New to me 98 2500 CTD 12v QC 4x4, blah, blah, blah...

Temp guage hasn't moved yet (owned this truck less than a week now). Before I go digging - is this a "normal" failure for these trucks, and if so - is it generally the sending unit, or the guage? Thanks for any help

 

I would change out the sending unit first as this is the easiest. While you in there (or while your changing the sender), check the wiring and the connection point. Might just be corrosion. But if your gonna change the sender, and the truck is new to you, go ahead and change the coolant. The few bucks and extra time will give you peace of mind. Personally, I would change out all the fluids if you don't know when it was changed before. Sounds like a nice truck, the 98 12 valves are the "holy grail" of the 12 valves. Consider yourself lucky to have one.

BTW, when you have the temp gauge working, it is normal to see the gauge "swing" or "cycle". Meaning, it contantly moves up and down while at operating temp (slowly of course, but you can see it). Good luck, Kevin

 

Before you throw parts and money at it, here is a simple and free check to see if it is the sender and guage. This is based on prior expierience with my F150 and it worked well with it.

Disconnect the wireing on the sender unit. Turn the truck on or start it (doesn't matter, so long as the instrument panel and electronics have power). Leave the wire hanging in the air not touching anything. The guage should read cold. Now touch the wire to the engine block or nearby piece of metal. This should cause the guage to swing to hot. (I may have that backwards, however opening and shorting the circuit will cause the guage to move one way)

Hope this helps.

 

Thanks guys


Someone on another board mentioned that I may be wrong after all - and the fact that the heater output sucks in this thing right now may mean the thermostat is the problem - and is why the guage is not reading anything... Thoughts?

 

Even with the thermostat on the fritz, you should have "some" reading on the gauge. Mine went a couple of years ago, and wouldn't get into the normal range. But the gauge still registered some temperature increase.

 

Ok, think thing is confusing the heck out of me.

I noticed on the drive to work this morning, the temp guage did move up above the 140 mark, but was not into the "normal" operating range. I did notice it fluxuating - which I was told it will do.

Where is the sending unit located so I can test it as described? Thanks...

 

It is on the drivers side, top/ rear of head,just under the lifting bracket,a black bracket used to lift motor or head. One more thing,I do not know how cold it is where you live,so you might try to add a piece of cardboard between the intercooler and radiator and see if it will come up to operating temps. Do this if it is under 45 deg. I have to agree with the idea of changing out all of the fluids also. Goodluck Rick

 

I've seen temp senders come unplugged or barely connected quite often in the struggle to replace the fuel hoses or change the fuel filter. Easy check, top right.

 

Sweet - that helps!

Kinda confusing as the previous owner installed some kind of remote fuel filter up top that hids a lot of what is under that side of the engine.

And possibly unrelated - was poking around under the hood Sunday afternoon and found some wires that look like they have pulled out of a sensor or had been broken. No clue what they go to - gonna have to pick up a manual of some kind so I cna trace wiring and see.

 

No worry on the disconnected plugs.
I can think of at least three under the hood
and four under the dash of my '95 that either
aren't used or are computer test ports.
There is one right on top the engine by the
injection pump that is unused and easily noticeable.

 

Ok, It keeps getting stranger

Took the truck on a nice 2+ hour drive out of state this weekend, and the temp guage DOES seem to come up to the "normal" range when the outside temp was a bit warmer than normal.

Which leads me to ask - what is "normal" operating temps for these vehicles? Maybe it was just too cold the last week otr so for the vehicle to get up into the "normal" range?

I am even more confused than before

 

Going down the road, my truck stays right at 190. Since you are getting readings on your gauge and complain of poor heat, I would guess that your problem is T-Stat or antifreeze level. Due to the mileage on your truck, I would start with a good flush and fill of the cooling system and replace the thermostat. Make sure it is properly filled and bled and I would guess your problem will be gone. Assuming no leaks or antifreeze useage.