Multiple defective aftermarket heater cores

[S Carlson]

I bought a cheap MTC heater core from IPD. Installed it easily thanks to Robert's lovely video! But it leaked. I thought I must have pinched an o-ring, so I put new o-rings in. It still leaked, so I took it out. Turns out the o-ring bosses were not round, so it had no chance of sealing!

See photos below:
If the pictures don't work, just let me know and I will post links to the google album.


Should have listened to Robert. I returned the bad one and bought the nicer one from Swedish Car Parts on ebay, which has a lifetime warranty, and has been recommended by many people. Didn't even try to put it in, because it is ALSO not round! And in the exact same way as the other one! These things look like they are all made from the same mold and they are all bad.




Do we think a Behr one will have the same problem?

I sent a message to Swedish Car Parts about their heater core. Hopefully they will let me return or exchange it! I will post once I hear from them.

I am a decent machinist. I may buy another cheapo one and modify it to take thread-in barbed fittings and nix the entire hard-pipe system through the firewall.

What a mess! Anybody else encountered this? I have to say, the one thing I've learned in all this time is that Volvo sure did make it easy to change the heater core. I will forever be grateful for that.

I hope y'all can see the images I posted. If you can't, just holler and I will try to fix them.

[scot850]

Do these not use 'O' rings on the pipe ends? If so it should not necessarily matter if the recess is not totally round. What is important is the 'O' ring gets compressed evenly as it is the faces that do the sealing. Having said that, what does the 'O' ring look like when in the hole? Does it touch the sides in the 'round' part? In other words, if you fit the 'O' ring over the pipe stubs what is the overall diameter of the 'O' ring relative to the 20mm diameter of the recess on the heater core hole?

I know several people have had issues using the supplied 'O' rings. Only use the OE rings as they tend to be a little thicker and compress and seal better. I used a Behr and used the supplied rings and it leaked. Removed the rings and used Volvo. All good!

Neil.

[S Carlson]

Yes, they do use o-rings, as I mentioned I was worried I'd pinched them in my original post. The o-rings are normally installed on the pipes, and they seat in the plastic o-ring boss on the heater core, which is out-of-round, which is why they aren't sealing.

I've measured the o-rings, both dealer-supplied, from IPD/MTC, and from Swedish Car Parts. They are all pretty much identical - some may be softer or harder, and this may be causing the issues you describe.

O-ring bosses should be round, if they are designed to seal to the round pipe. Manufacturing tolerances exist, but this is a whole mm out of round! My intuition based on my experience plumbing all sorts of janky things on cars, in lab equipment, and in houses, is to assume that it won't seal. And I was right. Twice.

But we can do some math to prove it's a fool's errand to continue with these cores. The o-ring is only 2.62mm thick. The pipe is rigidly 15.875mm in diameter. Heck, we can be optimistic and say it's 16mm for the sake of argument! So 16+2.62+2.62 = 21.24. Subtract 21mm (the o-ring boss ID in its longest aspect) from 21.24 (optimistic o-ring OD when on the round pipe), and you get 0.24mm of total o-ring deformation on the long aspect of the o-ring boss. Divide by two, assuming it's deforming equally on both sides, and you get 0.12mm deformation on each side. That's only 4.5% deformation. For a static seal in a Buna-N o-ring, according to the Machinery's Handbook, you need at least 10% deformation. It's not gonna work!

Perhaps if I gently ovalized the pipe using vise-grips, it would work. I'm not going to do that. Suppliers should supply decent parts!

I also think it's a good case-study to see that the o-ring bosses are deformed in exactly the same way across multiple brands (some with a lifetime guarantee, some bargain-basement brands). I think it says something about modern manufacturing. Looking at the pictures, these clearly came from the same mold, and that's interesting considering their reputations.

[FireFox31]

Here are the connections on a Behr / Hella heater core. I bought this from eEuroparts in May 2018 for $120 (it's been on my shelf ever since). FCP now sells Mahle Behr cores for $90 so perhaps they're the same.

I measured the inner base of the hole openings with calipers. They slant inward so will appear different from your measurements. They range from 19.5mm to 20mm in diameter. There may be measurement error by not placing the calipers exactly opposite (reading less) or not exactly at the base (reading more). Most readings were 19.8mm to 20mm.

I prefer and recommend buying the best reasonable quality parts for critical components like the heater core. I'd only buy Volvo brand or whoever actually makes them (Mahle Behr, maybe Nissens?). I hope they still make them to the quality of the 2018 one that I have.

[S Carlson]

I agree.

But now that I've had it all apart, I kinda think the whole system is a bit of a lousy design, with the pipes and many o-rings and plastic quick-connects and all. I know that it has lasted 24 years (probably 22 years before it started leaking), but still, I am nervous about those potential failure points, and I know I have seen other cooling systems (with just hoses) last longer and be cheaper to repair! I really want to just tap and screw in some hose barbs in place of the o-ring bosses and run hoses through the firewall. I am slightly worried that the barbs would then be in the way of removing/installing it, but I could try it and see.

In the meantime, Swedish Car Parts is sending me a new core for free. We will see how that one looks!

[Sveedy]

There are easily more O-rings in this car, than all of the other cars and trucks I have owned in my life combined.
One of those weird design things that really doesn't seem to make much sense. In most cases I think a gasket would work better overall.

[S Carlson]

FireFox31, thank you for the picture! Your OE one looks pretty nice!

OE also looks nice because (in the pics I've seen anyway) the fins are more closely spaced than the aftermarket ones. Not sure how much this matters in the real world, however. We hear reports of good heat from many users of aftermarket cores.

For now, my slightly leaky OE one is back in the car. I think it's just seeping. In fact, I think the main leak from it was actually from the factory o-rings failing. Although, the core itself definitely has some crusty spots.

Sveedy, yeah, I agree! I think it was done this way to reduce labor needed to assemble the cars in the factory. But it definitely increases complexity, often needlessly so. A fair compromise would be Oetiker clamps on rubber hoses. Speedy assembly and non-finicky replacement.

[abscate]

The place where you lose simplicity using two hoses is the bulkhead , which has to be sealed tight to prevent exhaust from being drawn into the cabin. That’s hard to inspect, and 50 ppm of CO is a bad day.

[454cid]

The place where you lose simplicity using two hoses is the bulkhead , which has to be sealed tight to prevent exhaust from being drawn into the cabin. That’s hard to inspect, and 50 ppm of CO is a bad day.

I would think a piece of closed cell foam with two holes slightly smaller than the heater hose should work, if there's something on the inside of the firewall to keep it in place.

Reading this thread make me want to flush my heater core, and change my coolant..... which I suppose I should be doing any way, given I have no history on it.

[abscate]

It’s doable, but the danger is real if you don’t get it right. It’s very hard to inspect that part. I had an amplifier cable on the Kat running through the firewall without seal, and I got exhaust smell in that car even with a perfect exhaust. There is a lot of draw into the passenger compartment.

More sleuthing…look at the defects on those two molds, identical. It does like both SCP and MTC buy the same molded part from someone , or one of them makes it and sells to the other.

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The Behr one, also has dome small cutouts on the side. Function unknown. Possible mold release?

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