1997 dodge ram b3500 van.5.9L
First off ill start by saying here are the parts ive replaced so far. New radiator, 195° thermostat, coolant temp sensor, radiator cap, heater core and new coolant

Secondly!
So my temp guage does not have number markings in degrees or of any form at that. It's just solid white lines in 1/3rd increments. I have uploaded a picture for you to see, as well as color specific indication lines for u to reference what i'm explaining here. Green,yellow, and red.. hence why I'm confused on this subject with there being no temp numbers.

My question is regarding the temperature fluctuations.

Most days and most of the time it runs (fully warmed up) below the first 1/3rd mark. (Green line).. Then sometimes I'll just happen to glance down at the guage and see that it's reached more towards the halfway point. Sometimes it will barely be past the 1/3rd mark (yellow), and on hotter days it can reach up to the center in the middle (RED) with OR w/o ac running (altho with ac running on a hot day it will STAY at that mid section were red line is, until I turn heat on full blast then it moves down to yellow line) The weird thing is, idling stationary in traffic vs driving 65mph freely on highways has no evident effect on this since I've seen the needle fluctuate while stopped in heavy traffic as well as traveling freely with NO traffic. Ambient Temps have an effect ofc on hot days it runs hotter, cold days runs cooler. Even in 3° cold weather , it will reach toward yellow line. Seems like it should stay at green?

I am trying to figure out if this is a normal occurrence for this 5.9l engine. And how can I tell if it's running hot if I have no numbers to go off of and no temp lazer gun? So correct me if I'm wrong but I would assume that If the needle is in the green position, that's likely normal operating temp with no load. (193-205?) And as the needle moves to yellow and red position It means it's getting hotter towards 210-220+ ?? Overall, I'm curious: Is temperature fluctuation normal in this van? Or am I having a new part partially failing on me? COULD this be a side effect of a leaky plenum? That's the only thing I have not changed. Or am I overthinking this? Everyone's car I've ever test driven or borrowed to drive, their temp needle gets to operating temp and STAYS there regardless of ac being on or off. In my head, the cooler it runs, the better. Hot means bad. I've never had it reach hotter than the red line that I drew on this picture. the halfway point.

I also read that a clogged CAT can cause this if exhaust fumes arent exiting the pipe effectively. Thats a whole other process i havent got into yet. Any explanations or help troubleshooting /advice / upgrades would be appreciated. And also if anyone could reference my color coded lines to a temperature in degrees Ferenheit. that would help me understand the temp ranges I'm experiencing. Is this temp fluctuation harmless or something I should dig deeper into fixing. Thank u in advance!

Sincerely,
Paranoid Floor installer 😅

 

Plenum probably is not related. I expect to see some temp fluctuations as the engine warms, but, once it is up to operating temp, it should be pretty steady. Now, if load on the engine changes, like climbing a hill, or something similar, I could see temp climbing a bit...... Would be interesting to see what the PCM thinks is going on though. And what temp is actually doing.

Your van has two temp sensors. A one-wire sensor for the gauge, and a two wire sensor for the PCM. Which one did you change?

 

I changed the one next to the thermostat. I beleive it was one wire and a plug. I could be wrong tho. I'm not sure which one it was. actually had no idea there were 2. Should I change the other to be safe? Is there a way to hook up a scanner while I'm driving and read live Temps in real time?

 

The right scanner will read real time data. As for which sensor is where.... that was one of those things dodge just couldn't make up their minds on.... On my 96 5.9 (truck), the two-wire sensor was by the thermostat.

 

The thermostat could cause that issue and being brand new doesn't rule it out. My 96 5.2 normally runs where your yellow line is.

 

HeyYou, do u think you have an idea of temp ranges for this guage of mine? I have a picture from another forum that said this guage was from a 97 b3500 as well, ours are different tho? My question is, is it safe to assume the ranges are the same? Like his 200° in middle would be the same as mine? I'm having trouble finding any info on this and don't have a scanner. Here's a pic. Our guages don't have the same layout, but Would my Red line on My guage be 200° since it's in the center? The pic I originally uploaded is my actual guage. The second one I upload with this post is the guage I found from another forum. Said it was a 97 3500 guage.

 

Good question.... I don't know though. So long as your is staying in the 'safe' range, things are probably ok. If there is one of the big chain auto parts stores within a reasonable driving distance, they should have a scanner that can read some live data at least. See what the PCM thinks engine temp is when fully warmed up, and where the gauge is reading.

 

So I have some live data here. The scanner showed Temps of ECT & IAT.

Edit: found out it stands for Engine coolant temperature. That sounds better.

So my first 1/3rd mark (in between green and yellow) the ECT reads 200° F. This is normally what it runs at all the time, give or take a hair, & i was idle at the time. My new radiator keeps it there much easier when driving, and with AC on. The old radiator had tiny leak which would explain the re occuring temp rise every now and then. And the steady running hot with ac on. That seems to be fixed and no longer a problem

altho , even with new radiator, I've noticed for the first drive of the day it will spike to the halfway mark (red line on my drawing) after sitting cold all night. so I'm guessing it spikes to that higher temp before Tstat has time to open all the way? Once the Tstat opens tho it remains at that 200° area, yes even with ac on max (seems too good to be true so not an issue any more, i see that as a great improvement) im still curious about the initial temp spike at first, could I have a slow tstat? Or is it pretty normal for Temps to spike before stat opens? I am staying in the safe zone, just worried about warping something. If this sounds normal I'll consider this issue resolved, since new radiator seems to be doing a good job. And again. It will spike but then take about 3 seconds to get back down to the 200° mark. So it doesn't stay there for long at all, also only does this on first drive of the day.. Harmless? or is there more to look into? Thank you for all of your knowledge.

 

Here are a few pics , I was able to catch a video of it spiking this morning before quickly falling down. Video is shakey so I took some screen shots.

 

Sounds like normal behavior to me. The initial spike when first warming up is not unusual. Temps are good as well. I think you are all set.