Scratching head help detroit 60S 12.7

When did this start, and what exactly are you trying to fix? It really sounds like your truck is operating like it should

 

let's talk about you rebuild, did they flush the block and head?

Replace the liners?

Waterpump?

Very unlikely.

My guess the system needs a good flush and to make sure that there isn't any blockage in the block.

 

If you're pulling a hill loaded, temp comes up, fan comes on. Does the temp go down?

What truck is this in? Sounds like your coolant temp gauge is driven by the ECM. So it is possuble the sensor is reading an incorrect temp.

As @Oxbow mentioned, the random fan engagement at different temps is probably your A/C high pressure switch turning the fan on

 

I thought 210 was normal from what I remember when I drove S60. I remember driving in Arizona in the summer heat and it was like 200 205 on temperature gauge when it was like 110 outside.

when I first drove the DD15 engine I thought something was wrong because this new engine run up to red line on temperature gauge before engine fan comes on.

I remember back when Kevin Rutherford has radio show some guys tried running S60 engine at hotter temperature to get better fuel mileage and the were running this waterless Coolant that would not boil. I don’t remember the exact number but they were running them at like 220 or 225 or 230 and they found out guys were cracking the head on the S60. I just remember I was suppressed how the S60 head could not take to much more then what they had it running from factory. I thought it was 210F was normal fan on temperature.

 

I am having a similar issue. My fan used to kick on at lower temps but now it’s higher like yours. I don’t have AC when I am sitting still because no fan and no airflow. I was baffled. Everything in my entire system was replaced in August 2022 with my engine rebuild EXCEPT my fan clutch solenoid.

I went ahead and replaced it last week. I hadn’t noticed on the old one, but there was a plug missing that left an open hole. I put a metal plug in and the fan ran nonstop. I did some more thinking and looked at some old pics. The plug that was missing is actually an exhaust vent. There is a small hole inside the threaded hole where air comes through. This also explains an air leak in my ac control in cab. If I would move to defrost it would stop.

I ordered the exhaust vent. It’s a $3 plastic part. It’s a few days out on shipping. The new fan solenoid from Freightliner doesn’t come with one. As irrelevant as that small plastic part seems, I think it is very important to the entire system working properly.

See the pics below. The first one is the home where the vent goes. The plug is what I used to troubleshoot. The second shows the exhaust vent. Freightliner part number Gtd 5060 1