After draining, flushing and replacing water pump and t-stat I'm having some really weird temp issues. While sitting at a stoplight it reads 180, when I start driving it climbs to around 190 and then cools off again at the next light is it possible there is air trapped somewhere in the system. I followed the instructions in the article by moparman filling the block before installing the t-stat then filling the system via the radiator filler neck. How can I get it to burp the air out if that's the case. 

Ok @Mopar1973Man, explain this to me because I may have been wrong in my previous post.

 Are the fans on these trucks not like on a gasser where as the clutch engages to spin the fan at low rpm and releases it at higher rpm when there should be air flowing as road speed increases?

 I know on the "big rigs" they are controlled by a temp sensor and an air activated clutch but these are not, I have not noticed any electrical going to the hub either (but then wasn't looking for it).

 Not questioning your comments, just wanting to learn, I may have misspoke earlier. Thanks.

To me degrees is pretty much just a personal preference...you're not gonna harm your truck with either.  I've also heard that 190° is stock on our trucks...which is pretty much the temps I got before I changed.  Also heard that the hotter they run the more efficiently they run...so I slapped in a 200°.  I haven't noticed any difference in mpgs but the heater sure does work more efficiently.  And since all the 6.7's run 200° I figured if it's good enough for them...

Ok, so what would be the reason it would have a 180 in it. But the 190 one is the one I'm having issues with its like it's constantly opening and closing. My truck runs ice cold in the winter. I never idle warm it or It would take forever in winter I have a 15 mi commute in witch it doesent hit 180 till mile 15 in winter even after using the block heater when it's below 40 degrees in the morning. It's always been steady when it hits 180 never straying much more that a few degrees wether it's 30 or 105 why such weird swings now it will jump to 190 degrees after driving a block then dropping to 183 degrees two blocks later. Im confused 

The reason that the larger tstat causes wild temp swings is that my 190 degree will not open at anything below about 198 and then temp is so high that it opens all the way dumping a large slug of cold coolant through the motor and cant close fast enough to keep it at temp. This happened with both tstats installed 3 years apart. The way it acted makes me think that when running down the road the flow pressure might be so great that it does not allow the large tstat to open when it should and when it generates enough force it slams fully open because temp has gone to high. When I was a owner/operator I was taught back in the 80 that it was not good to heat cycle a engine and dumping a slug of ambient  coolant that fast has to cause a fair amount of stress and will shorten your engine life.

  On 6/25/2020 at 12:13 AM, Doubletrouble said:

Are the fans on these trucks not like on a gasser where as the clutch engages to spin the fan at low rpm and releases it at higher rpm when there should be air flowing as road speed increases?

 

The fans remain unlocked till the the thermostatic coil on the front of the fan sees enough temperature to twist the clutch lock. Now the fluid channels out to the disc and drags the fan till the thermostatic coil cools and the the oil is bought back to the hub of the clutch and now freewheels. Road speed has zero to do with it. You can be crawling the steep forest grades out here in 100+ weather and have it lock up the fan at 15 MPH. Again based on the amount of heat given off the radiator. Typically my truck lock the fan at  about 220*F then it pulls the cooling air till 193*F and unlocks. 

 

 

Edited June 25, 20204 yr by Mopar1973Man

So at this point im really considering putting the 180 back in due to the fact i need to haul my travel trailer this weekend to take my grandkids fishing and dont want to have issues with it until i can find the right t-stat all the ones i found have the flat bottom. Any ideas.

Is it possible I'm just Overthinking this situation and i. Just not used to watching a digital temp guage vs an anolog and that the swings are just the t-stat opening and closing. Its just that its happening over such short distances. 

  On 6/24/2020 at 10:47 PM, Bullet said:

All my gas motors idle hotter than my diesel does...they will keep the thermostat open at idle while my diesel will keep it shut.

