Cummins isx air pressure in cooling system

If it's not the head gasket then it's more than likely the air compressor. go to a shop that can check the amount of pressure in your reservoir and then disable the compressor. plug the inlet air pipe and open both air tanks to relieve air pressure and see if your cooking system pressure drops.

Don't trust speedco. get a mechanic to test the coolant system for compression or buy a kit from Napa for like 20 bucks.

if there is a vent/overflow tube on the reservoir, make sure it's clean.

the very cheapest option is that your reservoir cap is bad. they are pressure relief.

 

If your truck has been d3l3ted, then its either the compressor, head or head gasket. Depending on the mileage of the engine, if the gasket failed, its highly recommended to check liner protrusion, Cummins ISX are known for sunk liners causing head gasket issues. My hunch is your having head/head gasket issues, if the coolant reservoir is getting darker, normally its an indication of combustion gases in the cooling system, there's a test with liquid and vacuum pump that can be used to confirm combustion gases being present in the system, if the fluid changes color, then start pulling the head. Do you have the horsepower/torque cranked up too?

 

I have this same problem with mine and my air compressor secondary air drops while I'm driving. So what does the air compressor have to do with The cooling system.

 

coolant runs through the air compressor head, if the compressor head cracks, air pressure is much greater than cooling system pressure which is max. 15 psi, and so it would pressurize the cooling system, if your truck doesn't hold air overnight...I've also seen cases where coolant will seep into the compressed air system when truck air pressure gets low enough, and you'll have some coolant in your wet tank. All depends on the nature of the failure. EGR coolers, cylinder heads and head gaskets can fail and pressurize your cooling system with combustion gases. There is a tester available with a liquid that changes color at the detection of combustion gases, if the blue fluid turns yellow(that's what my tester does) then it has detected combustion, if not, then i would pursue the compressor

 

What was the outcome of your combustion test? What did you end up doing for a fix?

 

With a residue on coolant tank walls it could also be and oil cooler beginning to fail

 

The last truck I used compression gas tester on picked up nothing. Just to be safe I bypassed the air compressor and was still getting coolant pushing out. Removed the head and the liners had sunk. The engine before that when I did the test I got immediate color change on tester fluid. Pulled that head off and it was cracked and had blown gasket in two spots. The compression gas tester is a good tool but I have found it to be inaccurate at times.