Relay overheating?

[l3n]

Quick question for the wiring gurus: could excessive engine compartment heat kill a relay?

I have a thermostat dual fan controller relay installed, with one lead going directly to an electric fan, and the other lead going to a separate relay connected to an electric water pump. After a couple of weeks, the relay somehow fused itself open (or closed?) so that it's now constantly on. It shouldn't be a matter of excessive current draw, since the controller is only powering a fan, with a separate relay for the pump, right? The fan's current draw is within the limits of the controller.

The reason I'm asking about engine heat is because I'm still fighting an exhaust leak that's strong enough to vapor lock the carb, and I noticed that the heat shrink on the wiring terminals have started to wrap themselves around the ends of the terminals too, which would seem to indicated the compartment is getting pretty toasty. Could that heat have also knocked out the fan controller? I have a spare that's half installed, but I don't want to push my luck til I get this figured out.


Thanks fellas.

 

[Mercury Mike]

First things first, pull that exhaust manifold out and get it sealed correctly!!!

 

[BIGREDRASA]

First things first, pull that exhaust manifold out and get it sealed correctly!!!

10-4

 

[l3n]

Brother believe me, I'm trying.

I just found out about the 3x retorque rule, and upon checking, the manifold bolts were indeed loose again, so I recranked them. Hopefully that'll fix it. I'm still waiting for Mike's shorty headers to return, that's my final goal for exhaust. I'd have gone and bought the Clifford's already, if it wasn't for the fact that the newspaper biz in SoCal is on the verge of collapse, taking my bank account along with it. Momma, don't let your babies grow up to be newsmen...


Aside from that though, could an exhaust leak generate enough heat to cook a relay?

 

[Mercury Mike]

Yeah. Get that heat outta the engine compartment and keep it inside the manifold! That's why we blow it out the back. =) hahaha. I'd just spend a day gettin' it in and out properly.

 

[Bort62]

Aside from that though, could an exhaust leak generate enough heat to cook a relay?

Yes. Electronics are extremely temperature sensative, even electro-mechanical devices like relays.

The typical temp rating for something like that is 80* C, which is pretty hot... but if it's close to the exhaust or is getting strong radiant heating otherwise, it could certainly acheive that.

 

[rbohm]

8) what amp relay are you using, and is it rated heavy duty and or constant duty? and yes heat can affect relays by reducing the amount of amperage that the relay can handle. for example a 50 amp relay wont handle 50 amps constanly when the underhood temps get above those allowed by the relay.

 

[l3n]

Thanks as always for the info guys.

The controller is a Derale 16748 rated at 25 amps.

http://www.derale.com/adjust-fan-controller.html

The pump relay, which is triggered by the secondary lead of the fan controller, is from Stewart Components, and is the suggested relay for the electric pump. (Yeah, I'm one of the guys who bought the $350 Stewart pump. With my setup, it was one of only a few options).

http://www.stewartcomponents.net/Mercha ... gory_Code=

http://www.stewartcomponents.net/Mercha ... =ElectPump

The fan is a Spal, rated at 18 amps, which is pretty close to the limit of the fan controller. That's why I hooked up the second relay, so that the secondary fan lead is just a trigger and shouldn't draw any significant current....right?

 

[l3n]

Yeah. Get that heat outta the engine compartment and keep it inside the manifold! That's why we blow it out the back. =) hahaha. I'd just spend a day gettin' it in and out properly.

My plan is to spend tomorrow slapping a few coats of high temp paint on her, to try and cool things off a bit until Mike's shortys are ready.

 

[JOHN G]

What size wires are being utilized-if the guage is too small, it will cause the relay to heat up as well. combine this with the underhood temps and it could amplify the problem. Make sure the trigger is sufficient as well. Heat is the number one destructor of electronics.

 

[Bort62]

What size wires are being utilized-if the guage is too small, it will cause the relay to heat up as well. combine this with the underhood temps and it could amplify the problem. Make sure the trigger is sufficient as well. Heat is the number one destructor of electronics.

Insufficient wire gauge will not heat up the relay, only the wire.

 

[l3n]

That's what I thought too (woo hoo! I knew something this time!), but the wires are pretty fat anyways. 10G power leads, and 12G triggers. The only thinner wires in the circuit are built into the controller, and I'm guessing (hoping?) that they know what they're doing.


So far, retorquing the manifold bolts seems to have cured the leak, far as I can tell. The headers are still cooking my engine compartment though. The manifold paint job hasn't helped it quite enough. Might try pushing the timing back and richening up the carb I guess...

 

[JOHN G]

The relays coil latches with a minimum amount of current-if that current is at its lowest point, the coil will develop more heat. If the wires get hot from insufficient guage, where do you think the heat may go as copper wiring is an excellent conduit? The heat will not just stay in the wires, but will travel into the relay as well and that may cause a failure. Any and all electrical devices with a coil will develop heat as a byproduct and certainly adding to it with extreme engine temps will not help it. Do you have a clamp-on meter that you could measure the current draw with? That would give us an idea of how many amps are being used to power the relay as well as tell how much current is being pulled through the relay to the switched device. Excessive current draw will heat things up as well. The fact that the wires are melting right at the relay says that this is the hottest point-the wires are solid untill they enter ther relay contacts which creates a resistence point(hot spot). Just my 2 cents in the end, but I have wired thousands of relays for automotive apps-hopefully I don't come of in the wrong way-just trying to help

 

[l3n]

The relays coil latches with a minimum amount of current-if that current is at its lowest point, the coil will develop more heat. If the wires get hot from insufficient guage, where do you think the heat may go as copper wiring is an excellent conduit? The heat will not just stay in the wires, but will travel into the relay as well and that may cause a failure. Any and all electrical devices with a coil will develop heat as a byproduct and certainly adding to it with extreme engine temps will not help it. Do you have a clamp-on meter that you could measure the current draw with? That would give us an idea of how many amps are being used to power the relay as well as tell how much current is being pulled through the relay to the switched device. Excessive current draw will heat things up as well. The fact that the wires are melting right at the relay says that this is the hottest point-the wires are solid untill they enter ther relay contacts which creates a resistence point(hot spot). Just my 2 cents in the end, but I have wired thousands of relays for automotive apps-hopefully I don't come of in the wrong way-just trying to help

No worries man, I'm here to learn, and you're giving me information. I appreciate it. I'll readily admit to being one of the least-knowledgeable folks around. But I read the boards almost every day, and I learn something new every time. One of these days I'll be up there with the rest of ya

The thing about heat traveling up the wire makes sense, but it's not the wires that are melting, it's the heat shrink tubing around the ends of the terminals. The wires themselves aren't turning color, or getting stiff, or showing any other signs of trouble, so I figured the heat was coming from the outside, not the inside. Does that sound right?

The weird thing is, the termostat gauge isn't getting all that hot, if anything, since I installed the new cooling setup, it's running colder than before. So I think all this heat has to be coming from the exhaust manifold. Since I got the leak fixed, the vapor lock appears to have disappeared, but I'm still getting heat soak on the starter, which makes me fear that the new controller relay is going to get hosed too. Very annoying.

 

[Bort62]

True, heat will conduct up the wire to the relay, but If your wire is hot enough to have any negative effect on the relay, it's going to have long-since burnt off all it's insulation.

 

[Mercury Mike]

Make a heat shield for the headers or around the starter. Let it soak up the heat. =)