Engine/Transmission (1994 - 1998) Pre Heater Had A Meltdown ? ?

[Jeff H]

I discovered some melted wires today on my pre heater. The top connector is completely gone. The bottom connection looks ok. Whats going on? Earlier this fall I had the heater element replaced. We started seeing cold temps this week. So I suppose it kicked on.

Is there a relay that operates this thing?

Is it the temp sensor involved also?

I think if I get it fixed. A fuse will be added. Don't want a Car-B-Que with me in it. Right now its completely disconnected. I may just leave it that way too. I've never gelled in the 6 years of driving this truck.

I could use some education from somebody how this thing is wired.

Thanks Jeff.

 

[C. Harlan]

maybe it is sticking on, and not cycling on and off... that is what it seems like to me. . I am sure Bill Fleming will chime in, as well as someone else. . But in my opinion, it sounds like it is not cycling off... May need to get that checked out!



-Chris-

 

[illflem]

The heater goes on at 40° and off at 70° so it is on quite a bit. Only problem with having it disconnected is if the temp drops below zero. Even though your fuel doesn't gel wax particles will start to form and can plug your filter. This will happen slowly giving you time to get aways from home before dying. No fun walking when it's below zero. Think the parts to totally rebuild the heater are under $75. Could be worth it if you live in the northern states.

 

[bmoeller]

The relay that controls the heaters could be sticking on.

 

[JohnE]

Jeff;



Bummer on the fuel heater especailly after getting it swapped in September to fix a leak.



Scott had the same trouble on his 96. I don't remember the true cause, but I think it was the connector.

Loose connections or ground points are usually the biggest troubles in heavy amperage or high use circuits.



-John

 

[SEmerson]

I had the same thing happen before. It was the relays sticking. I replaced them with 2 ford starter relays.

 

[Deezul1]

SEmerson



I hope your experience with starter relays is better than mine. I found out the hard way that starter relays are designed for momentary usage and wont last long when activated for longer periods. I tried using one for a batterry isolater for a RV battery when it was required to stay on for long periods. I dont know how long these heaters are needed to stay on though.

 

[Jeff H]

Well the top connector is completely gone.

There is an open spot on the wire. But it was touching a hose. Don't think that would short it out? But maybe?

Well I will check it out next week sometime?

AT least my new block heater and magnetic oil pan heater works good.

 

[QRTRHRS]

Relay Replacements

If it is the relays, check this out. http://www.alliedelec.com/cart/partlookup. asp I went this route based on a thread that I don't have anymore. Cost is 1/3 of the dealer. You need to make a bracket because they are larger then stock. If you look down along the drivers side inner fender, you can see how the stock mounts on the flat bracket. I made a "U" shaped bracket and laid them parallel to the fender. The cables lay against the bracket rather then the selenoids.

 

[QRTRHRS]

Sorry, the search lead did not work. Type in Allied part # 576-3008 for Stancor part 120-902.

 

[illflem]

Isn't that the relays for the grid heaters rather than the fuel heater anyway?

 

[QRTRHRS]

Originally posted by illflem

Isn't that the relays for the grid heaters rather than the fuel heater anyway?

Your right, I did not read the original post thoroughly.

 

[C. Harlan]

A little off subject.. live with it.

Hey QTRHRS... . just wanted to let you know you and your family are in our prayers!



-Chris-

 

[SMorneau]

Jeff I had the same thing happen to me. Here is what I can tell you.



The amperage of the circuit is high enough by design to generate significant heat at any resistances in the circuit. When the connections start to get a little oxidized the resistance goes up and heat is generated at the connection. If the connection isn't designed for the heat it will melt.



While there is no fuse I believe the circuit is on a "fusible link" at the battery connection. This does precious little good at preventing meltdowns because the current that is melting your connectors is withing design limits for the circuit.



The off and on switching of the heater is controlled by a relay that energizes when the truck is running with the ignition on. The actual swithing based on temperature is done by a thermal switch that is mounted to the top of the prefilter housing. If the relay is stuck on the heater will be working when your vehicle is parked and the batteries will eventually run down. If the thermo switch is bad it could stay open or closed or just "pop" at the wrong temperatures. Neither the switch or the relay is responsible for your meltdown.



My biggest concern with this circuit was the routing. A high current circuit running thru the harness that goes up over the engine to the firewall seemed kind of risky. Should a meltdown result in a short I could imagine the whole harness getting melted and requiring major work to repair.



Because of my concern, I added another relay mouted on the fender well that is switched from the factory lead that originally ran to the heater. The relay I added is swithing power to the heater via a fused lead from the battery. My only concern with my new arrangement is the possibility of my relay failing with welded contacts which would leave me with dead batteries.



When I re-connected the leads to the fuel heater I used some of the Posi-Lock connectors that should stand up to heat. I also sealed everything really well to try and reduce oxidation and prevent the problems in the first place.



I never replaced my heater or my harness (although I have the heater ready to go) because they showed no signs of generating heat. Only my connector at the end of the thermstat harness was melted.



Bottom line is this. If you decide to redo the existing circuits you have to use a connector that will be reliable and stand up to the heat.



I shoot you a PM with my home phone in case you want to talk.

 

[Scot]

Originally posted by SEmerson

I had the same thing happen before. It was the relays sticking. I replaced them with 2 ford starter relays.

Try the Standard Ignition SS496 relay. It looks a lot like a Ford starter relay except it can be triggered by either the (+) or (-) wire. It is rated constant duty. They are used on winches and such.

 

[Jeff H]

Thanks Scott

I would have to say oxidation was a reall problem. My old batteries made a real mess. I had to wire brush a lot of wire connections after I installed the red tops. I never did think about cleaning the fuel heater connectors.

I was sorta looking at maybe putting an aftermarket fuel heater on. Either an inline heater. Or a heated fuel line from the tank to the lift pump. But I think an inline will be sufficient. If cost justifies it maybe? Oh it made by Racor.

 

[krs]

I'm not sure that this will help solve the problem but at least it indicates that the fuel heater is in a 40 amp fused circuit:

http://dodgeram.info/tsb/recalls/cust_notice_770.htm

 

[dremelts]

The little thermostat on top of the fuel prefilter burned up on mine last year and, although it is easy enough to replace, it got me to wondering how you would ever know whether or not the fuel heater was actually functioning. I mean, if I had not actually seen the smoke coming from that area when it burned I probably would have gone the rest of the winter without a fuel heater or, at least, until the fuel gelled and plugged the filter.



I have thought of wiring a shunt inline with the heater element with some sort of light inside the cab that will indicate when there is actually current flowing thru the heater element.

 

[Jeff H]

Lucky me. I stopped down at the local auto salvage yard. I found a used pre heater with a good connector. I saw this pre heater when I was there in July. It was still there. Also scarfed up other engine related parts.

 

[SMorneau]

All of the connections must be in A1 condition in this circuit or they will melt.



I also thought about an indicator light but I couldn't come up with a good way to make it indicate the actual element was functional and heating. I think you would actually need to put an ammeter into the circuit. Even then the reading would vary because the resistance varies with the temperature (IS that right?).



Jeff, does that junker have a steering wheel? I was thinking of getting my leather cover replaced and it would be easier if I had another wheel. I could then offer it as a pass around loaner to others who wish to do the same. I think the news ones are kind of pricey.



Does the junker have an engine? Are these people giving you good prices on parts?