Metal vs. plastic relays

Hi there, any thoughts on using old-but-working metal relays vs. replacing with new-but-plastic relays? My metal relays work for now, and probably dissipate heat better (if that matters) but are celebrating their 40th birthday this year and it seems prudent to update them. Then again, a lot of things were made better in the 80s compared to quality you get today.

Also can anyone confirm the QV owners manual has a typo - relay E (external lights) is noted as Bosch number 0332015066, but more likely that part number should be 0332015006, correct?

Thanks,
Mike
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The relays have point contacts inside that will wear with use, not time. The very thin copper wire coils might degrade with time (or a voltage spike). Some of the relays will have had fewer on off cycles than others, so they will wear out at differential rates. Switch some of the same ones around from the higher use to lower use circuits, this would be one approach to getting the maximum lifespan out of all of them. Get a couple of plastic ones as spares and carry them in your trunk.

I have only had one relay fail in my Mondial 3.2, for the ac compressor. Makes sense as this one cycles on and off quite a bit, and of course it was one of the Italmec relays no longer available (there are work arounds to use a modern relay replacement).

 

I have a box of old Bosch relays with metal cans I have saved over the years. They are still my first choice.
I have replaced a great many failed modern relays but have replaced very few of the old relays which are decades older.

There are many types of parts I replace proactively. Relays are not one of them.

 

Excellent feedback, thank you both. My 80s Bentley uses the same Bosch metal relays (a few dozen of them) and all are original to that car, for what that's worth. I'll grab a couple spares and leave the metal ones installed.
-Mike

 

Correct.

 

For me also; I prefer the metal ones. As I put a alu sheet against them to spread the heat....

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The metal ones will allow more heat to exit from the internals. Plastic is a poor thermal conductor. Metal is a good conductor. Heat must pass through the enclosure to get out. Besides metal being a better conductor of heat than plastic, the plastic is always thicker than the metal exterior compounding its resistance to heat passage. The hotter the internals of a relay, the shorter the life expectancy.

 

I replaced all my metal ones with the plastic ones about 10 years ago, and yeah I've had to replace a few of the plastic ones for specific often use circuits like cold start, headlight lifters, horn.
I also built this fuse box cover with a built-in thermostatically controlled fan, I built it out of an old broken cover, hence the zip ties holding it together, LOL!
I also also installed the fuses that light up when they're blown, you can see one on the top right of this photo.
I also put in a direct plug-in for my battery charger on the right side. But I usually just run without a cover, since the area is weatherproofed anyway.
Alden
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Interesting, first evidence I have heard that the newer plastic relays don't last as long as the original metal cased ones. I am surprised, as relays are not that complicated a product. Must be lower grade copper, too thin copper windings, which is where much of the raw material costs would be.

 

I almost never used to replace relays. Now I keep 50 or so in stock. Especially those pathetic micro relays.
When you say you are surprised, can you name a single automotive electrical component that is higher quality and more reliable now than in the late 80's or early 90's? I cant. Even the harnesses are junk in comparison. Its been a huge area of cost cutting just when the cars are more dependent on it than ever.

 

When I've had a problem with my car, the first place I go to is the relay associated with that circuit, if it has one. That's almost never failed to solve the very few problems I've had with my car.
That, and good regular preventative maintenance and a recent major have kept my car reliable and trouble free for 10 years.
Alden

 

Interesting. All the relays in my '85 QV are original. Never been a problem in 40 years.