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Not to hijack the thread but is it common for ISX compressors to have a knock sound to them? I have heard 3 of them including mine that have a knock or rattle sound at idle when pressure is high. Mine will stop when air drier pops off then knock builds as pressure builds? Common or compressor problems ahead?
If someone replaced or re-installed the air compressor and did not time it properly then it can be louder than normal. Maybe this helps...



My cm870 knocked while running and would be silent while not. This was both on a 1.1 million mile engine and a fresh cummins cert. Reman. Both were definitely visually verified and done to exact cummins install spec. By me. I chalked it up to the nature of the beast on this one. I ran both engines for a total of 700,000 miles with no compressing problems.

My 600,000 mile cm871 is smooth and silent always. But I've heard plenty of guys say the same knocking in theirs is normal.
Thanks for all the input guys. I have a few more loads to cover before the end of the year and then I’ll replace it.
(12-19-2020 )Precisionw900 Wrote: [ -> ]Not to hijack the thread but is it common for ISX compressors to have a knock sound to them? I have heard 3 of them including mine that have a knock or rattle sound at idle when pressure is high. Mine will stop when air drier pops off then knock builds as pressure builds? Common or compressor problems ahead?

Check for air pressure between your compressor unloader port and governor when the compressor is pumping. Mine would rattlesnake when getting close to pressure cut out and quit once the compressor unloaded and the dryer purged. The governor was passing at higher pressures causing the air dryer purge valve to pop and sputter. Replaced the governor and good to go. I have also heard of this happening if cutout pressure is set to high to begin with. Simply adjusting the governor to a slightly lower cut out pressure solved the problem.

A Carboned up compressor head could cause a similar sound when unloader valves are sticking or not reacting as quick as they should. Cummins has a cleaning procedure on quickserve but a quick and dirty way is to pull the inlet tube and discharge line and let it suck a little wd40 or seafoam through the inlet while the compressor is loaded to lube and clean the internals.
Questiion,

Is it ok to add alcohol to air tanks on a demandated unit?
(12-20-2020 )amermextrucker Wrote: [ -> ]Questiion,

Is it ok to add alcohol to air tanks on a demandated unit?

To keep the tanks and airlines from freezing? If so, yes, I use STP gas treatment, the red bottle, that small bottle opening makes it easier to pour the liquid in the airlines.

https://www.walmart.com/ip/STP-Gas-Treat...e/16817400

$1.50 a bottle, and a bottle normally lasts all winter.
(12-20-2020 )amermextrucker Wrote: [ -> ]Questiion,

Is it ok to add alcohol to air tanks on a demandated unit?

Makes me wonder why someone would think they have to alter the compressed air system on a truck that was demandated vs. stock?

I cannot think of any.
(12-20-2020 )Waterloo Wrote: [ -> ]
(12-20-2020 )amermextrucker Wrote: [ -> ]Questiion,

Is it ok to add alcohol to air tanks on a demandated unit?

To keep the tanks and airlines from freezing? If so, yes, I use STP gas treatment, the red bottle, that small bottle opening makes it easier to pour the liquid in the airlines.

https://www.walmart.com/ip/STP-Gas-Treat...e/16817400

$1.50 a bottle, and a bottle normally lasts all winter.

Being stp gas treatment, is made with jet fuel. I'm thinking, it wouldn't be a good idea to have this product in the air system whereas the air pressure is as high as 120 lb. I know from prior experience pulling tankers hauling flammable or combustible product, you never unload utilizing pressurized air, since pressure creates heat.
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