This week I installed a new heater core and with that I flushed the radiator, installed a new thermostat and radiator cap.  I pulled the radiator while I had it empty to inspect it for blockages and it looks great.  Before I took it apart it was starting to run a little warmer then usual especially when under a heavy load, but it never overheated..  I had suspected that the thermostat was going bad.  I put 50 miles on it after flushing it and changing those parts and the temp held steady and nothing was out of the norm.  Until I drove home last night.  On the freeway the temp sat at around 160*.  That is after it warmed up to just above 190*, then it dropped down and sat there steady.  If I got on the accelerator it would rise to 190*.  Maybe I got a bad thermostat?  It is a 190* thermostat from Napa.  I'm not sure what else would cause this, would air in the system be the cause?  I've never had a car or truck run cool like this.  The outside temp was 50*, so nothing strange.  

 

The thermostat that I put in had a rubber ring that sat around the thermostat, the old one didn't have anything like that... 

Sounds like it's stuck open. 

 

By rubber ring do you mean a gasket? They should all have one. 

 

Lots of horror stories with non-Cummins thermostats. I'd replace it with one made by Cummins. 

7 hours ago, Hawkez said:

The thermostat that I put in had a rubber ring that sat around the thermostat, the old one didn't have anything like that... 

 

It might be worth the time to inspect the new thermostat without removing it.  If that rubber has separated, then coolant would be bypassing the thermostat at a low rate and it could match your symptoms.  If the seal looks good, then remove the thermostat and check if any debris is lodged in the operating part of the thermostat.  Sometimes it takes awhile for debris to settle after a radiator flush because you can't get all of the debris out.

 

- John

NAPA thermostat has been excellent replacements. I'm currently playing with a 180*F thermostat. The newest version from NAPA has a much wider mouth than past versions. Never had a NAPA thermostat fail yet. Alway gotten the miles out of them and never left me too cold or overheating. 

 

Edited November 9, 20186 yr by Mopar1973Man

1 hour ago, AH64ID said:

Sounds like it's stuck open. 

 

By rubber ring do you mean a gasket? They should all have one. 

 

5 minutes ago, Tractorman said:

 

It might be worth the time to inspect the new thermostat without removing it.  If that rubber has separated, then coolant would be bypassing the thermostat at a low rate and it could match your symptoms.  If the seal looks good, then remove the thermostat and check if any debris is lodged in the operating part of the thermostat.  Sometimes it takes awhile for debris to settle after a radiator flush because you can't get all of the debris out.

 

- John

Both of these are my answer too...but easier to copy someone else's work.

How did the heater core go? I’m putting my interior back together this morning. I didn’t mess with the evaporator like I should have but oh well. It’s honestly only as much a pain as you make it. 

11 hours ago, Tractorman said:

 

It might be worth the time to inspect the new thermostat without removing it.  If that rubber has separated, then coolant would be bypassing the thermostat at a low rate and it could match your symptoms.  If the seal looks good, then remove the thermostat and check if any debris is lodged in the operating part of the thermostat.  Sometimes it takes awhile for debris to settle after a radiator flush because you can't get all of the debris out.

 

- John

I pulled it and looked at it last night.  The rubber has not separate and I didn't notice any debris.  I reseated it today and I'll take it for a spin around to see if the problem continues.  If so, I replace this T-Stat.

57 minutes ago, Marcus2000monster said:

How did the heater core go? I’m putting my interior back together this morning. I didn’t mess with the evaporator like I should have but oh well. It’s honestly only as much a pain as you make it. 

Replacing the heater core went really well.  The new core didn't come with the weather stripping that the old one had, so I put some on it.  Did you pull your HVAC box?

Pop it into a pot of simmering water & see at what temp it opens & closes.

 

Use a laser temp gun aimed at the wax pellet or a drop in thermometer with the tip not touching the pan.