Heater Core Firewall Junction/Coupler bypass - DIY write-up

Post by **JimBee** » 03 Feb 2015, 21:34

I used two 5/8" barbed hose elbows rather than reusing the copper fittings, but I doubt it's a big deal either way. The elbows are pretty, which was a major factor in my decision to use them.

I looked at barbed "L"s like those at HD and Menards and talked with plumbing clerk about heat ratings. He didn't have any data and the fittings weren't marked for heat. They were the black ones used in sprinkler systems, I think. Are the yellow ones heat rated? Does it matter?

Post by **j-dawg** » 04 Feb 2015, 11:22

Those black nylon coolant hose elbows, if that's what you're looking at, were standard equipment on early-'00s GM cars. Not really a high benchmark for quality, but somewhere an engineer decided that the plastic elbows would outlast the warranty period, which is probably fine for a 15-year-old Volvo.

Unless you're looking at steel fittings, in which case do not use them. They will rust, and you don't want that running around your engine block and water pump.

The brass elbows I used are rated for 160F on McMaster-Carr, which is well below the temperature of coolant. I did some high-performance Googling and found plenty of anecdotal evidence suggesting it'll be okay. Given that the thermostat is made of brass, I'm not too worried about it.

Post by **JimBee** » 04 Feb 2015, 21:16

Another option for the sharp 90 degree turn out of the firewall might be a molded heater hose that has the 90 L. I picked one up for a future fix from Advance Auto. It's plenty long enough to reach from the engine compartment down into the heater box to connect to the shortened aluminum tubing. That gets you the 90L on the firewall side, but you still need a link from the short end of the L to the block.

Or, on an n/a, you could use it the other way with the short end and L off the block and straight shot through the firewall.

The hose material is like the original Volvo heater hoses, probably softer so it will flex with no bending forces on the original firewall unions which is a non issue once those are removed.

I think it's a Toyota hose, 5/8" ID. The clerk took me back to the shelf and let me brainstorm and pick what I thought might work.

850TurboTurtle · Post by **850TurboTurtle** » 21 Aug 2015, 22:04

Simple hack: take the gutted coupler with you when you go to buy hoses. I have 5 different brand auto parts stores within 2 miles of my place, and I just went from one to the other to find a tight fit through the holes. The counter help didn't mind letting me poke the hoses through the hole to check.

Post by **abscate** » 23 Aug 2015, 05:30

I love the silicone hose gasket idea for the firewall junction. Nice implementation.

I just took off the 17 year old heater hoses on my 1999 and they were like new. If you have not oil soaked them, or live in an ozone capital, I think they out live the car.

On a turbo with tight quarters, I would stick with heater hose to OEM hose

bugs11 · Post by **bugs11** » 07 Oct 2015, 15:01

Where can I get 15mm inner diameter heater hose? I've been to two local auto parts stores and called a couple of dealers. No one has 15mm ID heater hose. The parts stores have 1/2" and 5/8", but 1/2" is to tight and 5/8" is too loose. I need the Goldilocks of heater hoses. Winter is coming, so I need to get his hack done. BTW - Car is running great after the head gasket replacement.

bugs11 · Post by **bugs11** » 07 Oct 2015, 16:53

Found some heater hose that will work at a parts store on my way home! The local Advance Auto has Thermoid 5/8" (15.9mm) heater hose - made in USA. No part number on the hose. While this hose is just barely snug on the heater hose fitting, it's a heck of a lot snugger than the hose I found at the other parts stores and will work.

Post by **mecheng** » 30 Dec 2015, 09:53

Which two brands of Heater Core did you try. There have been reported issues with the Ebay brand.

I recently installed a Spectra brand and there are no leaks at all. I applied a bit of silicon spray on the rubber o-rings, I do that for all my rubber seals as good measure.

Post by **cn90** » 30 Dec 2015, 10:08

My ebay (Estonia) heater core is now 8 months old, and zero issues.

Re couplers etc and all that jazz, there is a reason I don't want to go back to this Volvo convoluted setup.
I eliminated everything, and run heater hose to firewall ---> barb fitting ---> heater hoses to engine.
I use Gates brand: do this and you will never look back...

In the thread below: i discussed the use of an additional washer (copper) to engage the O-rings at the heater core better, so far so good with the extra washers.

DIY: 1998 Volvo S70 GLT Heater Core, Heater Hoses Rebuild!
https://www.matthewsvolvosite.com/forums ... hp?t=69238

Heater Core Firewall Junction/Coupler bypass - DIY write-up

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