Used Truck w/ Problems

[Northrunner]

After about a year of looking and learning about trucks, I finally bought a '98 12v 3500 dually with 86,500 miles on it. It appears to be stock and in great shape, but it's got a few things that need to be fixed.

1. The factory temp guage only occasionally moves off the 140 degree mark. What's the problem there?

2. The factory fuel guage will read correctly, then drop like a rock to empty, the fuel low warning light will come on and start dinging, then the needle will fly back up to read correctly and all is normal. Then 4 minutes later it starts all over again and then all is well for an hour, then it starts again. What's up with that?

I have learned a ton about these trucks during the last year from this web site. My thanks to you all for sharing your knowledge.

 

[LSMITH]

I don't really know the answer to either of your questions, but I can welcome you aboard. I would try taking the thermostat out and replacing it first, just a couple of bucks and might take care of your problem. The fuel senders are a known problem, you can do a search on them and get months of reading.

 

[Todd G]

Sounds like the thermostat is stuck open. Get a new one. My fuel guage is doing the same thing. I just bought a new sender from Dodge for $60 bucks. This is a very common problem on both counts.

 

[Deezul1]

Welcome to the group, My 96 did the same thing on the temp, outside temp was 55 deg and the gauge barely moved at all new thermostat fixed it. The fuel gauge prob is considered normal on these trucks, if you have one that works correctly you are in the minority. Easy way to replace it is to remove all the bed bolts except the back 2 and tilt the front up for clearance dont forget fuel filler and wiring disconnect. way easier than dropping tank.

 

[PCline]

Your fuel gauge problem is due to the sending unit in the tank going bad. Don't spend the money to buy a new one though. The fix is so easy and cheap (cost 49 cents).



Here's how you do it. Following your manual to get the fuel sending unit out of the tank. This is the hardest part since the tank straps are very difficult to get off and the "Big Platic Nut" on top of the sending unit can be a bear.



Once the unit is out of the tank (it's big by the way) find were the float hinge is. You will find an electronic brush that moves along a variable resistor. The problem is that the plastic bushing has worn out and allows the brush to move away from the resistor (infinite resistance and therefore the light on the dash lights up).



Remove the pin and the float hinge joint and drill the hole slightly oversize. Replace the pin with a small bolt and screw. Make sure to use a self locking nut. Tighten the nut only enough to prevent freeplay in the joint but so much that it restricts movement of the float.



I did this to mine about a year ago and its still working fine.



Good luck.