i have a isx engine and it will not get hot it sits at 120 temp i have replaced clutc

It says you have 17 years experience so I would assume you're talking while running but I have to ask is that your temp driving or at idle? In cold weather mine will drop to 120 at idle. Check your thermostat, may be sticking open.

 

I assume this is at idle. What rpm are you idling at? In the winter you want it idling at least 800 rpm, 1000 rpm is better, some I know idle at 1200 rpm when it's really cold.

 

Check Thermostat, my old isx was notorious for sticking open.

 

On big truck diesel engines, when thermostats fail, they fail open. My Series 60 did that same thing, it had 2 thermostats...not sure about the ISX, but the Detroit was a fairly simple and fairly cheap fix...afterwards, at idle (above 0 degrees) it would stay over 170.

until you get it checked, if you aren't getting much heat, turn on the cruise and hit the set button...it'll tach up a little higher and maybe put out some heat.

 

Sitting here in Somerset, PA. Its 9 degrees out and my ISX is idling at 700rpm and temp is holding at 180F. I would get the thermo checked.

 

I vote thermostats, or low coolant.

 

I agree, most likely the Thermostat or Thermostats are stuck open. If they are the original ones than they are due to be replaced. It's fairly easy to do yourself, except the Brass Seals are a pain to press in.

 

Mine did that. . Right before it spun a main bearing. .I'm positive one had nothing to do with the other, but $30,000 later. ..

 

Check fuse for fan may be blown keeping fan on. not sure what kind of truck but i have taken the fuse to keep from over heating