Relays. Which to replace?

[Pags44]

Hey guys,

I'm debating whether or not to replace some of my relays. I know that about 5-10 years ago the previous owner had done a relay update kit. Now I know there are now two kits from DMC, the relay update kit and the relay update kit (improved).

I currently have some metal Bosch cans in my D. Are these worth replacing or are they rock solid because thurs German Bosch cans? Please see pics for reference.

Reason I'm looking into this is because I saw my yellow jumper wires stating to melt. We've come up with a solution for that since it seems that replacing them doesn't fix the problem. My mechanic is going to install relays at the fans and use heavy gauge wire to go back to the box. So I believe that should solve that problem.

[DavidProehl]

I'm guessing your relays are fine if they are only 5-10 years old. I personally wouldn't replace them.

I don't like the idea of running a new wire for the fans. The stock wiring should be able to handle the load unless your fans are going bad on you or you have bad connections somewhere in the circuit. Have you tried replacing the pins on the fan socket or looked for corrosion/bad crimps?

I've seen enough threads dedicated to previous owner re-wiring messes to know how quickly a work around can cause other problems if not done carefully or not well documented.

That is my vote for what its worth. :)

[David T]

Instead of rewiring the car you should look at the options available to replace the fan fail relay jumpers. Pretty much "plug and play" so it might be cheaper (no labor). As for the relays, if you have the upgrade kit installed I would leave them alone. If everything is working and there is no heat damage all you might want to do is keep an extra relay handy and a jumper wire just in case.

[Bitsyncmaster]

If your jumpers or fuses are melting, that pretty much says your fans are drawing to much current. The jumpers use 12 AWG wire already. Don't use BUSS brand fuses. Little fuse brand looked good with my testing.

[Pags44]

Forgot to mention. This is a low mileage car, under 5k, that had undergone extensive restoration with all major systems replaced...except the fans. Just installed a new DMC 3-core radiator last month. We think the fans may have been replaced at some point, but the prior owner didn't do it.

My mechanic thinks the distance in the wire is too much resistance and that's why they keep melting. He's done this wiring the relays to the fans on other cars of the era with success. I've seen other posts on here where others replace the jumpers and they keep melting over and over, regardless if they're part of a new, or improved, DMC relay update kit.

Does any of this change opinions? Thanks.

[DavidProehl]

Does any of this change opinions?

No. Since your fans are original this probably means they are getting old. Running a wire might fix the melting issue now, but in a couple years when the fans finally die you will be replacing them anyway (and if your are unlucky, overheating your engine). The point of those jumpers with the fuses is to blow when your fans start drawing too much power. It seems that is what your fans are doing, but the fuses aren't blowing like they should. Replace the fans.

[Pags44]

The wires are melting at the connector. That leads me to believe there's a bad connection there instead of the fans but it could be one or both couldn't it. It pains me because those fans look brand spanking new. My mechanic's idea was to mount relays at the fans themselves to isolate it.

We're going to test the fans to see what they're drawing. Any idea on the best way to do that?

I believe drawing more than 8A per fan is too much? Is that the magic number?

If the fans are bad, what are your recommendations for good ones? DMCMW did not recommend using their new replacement fans because they move less air. I saw that DMCNW looks to have some improved fans...

Thanks again for the continued support!

[Bitsyncmaster]

Use the clamp over the wire type of amp meter. I think good fans draw 10 amps or less. Most of the vendors low power fans run about 7 to 8 amps.

[hmcelraft]

The source of power for the fan circuit is one of the weak spots (it comes from the gang-connection behind the backboard of the package tray). In addition, the single low amperage OEM relay is also too weak. If the fans are cycling with the AC compressor the amperage draw goes up to approximately 18 amps to start each fan motor - that's 36 amps per start. That adds a lot of heat to a high resistance circuit.

If you stay with a single relay fan circuit, you should get one of Hervey's 50amp relays and a 40 amp circuit breaker. Then source power directly from the battery and check the grounds of the fans at the front of the frame. You might check the connections in the washer bottle compartment. It's not unusual that those connections need servicing from time-to-time (cleaned and contact protectant put on them).

BTW - what wears the fan motors out is lots of starts. Constant running allows for much more life from the motors. Especially when they receive full electrical power.

[DMC-81]

Forgot to mention. This is a low mileage car, under 5k, that had undergone extensive restoration with all major systems replaced...except the fans. Just installed a new DMC 3-core radiator last month. We think the fans may have been replaced at some point, but the prior owner didn't do it.

My mechanic thinks the distance in the wire is too much resistance and that's why they keep melting. He's done this wiring the relays to the fans on other cars of the era with success. I've seen other posts on here where others replace the jumpers and they keep melting over and over, regardless if they're part of a new, or improved, DMC relay update kit.

Does any of this change opinions? Thanks.

With only 5K miles, and a suspected fan replacement, I would check for good ground and clean/check the terminals at the connector. Then, if the problem was still there, I would suggest disassembling the fans to clean and check for wear. Especially if you don't want to get a different set. Of course, YMMV.

I had great luck refurbishing my OEM fans (they had 26k miles but worked intermittently). They were just dirty inside and had surface rust on the case. Afterwards, they run like new and have cool wires.

44471

Good luck.

[Pags44]

Just went over all of this with my mechanic. Thanks for all your knowledge and opinions. For now, were going to hold off on mounting relays at the fans themselves and focus on the melted jumpers in the box. He thinks when the original relay update kit was done the connectors were damaged so he's going to crimp them together to reduce any possible resistance there. He says the fans look brand new and doesn't suspect there will be any problems with them. Thoughts?

Also, I know the fans seem to be a problem item on our cars but is it because of this issue with the fan fail jumpers? Or is it the fans themselves?

Looking for the fix that will make the fans bulletproof so I don't have to worry about possible overheating. I see all sorts of aftermarket parts discussed like Fanzilla, DMCNW Wings-B-Cool upgraded fans, etc. Thank again.

[DMCMW Dave]

My mechanic thinks the distance in the wire is too much resistance and that's why they keep melting.

.

Your mechanic doesn't understand ohms law. More resistance in the wiring will not heat up the connections. It will, in fact, lower the current.

[Bitsyncmaster]

Looking for the fix that will make the fans bulletproof so I don't have to worry about possible overheating. I see all sorts of aftermarket parts discussed like Fanzilla, DMCNW Wings-B-Cool upgraded fans, etc. Thank again.

None of the fan controllers will solve a high current fan problem. We don't have failure data on any of the new low power fan motors but quite a bit of failures on the OEM fan motors with high current and actually failing.

As Dave S pointed out, lower voltage due to resistance of long wire runs reduces the current in the fan circuit. So bad connections do not increase current but reduce it. The bad connection however will produce heat right at the bad connection.