 

The primary reason a gas engine heats to operating temperature rather quickly while idling and a comparable displacement diesel engine has a tough time getting to operating temperature while idling is because of the different way the air flows through each engine.

 

Gas engines have a throttle plate.  Diesel engines of our era and older do not.  A gas engine works like this:  an air and fuel mixture at the proper ratio enters the cylinder at a very low pressure at idle.  The engine actually has to work to draw the air-fuel mixture around a mostly closed throttle plate before the mixture enters the cylinder.  This creates a very low pressure downstream of the throttle plate -  a vacuum of about 18" HG.  That air-fuel ratio is at such a low density that it does not carry much combustion heat out the exhaust.  Most of the heat goes to the water jacket, so the coolant warms quickly. 

 

A diesel engine  with no throttle plate allows a full charge of air to enter the cylinder at idle and then a small amount of fuel is injected.  The air density entering the cylinder is slightly lower than the ambient air density so lots of heat from combustion can be carried out the exhaust and a lot less heat will go to the water jacket.  Plus, the engine does not have to work as hard to get the air into the cylinder in the first place because there is no throttle plate.  A fully engaged viscous fan doesn't help matters either - just what you need on a cold winter day - a fan blowing cold air over an engine that is struggling to warm up!

 

- John

  On 6/25/2020 at 12:17 AM, Bullet said:

  I've also heard that 190° is stock on our trucks... 

And since all the 6.7's run 200° I figured if it's good enough for them...

 

The OP has a '98.5, so oem was 180* so is a '99, the 190* started in '2000.

 

The 6.7 only used the 200* for model years '10-'12, all others use 190*

 

In my opinion, the higher temp stats were emissions drivin, not what was/is best for the Cummins. My '91 has 330k miles on it and is 29 years old, yet it has never had a head gasket, tappet cover gasket or vacuum pump seals, I finally just changed the water pump. It has 180* from day one. Same with my '90 Ford Cummins, all gaskets and seals are original.

 

My '01 oem was 190*, it has had all the gaskets changed and two sets of seals in the vacuum pump, 340k miles and 19 years old. I now run a 180* stat and all temps that matter are all cooler. Fuel temps and tranny temps to name two, reflect the 180* stat. I do haul heavy in high ambient temps all the time.

 

I am considering a fan clutch from a 180* oem truck. I think with my 180* stat it would match better than my 190* clutch. It locks at about 200* - 205* now. My '91 locks at 190-195.

Thanks @Mopar1973Man, learned something new today.

 I was under the impression that they worked on centrifugal forces alone. 

Do you get plenty of heat from the 180° in the winter?

  On 6/25/2020 at 2:34 AM, Dave f said:

So at this point im really considering putting the 180 back in due to the fact i need to haul my travel trailer this weekend to take my grandkids fishing and dont want to have issues with it until i can find the right t-stat all the ones i found have the flat bottom. Any ideas.

Is it possible I'm just Overthinking this situation and i. Just not used to watching a digital temp guage vs an anolog and that the swings are just the t-stat opening and closing. Its just that its happening over such short distances. 

 

If you can't find one local I would just order one from Cummins, Gates from Geno's or a Stant from O'Rilleys or Rock Auto. In the mean time I would change back to your old one.

 

https://www.oreillyauto.com/detail/b/stant-5674/cooling---heating-16773/thermostats-25043/thermostats-12876/555a1167c2f6/stant-thermostat/14288/5699633/1999/dodge/ram-2500?q=thermostat&pos=3

 

https://www.rockauto.com/en/catalog/dodge,1999,ram+2500+pickup,5.9l+l6+diesel+turbocharged,1377569,cooling+system,thermostat,2200

 

 

So is the bottom bump critical then

So Thursday I had olrileys order a stant for me when I went to pick it up yesterday they ordered a motorad that wouldn't work so I installed the old one and ordered a gates from Genos and having it delivered to where I'm going the guys at my local orileys seem to be complete boobs said they can get one but had to be special ordered.