isx cm871 coolant pressurized

[Waterloo]

EGR Cooler is blocked off eh? Well, there may be other issues then. Have you done the exhaust gas coolant test? You can get a kit at NAPA for around $20 or $30. I would start there, that will tell you immediately if you are getting exhaust in your coolant system and then go from there... Are the coolant lines to the EGR Cooler blocked off?

[gonzo1949]

No the coolant lines still flowing. I'm getting some pressure into my coolant and it give me a low coolant light. Not all the time it's intermittent

[Waterloo]

Good on the cooler lines. Are you having to add coolant on a regular basis or is the coolant staying in the system and just fluctuates the level? If you are losing coolant, and cannot find the source, tighten all of your clamps. If the system is pressurizing, it is either your compressor or head... But you know that. If you are plated off, I am thinking it may be your head... How are your EGTs?

[gonzo1949]

No its just fluctuating. Yea I figured. Have to check the compressor. Shouldn't I have other symptoms if it's the engine head and or gasket?

[Waterloo]

Mine started just like you are describing, no visual signs. I drove mine for months like that, and then it started taking out hoses, than the radiator, then my Tri Pac... When I fixed the latest blowout she was shooting coolant a foot in the air until the thermostat opened up... I drove her 16 miles to the shop for the in frame last week and the reservoir bottle was ready to explode... Definitely test the compressor, and I would still do an exhaust gas coolant test just to be sure.

How many miles on the truck? What year and model?

[gonzo1949]

Thanks for the info. I'm driving with the second coolant cap slightly loose so it won't build pressure. It has 580,000
2010 peterbilt 386

[Waterloo]

Is it losing coolant through the cap when it is tightened down? And have you bought a new radiator cap? These caps do go bad... Never mind, I see you are on your second cap.

[Waterloo]

Why is the EGR Cooler plated off? Someone do a tune on her?

[gonzo1949]

Yep it started loosing coolant thru the cap. On the way home Sunday I stopped at a rest area and found the top hose about to pop with a small hole in it. So I let the pressure out by releasing the cap. Took it to my local mechanic and he told me he thought it may be the compressor was ro busy to check it. That was yesterday