eric_in_sd

So I started having the sticky thermostat problem. Won't close all the way.

FCP Euro warned that the o-ring is often not reusable. Since the rest of the rubber, e.g. hoses, is in great shape, and I was in kind of a hurry, I thought I'd chance it. Plus it irritates me no end that someone charges $10 for an o-ring. I considered replacing the hose but by the time I got around to seriously considering that, it would have taken too long to get the hose.

So I chanced it ... and failed.

The o-ring I took out was significantly loose, like it had grown. I eased it off and cleaned it, lubing well with silicone grease, and reinstalled ... and there it goes, leaky leaky. Pulled it out to see the o-ring had either broken or been severed. Tried to find a replacement o-ring, but O-Rings-R-Us was closed. So the truck is sitting in my buddy's driveway on the other side of town and I am waiting for the replacement hose to show up.

I assumed if the o-ring was bad it would go bad in some typical way, like crumbling or rotting. I didn't bank on it swelling and that being the reason it is not reusable. I'm also kind of retarded for not thinking through what I would do if the o-ring was not reusable.

When I get the new hose, I'll measure the o-ring; if it's an ordinary black nitrile rubber (does anyone know if it has special characteristics?) one should be able to purchase a set including one for less than a single MB item.

Kinda irritated with myself, tbh - I'm a little tired of "living and learning".

DennisG01

Yeah, been there done that... and then you're kicking yourself because you tried to save a few bucks only to have the vehicle down for a few days and end up spending the money in the end, anyways.

I don't have the answer for "why" they swell, but it seems in some applications they do that. I always thought it had something to do with ethanol - and I imagine there would be traces of it in the oil? Sometimes... a little trick is to put them in the freezer right before installation. Although I've done that, I suppose that could lead us right back to where we started and kicking ourselves...

eric_in_sd

Well, in this application they are only exposed to coolant.

Perhaps the absorption is desired in this application: You want the o-ring to swell and seal. I didn't read of it as a feature at an o-ring vendor, though.

O-rings are a nightmare. Since there are two dimensions, diameter and thickness, you can drive yourself crazy trying to match an o-ring without knowing the exact size. Stiffness is yet another dimension, but fortunately there is not as much variation nor is it that critical.

DennisG01

Oh, right - coolant! I don't know why I had engine oil in my head when I responded!

I doubt it's an intended "feature" of the o-ring to swell

I have a fuel cooler on my Yamaha outboard - it's always bigger when I take the cooler apart to clean it.

Yeah, you can definitely drive yourself crazy "internet searching"... sometimes I think ahead and just think "It's going to take me X amount of hours trying to figure this out... my time is worth more than that and I should just pay the extra money for the "special" MB o-ring".

chassis

Good practice on vehicles is to replace rubber items “while you’re in there”. Always replace seals, o-rings, gaskets, crush washers, etc.

eric_in_sd

Yeah.

It varies, though. I haven't changed the oil filter o-rings in forever. I give them a visual inspection but that's it.

FYI crush washers can be reused. The reason you are not supposed to is copper gets work-hardened. Thus when you crush it once, it becomes un-crushable. The cure for this is to anneal the washer by heating with a torch to red-hot and allowing to cool slowly. You then have to polish off the oxidation. More trouble than it's worth, of course, unless you get a kick out of that sort of thing or don't have a replacement handy.

I probably could have salvaged the coolant o-ring by boiling in distilled water (which would dissolve out the coolant that had penetrated the o-ring) and then letting the o-ring dry. Butyl rubber is permeable to water, so it makes sense the o-ring swelled. I saved the broken o-ring and may try this.

eric_in_sd

Tried it. No help. The o-ring appears permanently distorted. So if the o-ring has been in place for a while, forget about reusing it.

I forgot to measure the o-ring before installing the new hose, but I measured the channel it fits snugly in. The channel is 40mm ID, 4mm wide, so the o-ring should be an "R-28", 38mm ID and 3.5mm thickness:

But there is a gajillion different size o-rings out there; I'd just be hoping that the one used on an ordinary automotive part would probably be in a comprehensive kit.

EWT

I've got a couple of boxes of o-rings of various sizes from Harbor Freight that weren't terribly expensive.. They have come in handy more than once. Probably not the highest quality available, but no failures to date.

eric_in_sd

Probably nitrile rubber is fairly standard. But with Harbor Freight you never know. Made from recycled Chinese condoms, perhaps?

All the o-ring kits I see are nitrile. I was assuming it was butyl. Nitrile is superior, anyway.