Engine/Transmission (1994 - 1998) Pre heater part II problems ? ?

[Jeff H]

If you have been following?

OK I was able to install a used thermo sensor on the old pre heater. I used the new used wires and connectors. I started up the truck and let it idle for about 20 minutes. I then checked to see if all was ok. I noticed some smoke coming out of the thermo sensor. It was very hot to the touch. Now I'm lost again. Is this gonna be ok? I don't think this is good. I did put some die electric grease in the connectors. Is this gonna be a problem?

My relays do go on and off with the ignition switch.

 

[SMorneau]

Sounds like your sensor was bad, or at least it is now. I don't knowif the grease on the metallic connections is bad or not but at most it should have created an increased resistance that would reduced current thru the thermo sensor. If that resistance were going to cause a problem it would be at the point of increased resistance where the grease was placed, assuming the grease may cause an increase in the first place.



Are you sure the sensor was the point of origin for the smoke? The relay should switch off and on with the ignition so that is working ok. The sensor is the on and off for temperature. It should open the circuit at 80F and close the circuit at 40F. The manual says the fuel heater element should read less than 1 ohm cold and up to 1000 ohms when warm. If you need a meter to check it I can let you borrow a small one I have at work. I'll leave it out for you if you shoot me a mail at work.





The manual also states the fuel heater needs a minimum of 7 volts to operate. I am not sure what they mean by this. I wouldn't think low voltage would damage anything.

 

[Jeff H]

Check and test.

Hi Scott

I'm Quite positive about the smoke coming from the sensor. I shined a flash light right on the sensor. Its a slight amount though. But seamed to get worse the longer I ran it. It was also very hot to the touch. I think I may have a bad heating element already. Just has not work since I had Mike Install the new element a few months ago.

I checked the voltage with the motor running. Checked at the connection for the pre heater. Reading around 11. 5 volts. At the battery I get 12. 5 volts. So some where its drawing some voltage.

I stopped up at Zips today. He usually replaces the whole works. He has seen many melted connections that come into the shop.

He said I should just turn the key on no motor running. The fuel should heat up to 80 degrees. Then the pre heater should shut off. Looks like I'll be doing some more testing Friday. I do have a multi tester. Can't live without it.

Since I've been working on this issue. I've really think Dodge did a not so good a job of wiring this up. The wires from the relay are so much small than the wires on the pre heater connectors. That alone you would think would raise the resistance. Then the way they routed the wires through to the fire wall. I can't believe there has not been a lot of electrical fires.

I think a slight rewire will be in the future for the pre heater. I'll have to take a look at yours Scott. But I want to add own temp switch. A switch thats off anything above 15 to 20 degrees. I think 80 degrees is way to execive to shut it off. Also I would think if it ran less the pre heater would last longer.