Engine temp fluctuation

[Nathanielgass]

I replaced my thermostat and eventually water pump aft the truck but now the temperature gauge (which I believe to be accurate) fluctuates from the hot side of the safe operating range all the way to the cold side. The coolant system had a small mystery leak, which a mechanic told me is my radiator, which I need to replace. He thought that might be causing my temperature issues. But after leaving the mechanic, it’s no longer really using coolant, but the large temperature swing persists. After I’ve been driving 30 minutes or so, the temperature steadies out. Any thoughts on the temperature issue? The truck has this issue before steadying out whether loaded or unloaded.

 

[Timd32]

New vehicles the number is calculated in the computer and it never really swings. Maybe 98.5 and up, someone can chime in on that.

Older vehicles it's pretty accurate of what the system is actually doing in real time.

My 96 swings 190ish to cold all day, I don't tow much, but what you described sounds normal to me.

These 6BT are just really built correctly and have excellent cooling systems, watching them work is part of the fun of having an older one. I would imagine on the right road and ambient temperature you could set your watch to it.

Good luck with the truck.

 

[Nathanielgass]

New vehicles the number is calculated in the computer and it never really swings. Maybe 98.5 and up, someone can chime in on that.

Older vehicles it's pretty accurate of what the system is actually doing in real time.

My 96 swings 190ish to cold all day, I don't tow much, but what you described sounds normal to me.

These 6BT are just really built correctly and have excellent cooling systems, watching them work is part of the fun of having an older one. I would imagine on the right road and ambient temperature you could set your watch to it.

Good luck with the truck.

thanks fir the info. I’ve been reading that temperature fluctuations are normal, but I think this may be more than normal? It cycles every minute or so. I’ve been driving the truck for three years now, and it used to very slowly creep up toward operating range and just sit there without moving. The thermostat that came out was a different design- it was cylinder shaped with holes punched in the back instead of a flat disk with the spring sticking out.

 

[BigPapa]

The temp fluctuation is normal, don't worry about it. The radiator sounds fine to me. When the thermostat opens it cools down from the sudden rush of cool coolant from the radiator, the thermostat then closes and it starts all over again. If the radiator was clogged it wouldn't cool down so quickly.

I would suggest using the Cummins thermostat.

https://www.genosgarage.com/product/ram-cummins-oem-thermostat-5292738/thermostat

 

[Timd32]

Yeah second the Cummins stat then, they are a bit different, I'm running a Gates I think. Hard to remember, it's not every minute for sure.

You could always test them in some hot water possibly to see them in action. Bit overkill for sure but if it's different with the new stat then the rule of the last thing touched could apply for sure.