1998-2000 V70 Evaporator - Heater Core and O-rings issue

[lexmia]

I understand that Volvo makes cars since 1927 or so but... what were they thinking?

I finally decided to tackle the evaporator replacement in my 1998 V70 base model. I had also by-passed the heater core a few months ago, so i decided to replace it along with the evaporator.

A lot has been said about the replacement procedure itself. What about the causes of the problems?

My findings,

Evaporator Failure:
The evaporator in my car failed because the geniuses in Sweden, decided to secure, the longer evaporator tube (high pressure side) to the evaporator itself, by using a plastic clip inserted in between the evaporator fins. The clip is made of hard plastic and the serrated prongs in between the fins, have a rectangular cross-section, with very sharp corners. The result, the sharp corners will stress the thin aluminum evaporator to the point of puncturing it. See the attached picture.

The OEM Hella/Behr replacement comes with the same clip... geeez...

Heater Core failure:
The climate unit, with the evap, heater core, vent doors, etc. is secured to the body with 4 bolts through the 4 tabs on the upper part of the unit. This unit, thus hangs from the body. There are no bottom fasteners. Under normal driving stresses, the plastic unit will flex but.... wait... the metal heater core pipes are firmly attached to the coupler on the firewall and the heater core itself. Thus, the bottom plastic tank of the heater core is an unintended support for the climate unit... again, geeez... See the attached picture.

This explains why the heater core in my car cracked open when I was making a rather fast, sharp right turn!! Not funny when your windshield fogs, antifreeze ruins your radio and your engine cooling system gets seriously compromised without any prior indication of failure.

About the O-rings:

The firewall coupler for the heater core hoses, the metal pipes between the coupler and the heater core use a total of 10 o-rings. From the 2 Volvo rings gotten from FCP at $4.00 and change each, the rings are a standard dash 114 size. The trick is the material the rings are made of.

I did some research, and base my conclusions on actual study test results available on-line, not o-ring manufacturer sale pitches.

Keep in mind that:
- There is lots of misinformation about the suitability of o-ring materials for different applications. There are tables that show Neoprene being unsuitable for coolant use and some others put it as the preferred material.
- The same materials, e.g. Viton, come in many different formulations with very different properties.
- The same materials, e.g. HNBR, come in different colors, green, yellow, blue and black. Viton comes in black and brown. Some manufacturers offer to mold the o-rings in the color of your choice, so color is not a good reference.
- O-rings and other rubber parts age, even on the shelf, and they do not age for better.

Buna (nitrile), is good for water, but does not have good resistance to alcohols (as found in engine coolants). Some formulas are recommended for use between -20 to 212F, the 212F too close for comfort, in case of an engine overheat. Most Buna seals in hydraulic use are not to be heated over 160F because they will shrink and cause leaks.

FKM (Viton) is fair for use with water but not resistant to alcohols or antifreeze. Only newer formulations are suitable. Use between 0 and 390 F. One study showed material breakdown in antifreeze after 1000 hours. One Mazda enthusiast reported excellent results in using Viton o-rings for the rotary engine coolant seals.

HBNR, hydrogenated BUNA, has better chemical resistance and temperature range, but studies show that they perform lousily under hot water/coolant. According to the study by Evans Cooling, they are not suitable for engine coolant applications.

Silicone is only fair in water, and does not seem to hold well with alcohols, antifreeze, or hot water.

Neoprene, the oldest man made elastomer, has a temperature range from -40 to 275F (Mc Master O-ring listing) Is recommended for Alcohol, engine coolants, hot water, etc. It has limitations with synthetic lubricants, gasoline, some solvents, and others. It has excellent mechanical properties.

I ordered 100 neoprene rings from Mc. Master for $4.09 plus shipping.

As important as the O-rings themselves, are the backup rings that go inside the coupler and on the heater core metal pipes. I decided to use split teflon backup rings as used in mid pressure hydraulics. 50 pieces for $11 and change.

When disassembling, I found the other problem bugging these cars... the quality of some the plastic parts is terrible... a couple of examples:

The housing of the steering column, airbag coiled wire assembly, is made our of polycarbonate (PC)(plexiglass) which is excellent for impact, but fair at best for chemical resistance and tension loads. The grease used in the horn slip ring, just destroys the PC. The prongs supporting the assembly were broken, chemically and stress cracked, leaving the assembly free to move around the steering shaft, being held only by the wire harness connector. You must have seen how nicely PC headlamp lenses age. A trip to the junkyard revealed that all these assemblies suffered from the same problem. I was able to find one that was weak but not broken off, and I was able to reinforce it with epoxy.

The lower cover for the ignition, windshield and turning signal switches is made of PC/ABS mix. Most of the parts I have encountered, made out of this mix, will age miserably. The bosses for the 3 screws that secure this cover were broken off.

The center console, arm rest cup holder. Broken.

The shifter position indicator bulb housing, broken.

The center console, arm rest hinge bosses, cracked.

Anyway... i feel better now after venting here.

I hope this information helps someone in the future.