On my 04.5 I've been having some coolant and trans temp issues. Coolant temps go up to about 200-210 and trans temps get to about 160-175. I've replaced the water pump,180 degree thermostat, a new fan clutch and the trans temp is reading from the pan. I know the trans temps aren't bad but it normally doesn't get above 150-155 on a 90+ degree day. Coolant on the other hand never got above 180 unless i was working the truck hard. After a 15-20 min drive is when things start to heat up, stays there for a few minutes and then creeps slowly back to normal. And this is with highway, city and or just idling in neutral. Doesn't matter. I don't have any coolant or trans fluid mixing and I'm not having any changes in levels from the trans or coolant. Could I have a blockage in my heat exchanger on the side of the block? Don't want to go through another transmission build or engine for that matter right now. Advice?

Welcome to the m1973m forum.

 

In comparison to the temps I run on my 05 the only thing I see wrong in your post above is the t-stat being too cold,  the trans is a bit warm if measuring in the pan but not bad if seeing that in stop and go around town driving.

What does your radiator look like externally and internally and how many miles are on it? Could be calcified on the inside.

The heat exchanger is just that it is not a cooler, it is to help things warm up better. The oil leaves the heat exchanger to go to the cooler.

Agreed 180*F is too cold. Should be 190*F thermostat. Also like Bill said how about the face of the radiator? I just had a Ford truck here that had really poor A/C cooling. After taking the time and blowing all the bugs out with a 3,000 PSI power washer the A/C is super cold now. You might have the same issue just packed with dirt and bugs. Might have to pull the radiator to get a good cleaning.

I fought a cooling issue for too long.  The radiator looked clean when it was installed.  it wasn't until I actually pulled it out that I realized out plugged it was.  It was a simple and cheap fix.

I agree with W&F that your only real issue is the wrong thermostat. 

 

What are you using to read coolant temp? The dash is mostly accurate.... but not completely.

 

The 190° thermostat that your truck should have opens at 190°±3°, but isn't full open until 207° and has a max allowable temp of 225°. Around 210° the ECM starts modulating the fan and it generally won't go to 100% below 215°. 

 

If your old thermostat never got above 180° than that was a problem and shouldn't be considered normal. 

 

Is your current thermostat a Cummins one? Lots of issues with the non-Cummins thermostats. 

 

A 180° thermostat has a couple of issues, the big one is if you tow. The max allowable temp on a 180° thermostat is 212° and as you can see above that's barely into fan operation as the fan is ECM controlled. The second is a cooler diesel is less efficient, so a reduction in economy or power is possible thou probably minimal with a 10° difference. 

The only non-Cummins thermostat that I would even try is a NAPA which I've had really good luck with.

I did install a Napa thermostat which I've never had issues with before either. I understand what everybody's saying about running too cool but where I'm located in south Tx temps reach 95+ in summer and I've ran a 180 thermostat for years and have never had an issue. Winter time I do run a 190 though. I just have never had both temps (coolant and trans) both go up like they have been. If I did have trans fluid in the coolant by some chance could it cause a thermostat issue. I also deleted the check ball valve recently just in case it wasn't letting trans fluid flow as it should. I should also mention that I have a Derale hyper cool remote trans cooler also. What about the thermostat that's in the factory trans cooler? I just wouldn't think that would cause coolant temps to rise though. 

And the radiator externally looks clean and whenever I wash the vehicle I always give them a good rinsing. I took a 15 min drive and checked the radiator and the cap was cool so I removed it and didn't see any coolant flowing through the fins like it should.  

I have read about plenty of NAPA thermostat issues on these trucks... Cummins is the only thermostat I would consider running.

 

The high spike could be a bad thermostat.

 

My 0.02 is to put the 190° back in year round even in 115° weather there are zero reasons to run the 180° but there are reasons not to.

 

Order or pickup a Cummins 190° thermostat and see where you are at.

 

You didn't say how you are reading coolant temps.

I'm reading temps from the gauge cluster. And the only reason I didn't run another Cummins thermostat was bcs it was the weekend and didn't have another option. 

I Agree w/AH64ID.. what he explained perfectly make complete sense. IF 180* THERMOSTAT just barely reaches the trigger temp for ECM to engage FAN into low/half speed "SOMETIMES" your gonna see a higher average temp with a 180* tstat than with a 190* with the 190 degree the fan will run more often especially at 100%. and it will reach trigger temp real quick and temp will fall bac to190-200 probably without notice

Like even my old school rig won't trigger full lock of the fan till at least 210*F. I do know that its partially locked at temps above 190*F. So I would still suggest changing theromstat first and trying again and see what happens.

MINE TRIGGERED AND ENGAGED WHEN ENGINE STARTS, 24/7       I HATE THAT P.O.S

I think when i finally get around to getting it off and replaced, I'm gonna swing by the Body Shop that installed it and leave it hang'n ON THE FRONT DOOR     

I've seen several of them seize the fan clutch be locked 24/7 like that.

My 05 will lock on start up and kick off when rpm get above 1300. Then I never hear it again.

I never hear my 05 but lots of people claim their 03-04's and 06-07's are LOUD...never hear that about the 05's thou??

are those trans temp correct? 150-155? mine runs 190 according to my edge almost even with the engine temp. do i have a problem?

I've seen several of them seize the fan clutch be locked 24/7 like that.

NO ,,,I'm sorry,, just assumed you had seen the post i had few months ago bout the fan,,,i had a dodge nitro run red-light and got my from-end "Radiator ,air charger, bumper and  riverside headlight completely totaled that nitro,,broke back sups almost off.. THE NO ACCOUNT BODY SHOP BOUGHT A CHINA MADE FAN CLUTCH ASSEMBLY FROM KEYSTONE..AND PASSED IT OF AS OEM

NOW it sounds like you have a window seat on AIRPLANE 

I never hear my 05 but lots of people claim their 03-04's and 06-07's are LOUD...never hear that about the 05's thou??

It's not every time. Also my truck sets a lot, it might be 4-5 days go by and some times more. I thought maybe the fluid settles in it or something along those lines. I live on a county rd and it's about 4 hundred yards to the hwy. I drive slow and you can hear it pulling air, I don't think it's fully engaged because I have heard them really making a loud noise. This wont last long, maybe 20-30 yards and it kicks out. It checks out ok the best I can tell, it has a drag when you try to turn it and no slack.