicate brass collars forcing the wrong size on. I found posts where people gave up and soldered the tubes on or slapped RTV on. I'm just trying to save people the time and frustration. These fit perfect.

So my long winded post is to say get a 16 mm ID O-ring that is 2 mm thick. Preferably made of a material that can handle the coolant and temp range.