2012 Isx15 acting stupid please help

[Mobilehomeguy]

New guy here….. here’s the rundown, I bought the truck with it running hot under a load. It is a 2012 peterbilt 386 demandated. A guy out of Bainbridge, Ga did the ecm work. The previous owners threw gobs of money at it with no luck, the previous owners had an inframe done, oem cylinder head, water pump, thermostat, oil cooler, had the egr cooler bypassed, new radiator, new CAC, new transmission. I bought the truck at a steal or so I thought. I went over the truck and found the IMAP sensor was broken where it plugs in and the fan clutch was slipping. I went ahead and replaced the fan clutch, imap sensor, baro sensor, and exhaust back pressure sensor. Drained all the coolant, new seal and thermostat, and flushed the system and topped back off. Truck has a 180* t-stat, bob tailing the truck runs between 185-195, I pull mobile homes so not real heavy but quite a bit of wind drag. With a 30k pound office unit running the south east truck will run a constant 200-210 on flat ground with the fan running 90% of the time at 10-15 pounds of boost at 68mph….. start up a hill and get over 20 psi thing heats up like crazy, it will get up to 225-230 pretty quick if you don’t baby it. I can keep the rpm’s low around 12-1300 and the engine will maintain temp around 205-215. Supposedly the truck is set to 575 which I feel is too much but I’m no expert. No coolant in oil, no cross contamination anywhere, no excess pressure or puking, no coolant loss…. Truck doesn’t want to build over 28-30psi….. best I can remember I should be seeing 36-38psi manifold pressure. I’m at a loss, is this all computer? Exhaust is cleaned and lightweight, truck seems like it’s using entirely too much fuel, what do I need to do?

[Rawze]

A lot to unpack there...

== The thermostat is supposed to be 185-F from cummins. Quite often when someone replaces the thermostat.. they do not replace that brass ring (or they do not install the new one properly, damaging it) in the bottom of the thermostat housing and this causes them to run hot all the time or overheat.

== Assume the program is garbage until you have it reviewed. More than 90% of all delete programs are. It needs to be copied out of the ecm and e-mailed to me for a proper review of what someone did in there.

== The EGR cooler COOLANT CIRCUIT CANNOT BE BLOCKED OFF!!!.. It is really hard on the water pump + it will make cylinder 5 and 6 run hotter than normal, eventually causing engine damage. - So if some idiot removed the EGR cooler, I hope like h#ell they put a coolant hose (3/4") from the water pump to the place on the block where the eGR cooler used to be.

== DON'T trust the inframe. VERY FEW repair shops any more will rebuild an isx worth a stick any more. Matter of fact, if someone told me it was freshly inframed.. I would have walked away from it in a hurry.

Sounds like you bought into a can of worms to me so far.

[Bengy88]

Hey man I’m gonna send you a pm. Your boost is definitely low especially if that’s 30 in a pull. I’m curious to know what your oil temperature is hitting and pyro if you have one…. If not you definitely need to invest in one. As Rawze states on a daily basis never assume that your programming is good…. They almost never are and this should be checked.

When you say egr cooler is bypassed I’m hoping that the correct piping is installed so that the #5 and 6 cylinders are getting proper coolant supply.

[Mobilehomeguy]

There is a pipe that was put in place of the egr cooler. Pyro is ordered, oil temp stays within about 10-15* of coolant at all times. I replaced the thermostat myself and installed a new brass ring/seal.

[Mobilehomeguy]

Cummins in forest park did the inframe and the head according to the company I purchased the truck from.

[Rawze]

(08-24-2023 )Mobilehomeguy Wrote:  Cummins in forest park did the inframe and the head according to the company I purchased the truck from.

then I would put little to no faith in the inframe ... unfortunately.

[JimT]

(08-24-2023 )Rawze Wrote:  A lot to unpack there...

== The thermostat is supposed to be 185-F from cummins. Quite often when someone replaces the thermostat.. they do not replace that brass ring (or they do not install the new one properly, damaging it) in the bottom of the thermostat housing and this causes them to run hot all the time or overheat.

Just wanted to chime in, when I did my inframe in 2020 I installed the new thermostat from the kit. Prior to inframe coolant temps would bottom out about 185. After inframe with the new thermostat my coolant temp has been 178 on the low end (and very steady there too). Not sure why the difference but I'd guess something slight changed with their thermostats.