Engine Air Compressor Noise

[sailor_lou]

Morning all,

I have a 350HP CAT C-7 engine and recently noticed that when the compressor is running under load, it makes a fair amount of noise. I say “recently noticed” because this is my first diesel and between all the other noises a diesel makes I am not sure if this is new or a sign of a pending issue. It is a mechanical knocking sound, similar to an extremely loud mechanical lifter, that I can hear over all the other engine noises. It stops as soon as I hear the unloaded valve open (air release), but starts again when the compressor is recharging the air tanks. Because of this I am assuming it is the compressor and it is only loud when it is under load. The tanks are being charged as normal (both charge time and pressure), but the noise does appear to be unusually loud to me. Are these things typically noisy?

I realize it’s tough to say it is a problem without actually hearing it yourself, but would be interested in the group’s thoughts and experiences. Also any other ideas, like a problem with a pinched air line or air dryer would be appreciated. I don’t want to just start replacing parts (ie: compressor) until I have a better handle on the cause.

Thx,

Lou
05 Travel Supreme 38DS04
Spartan Mountain Master, CAT C-7

[deltastar459]

I had the same concern as a new diesel owner. Cat advised me this compressor noise is normal.... deltastar459

[sailor_lou]

Thanks for the feedback. I had a CAT authorized repair shop check it out and the mechanic that looked at it told me it was noisey than expected and said they would replace it. At first they thought it was beyond warranty (05 motorhome), but since it was originally purchased in 06 they agreed it was stilll covered. The service manager told me the part was on order and I could pick it up in a few days. When I went to pick it up, the service manager told me they listened to it again and felt it was OK and they didn't replace the compressor. I pushed back, but he said there is nothing wrong and that they wouldn't replace it. I find it interesting that when they believed it was on my dime they were eager to change it out.

I still believe there is a problem there, but that they were concerned CAT wouldn't cover it since it hadn't failed (yet). I may just change it myself if it doesn't actually fail before the warranty period expires. In the meantime, I keep listening to every other motorhome I come across to get a feel for how loud they are.

Thx again,

Lou

[deltastar459]

Hey Lou, I have owned my Cat C9 for 3 years next mont. The first year I purchased it I took it to Cat complaining about the excessive noise and they checked it out and asked if I had ever owned a Cat before, when I stated no the advised that this was completely normal. That as I say was 3 years ago ans I still have a very loud compressor but nor problems with it's operation. It is only noisy when engaged. I am now out of warranty, be interesting to take it to a different Cat dealer and see what they say. But again it is working fine...... Deltastar459

[sailor_lou]

I am considering that, but the first one charged me $180 (investigation charge) to tell me nothing is wrong. I'm not sure what a new compressor cost but each time I get another opinion it adds up. I'm still thinking of just replacing it.

Lou

[94-Newmar]

My 8.3 Cummins w/compressor is sorta loud as well. I can hear it over other noises once I started listening for stuff.

[sailor_lou]

Thanks, you guys are making me feel better about the noise. Maybe I'm just being paranoid.

Lou

[wagonmaster2]

Quote:

Originally Posted by sailor_lou I am considering that, but the first one charged me $180 (investigation charge) to tell me nothing is wrong. I'm not sure what a new compressor cost but each time I get another opinion it adds up. I'm still thinking of just replacing it. Lou

I also have a Cat C-7 engine and find it's hard to believe that even under warranty a customer gets charged if they think something is wrong with the engine when there isn't. But I certainly do believe these shops will stick it to the customer any time they find an opening. I was charged $450 for a 2 hr 15 min valve adjustment at a Cat shop then they added another $53 labor for changing the fuel filter during that same time period. You'd think $200/hour should cover everything done without adding another $53. I think I'm going to start looking for a different Cat shop but they are probably all the same.

I'll have to start listening for my air compressor's noise. As you stated these diesels make so much noise how can you tell if anything is wrong. When I bought my coach new I asked a Cat/Freightliner shop when to have the valves adjusted and they said not until I could hear the tappet noise. I had to laugh, they aren't like the old Chevrolet 6-cyls that you could hear every tappet, piston slap, wrist pin, or connecting rod that got a little loose.

Good luck on your quest. Keep us informed on your choice.

Wagonmaster2

[sailor_lou]

I can understand a charge for their time, even if there is nothing wrong. However, what really bothers me is the first mecahnic spent 15 minutes (with me helping him) and determine the noise was unusually loud and recommended a replacement. Then once the service manager realized it was still under warranty, he made the decision that it's not a problem, charged me an hour and half worth of labor and said I was good to go.

I always do my own maintenance and the only reason it was in the shop in the first place was because it is still under the manufacturer's warranty. I just don't trust the "professionals," so once again, I'll take care of it on my own.

Thanks for the feedback. BTW, I'd would like to meet the individual that can hear a tappet noise on a diesel.....LOL

Lou